This news flash about a seemingly obscure topic is of immediate importance to all our architect Title 24 clients -and it’s good news for a change. The Quality of Insulation Installation credit is a HERS test that can help design projects to achieve Title 24 energy compliance, and we’ve had a couple of nasty surprises with it in the past.

Apparently, up until around yesterday, the California Energy Commission did not officially recognize the QII test as valid for open-cell spray foam. Our insulation expert James Morshead of SDI Insulation actually sent me an urgent email yesterday with the news, saying:

Today the California Energy Commission stepped out of the 1980′s and into the 1990′s! The 1/2 pound density spray foam QII check list has finally been approved after long delays.

There will be further revisions and refinements but our State has finally caught up in its own way. They have finally acknowledged what the rest of the country has known and what we have known in our area for years; spray foam works whether its closed cell 2 pound density or open cell 1/2 pound density.

Now on to fixing the U-Value tables!

Active lobbying at the CEC is necessary

As usual, James was an endless trove of insider information. Apart from the news itself, the way that this came about was very revealing of the CEC’s  inner working processes. Most of us don’t understand how or why regulations are the way they are, or how agencies like the CEC solicit input from the public. Apparently one must be prepared to show up in Sacramento at multiple hearings, cultivate deep relationships with CEC staff, sift through the raft of proposed changes for the few items that might be relevant to your industry or situation, and be prepared to pounce on proposed changes with a formally structured submittal process. In other words, hire a full-time lobbyist.

A QII teaching case with the New Solar Homes rebate

We’ve run into some issues on the QII test before, where we’d called it out for extra credit on a Title 24 report on a project that was going for the New Solar Homes rebate. The house had to beat Title 24 by 15% to qualify. James Morshead was actually the insulation installer on that job, and clearly remembered how the HERS rater – NOT one of our Green Compliance Plus Affiliates – flatly refused to accept the low-density spray foam. Closed-cell was fine, but open-cell? No way. This was maybe the first time we’d ever used the QII credit, and nobody, including our other HERS raters, could tell us much about this obscure little omission that suddenly threatened the validity of the project’s energy compliance documentation – and the NSHP rebate. There was much tearing of hair and gnashing of teeth all around.

This close-up shows examples of open cell and closed cell spray foam, also known as low-density and high-density foam. Each cell in the high-density foam is closed, making it a better air barrier - which increases its insulating value.

Whys’ this QII change so darned important?

What are the ramifications of this change and how did it come about? “The recognition of open-cell spray foam has been in process for six and a half years,” said James. “We at SDI didn’t know how the CEC process worked. We thought the CEC would be actively looking at the market to incorporate new developments in a proactive way. But they’re not set up to do that. They’re set up to be reactive, influenced by lobbying input from stakeholders in the marketplace.”

He mentioned a long-ago fight between manufacturers of cellulose and fiberglass insulation, each of whom pushed to have their own products recognized as higher efficiency (higher R value) than the other. “That’s normal business. The CEC is a government agency, and that means that they’re encumbered themselves by a lot of regulatory process. They’re restricted by the system themselves. They rely on input from competing parties, and they solicit information by saying, ‘We want your input.’ They rely on the stakeholders to approach them and provide the necessary technical information.”

But presenting this input to the CEC can be an uphill battle. James mentioned meetings that would be cancelled without notice, web site meeting schedules that were not updated to reflect changes or cancellations, and a very skeptical audience. “They’re coming from an analytical and academic standpoint, but they’re NOT in the field.” And that’s the main point of this discussion, is that until the CEC actually went out to see a low-density spray foam installation, they didn’t believe it worked AT ALL. “They were writing regulations without ever having seen it in action.”

James went on to emphasize that he didn’t fault anyone at the CEC, in fact he admired their work and didn’t envy their task. They’re overworked, underfunded, well-intended, and very committed to the overall goals of helping California to achieve greater energy efficiency. They are doing their absolute best within cumbersome bureaucratic processes that they can’t change, either. To get an an idea of how slow the cycles are for code revisions, consider that the current version of the California energy code, the 2008 code, actually didn’t go into effect until 2010. And, some of its provisions weren’t enforced across the board until October of 2011.

Meritage Homes – a study in foam

Then we got on the topic of Meritage Homes, a high-end home developer who was apparently instrumental in adopting and demonstrating the real value of spray foam. Meritage’s Green FAQ page actually talks about the building envelope as separate from the appliances. James told me that Meritage had decided to use 100% spray foam in all its new developments. Their homes weren’t selling, because of the economy of course – not because the homes were bad. Nobody was buying anything, no one could get financing.

“But then, someone convinced them to foam their homes. The first batch was in Houston, TX. And the spray foam was so effective as an insulator that it ended up causing them some problems early on. Suddenly, all the A/C units in the foam-insulated homes were grossly oversized! Short cycling and such. And they had mold problems as well. But they also realized: OMG! this foam works way beyond the calcs!”

Meritage Homes is a high-end home development company that has implemented energy efficient building envelopes as part of the core design.

And that’s where we get back to the CEC, and the California energy code, which has all sorts of tables and appendices with the allowable thermal values that you can use for various types of wall assemblies and insulations: wood frame, metal frame, etc. (They even have an appendix table for straw bales now.) So, even if your insulation is NASA-quality, the CEC’s Joint Appendices might disallow the use of its true performance capabilities when doing home energy calculations. Which isn’t really fair, considering how difficult it’s been to get even ordinary home designs to meet current California energy standards.

The deconstructed home as sales tool

Most of the time, developers will have a few finished-off model homes that prospective buyers can walk through to see what their home will eventually look like once it’s built. But Meritage did something different. They had a model home with cutout walls to show the interior building assemblies, including studs, wiring – and spray foam insulation. “I call it the deconstructed home,” said James.  “People now are smarter, more educated about building and energy efficiency. They want to see what’s inside. And sales took off! It was a totally new way to sell houses. Local building inspectors liked it, too.”

The homes weren’t selling for more money, but they were selling a lot faster – and, to investors, time is money. The quicker you can recover an investment, the less financing costs you have.

By showing a "deconstructed home" rather than the usual finished showcase model, Meritage Homes has educated homebuyers on construction techniques and efficient building envelopes. This image shows a deconstructed Meritage home from one of its San Antonio developments, as shown on housingzone.com.

CEC’s focus on new construction ignores issues for remodels

Then our conversation touched on another issue with the current California energy code, and that is its almost obsessive focus on NEW construction. One goal at the CEC is for all new homes built after 2030 should be Net Zero. But remodels to existing homes also impact the energy grid, and at least in California, remodels right now represent a significant portion of current construction activity. (This is according to James – I haven’t yet found any data specifically comparing either dollars spent or number of projects of each type, in CA).

Sometimes this results in a very artificial situation when we try to show compliance for a remodeling project. It becomes an exercise in hoping that the project qualifies for prescriptive and we don’t have to run an energy model. For example, if a remodel is not adding any square footage, but the total glazing area is over 20% of the floor area, there are situations where the project just doesn’t qualify for prescriptive compliance. And let’s say that this is a low-budget project; they’re changing out the heating system and enlarging a couple of windows and leaving the rest alone, maybe it’s mainly an interior remodel which doesn’t affect the building envelope.

Well, there are times we’ve had to run a whole-building model that included all portions of the existing home that aren’t being upgraded, but which aren’t built to current energy standards. It’s easy to go down a path of adding new energy measures that not only add to the cost of the project, but which can just get ridiculous. Open more existing walls to re-insulate? You could trigger a seismic upgrade. Replace all the windows? Well, maybe the old windows were still perfectly good, why throw them away? Is that “sustainable building”? I’ve spent hours reading the Residential Compliance Manual’s sections on alterations and remodels, and sometimes writing to the CEC, to find out what’s really allowable.

Trying to get a small remodel to pass California Title 24 compliance can be more agonizing than modeling new construction. This vintage contortionist image is from "The Circus, 1870-1950" published by TASCHEN.

QII checklists for each type of insulation didn’t include one for open-cell spray foam

James reminded me that the HERS rater has to follow different QII checklists based on which type of insulation is used in the project. So there’s one QII checklist for fiberglass batt insulation, and a different checklist to use for blown-in, etc. Here’s a nice checklist writeup from ConSol, an energy group based in Stockton.

This checklist does not affect allowable R-values used in the Title 24 performance calculations. All it does is say that insulation should be installed evenly with no air gaps, empty spots, or compression, and that wall cavities should be sealed to limit air flow through permeable insulation types. The extra credit is really a make-up because the assumption is that typical insulation installation procedures are so shoddy that substandard installations are the norm rather than the exception. So, what’s not to like about open-cell spray foam exactly? And yet, because the CEC had no official checklist that was specific to open-cell, and they didn’t want to lump open-cell and closed-cell together, the omission has led many HERS raters to conclude that low-density spray foam was simply not allowed for the QII credit. That may in fact have been the official CEC policy, too.

Some HERS raters have very extensive backgrounds in building efficiency, construction, and green building; others just don’t have the same depth of knowledge. That’s one reason we chose to list some HERS raters on Green Compliance Plus who we felt had a better grasp of the underlying principles behind Title 24 energy compliance. Our HERS rater affiliates are people with multiple credentials: some are HERS and GreenPoint Raters, some also have CEPE certification, and most have other creds ranging from Energy Star to BPI to LEED for Homes. They already have experience working with integrated project teams on custom home projects, and are more proactive about anticipating potential situations ahead of time or recommending solutions instead of just showing up for the inspection and saying, “Well, you fail, and there’s nothing I can do to help. You won’t get your rebate after all. ‘Bye, now.”

The CEC doesn’t always realize these ramifications until they’re pointed out

On the above mentioned NSHP case study, when James brought this up to the CEC staff and engineers, they were appalled. They had never dreamed that their policies would ever lead to a situation like this. The HERS rater had said, rather erroneously, “This product doesn’t work. Therefore, it’s not allowed.” What he really should have said was, “This product doesn’t have an authorized CEC checklist. And it’s still not allowed.”

Checks and balances to prevent cheating are well intentioned, but they can really gum up the works

“The CEC really wants to discourage cheating,” said James. There are certainly more steps to verification now than in the 2005 code. The whole CalCERTS registry process, with online filing of  the tandem forms for the Title 24 energy compliance report, the installation certificates, and then the HERS certificates, is a great idea but a royal pain in the bum. The online workflow is especially agonizing for custom remodel projects. The CalCERTS support folks are very nice and they also have to follow a ton of regulations that attempt to cover every possible home construction scenario; they’ve never had to consider a different workflow for custom homes where an architect is directly involved.

The code update process is complex and unforgiving, not unlike San Francisco’s planning and approvals process.

So – what if someone wants to advocate for, say, a better attention to remodels, or to custom architect-designed homes? You’d better have a full-time staff person on the job. “The process is so cumbersome, with hearings, submittals, and a lot of 45-day language,” said James. (Really it’s just like the SF planning process) “It’s really arcane – miss something and you’re dead.”

Other industries have their own issues to push for in the energy code. “HVAC, energy consultants, builders… there are a few people who practically sleep in their cars down at the SMUD building in Sacramento.”

It helps to establish a good rapport with the CEC staff, who got high marks from James for dedication and responsiveness. “If you know the system really well, you can know which events are important, but you can’t tell just by looking at the CEC site. It’s a labyrinth, and you need a guide. Try to have a relationship with the CEC staff. They can help you get your voice heard.”

Is the Net Zero goal realistic and achievable by 2030?

James thinks that the goal of having all new homes built in California after 2030 be Net Zero Energy is unrealistic, and not the best way to reduce overall building energy use statewide. “NZE should be affordable to more people than it is right now. We should be making it easier for people to comply even as we tighten the standards. It would be better to reduce energy consumption by 40-50% rather than try for some exotic concept like Net Zero. Go for more basic stuff – air sealing, HVAC sizing, more credit for unventilated roof assemblies.”

“Net Zero Energy is a great idea,” he continued. “But in the construction industry, there are so many different kinds of people involved. There are builders large and small, plan checkers, building inspectors, HERS raters, architects, energy consultants… no one knows how to do it right yet when it comes to energy compliance. Right now, this education is being force-fed into the system when people aren’t ready. NZE is such a complex concept, it requires a very integrated approach. If you push it on people too fast, it’ll be a disaster in the implementation.”

I can’t argue with him there.

OK, I’m the first to admit that I know next to nothing about water heaters. Aren’t they those white cylinders that live in garages, as far as possible from the kitchen and the shower? Well… yes and no. In our Title 24 work, which is architect-designed custom single-family projects, the water heater is usually the last thing on anyone’s mind. However, on many of our analysis projects, the quickest, cheapest way to comply with California’s stringent energy-efficiency requirements has been to upgrade the water heater – and sometimes, to include a solar hot water credit.

This article explains how to assess water heater efficiency numbers, including the use of a handy lookup database at the California Energy Center’s web site.

California energy compliance calculation shows separate scoring for three main energy areas: heating, cooling, and water heating. A proposed design, here for a custom single-family home, can be behind on both heating and cooling and still make it up with a high-efficiency water heater.

Why’s water heating so important all of a sudden?

Well… if if a project is behind on heating AND cooling, and it’s already maxed out every other trade-off measure, it can sometimes be salvaged by running it with a more efficient water heater, specifically, a tankless. You’ll really feel the pinch if your project needs to exceed Title 24 by 15% or more. This is a basic requirement for almost all of the “beyond compliance” green standards: GreenPoint Rated, CALGreen optional tiers, LEED for Homes, and incentive programs such as the New Solar Homes Partnership. Local California jurisdictions are adopting various forms of these optional tiers, in some cases requiring very high GreenPoint Rated scores for larger homes.

“The equipment you see with values above about 90% are condensing equipment that have great efficiency values but need different installation practices and cost a bunch more,” warns Ken Nittler, creator of the Micropas Title 24 energy modeling software. “The most common equipment we see are small storage water heaters with energy factors of 0.60 or 0.62. On tankless, we see energy factors of 0.82 or so. On tankless condensing units, we see 0.94 energy factors.”

General Compliance Notes

Radiant Heating. Some basic questions that affect water heaters in Title 24 have to do with the heating system: specifically, whether radiant heat is under consideration. When you run a Title 24 calc with radiant heat as the specified heating type, the water heater drives both the Heating and the Water Heating portions of the score. The Heat score is sensitive to the water heater’s Recovery Efficiency, while Water Heating is associated with the water heater’s Energy Factor.

Solar Hot Water. There’s a very substantial credit for solar hot water in Title 24. You’ll need to know the “insolation fraction” which is the portion of total hot water that you expect to receive from solar thermal. A realistic number may be 25-50%, but that depends on how much sunshine the house will actually receive based on weather, site configuration, surrounding buildings and landforms, house footprint and available space for solar thermal panels, shade trees, and the like. Plan on having a supplemental unit such as an indirect storage tank or an additional water heater, since you’ll need hot water at night as well as during the day.

Radiant + Solar Hot Water Combined. If you’re going for radiant and/or solar hot water, you’ll need a mechanical consultant with strong knowledge of the differences among different manufacturers and unit types. For one thing, radiant heating water temperatures may be different from what you’d need for domestic hot water, so if you’re running them off the same unit or the same tank, specialized installation or components may be needed.

No Electric Water Heaters, Please! Fuel source, such as whether the water heater is gas-fired or electric, has a big impact on Title 24 compliance. Even for all-solar homes. There’s a huge penalty for electric resistance – that’s all you need to know for today’s discussion.

What’s the Highest Efficiency Realistically? The technology inside the water heater, such as whether it’s a two-stage condensing system or a hybrid, can have an indirect impact on Title 24 compliance. Sometimes if something’s not passing I’ll just test some of these numbers to see what happens, but eventually the numbers have to be realistic. This is where I asked around a bit to make sure that a water heater with a .95 efficiency was a real animal. It is – for a tankless. Condensing boilers also can have efficiencies as high as .95. There may also be condensing storage water heaters available, probably at a high premium.

Tankless or instant water heaters typically offer higher efficiencies, and thus are an advantage for demonstrating California energy compliance. Their real-world efficiency depends on other factors such as their proximity to the point of use.

Installation Issues. Do yourself a favor and check with your builder and subs before specifying some of the high-efficiency condensing water heaters. “The equipment you see with values above about 90% are condensing equipment that have great efficiency values but need different installation practices and cost a bunch more,” notes Ken Nittler.

Types of Water Heaters

Water Heater vs. Boiler. What’s the difference between a water heater and a boiler?

• Water heaters cost less and operate at a lower temperature. The “small” version, more typically used for small to medium sized residential dwellings, has an input under 75,000 Btu/hour. Large water heaters have an input that is over 75,000 Btu/hour.

• Boilers make scalding hot water, and more of it, typically around 200 degrees Fahrenheit. That’s why it’s called a “boiler”. A boiler is primarily intended for space heating (radiators), rather than making hot water for daily use. However, boilers are less adaptable to making hot water at lower temperatures at the 120 degrees for showers or 120-135 degrees for radiant flooring.

• They use different efficiency measures, and this last point is what’s crucial for Title 24 compliance.

Indirect Storage Tank. This is a separate, insulated storage tank with a heating element that can be used to collect and store hot water from an intermittent source such as solar thermal. It doesn’t actually heat the water up, it just keeps it hot after it’s already warmed by some other means.

Energy Compliance Calculations – Inputs Needed

Title 24 Defaults. About 90% of the time, we run our Title 24 projects using the software program’s built-in default, which is a small storage water heater with an energy factor of .60. This is a safely conservative assumption, since you can only go upwards from here. Within the Title 24 software, it’s the efficiency that seems to matter, rather than the number of units installed. In reality, however, larger homes are likely to have a boiler, or perhaps several different units at different locations.

Example of one of the pre-created sample inputs for the Micropas Title 24 compliance software. The values used here are specific to the water heater product specified, and they can influence whether or not a project meets compliance standards or not.

Efficiency Measures. Although the array of water heating technologies seem to be almost endless, the only thing that matters for energy compliance are these efficiency ratings, and they’re different depending on whether it’s a water heater or a boiler, whether it’s hooked up to a radiant heating system, and for water heaters the Btu input. There’s some confusion of terms here; I’m sticking to the terms as they are used in the Micropas software inputs.

Energy Factor. Used for “small” water heaters under 75,000 Btu/hour. The energy factor (EF) indicates a water heater’s overall energy efficiency based on the amount of hot water produced per unit of fuel consumed over a typical day. It’s a sort of umbrella measure that includes the recovery efficiency and standby loss measures described below, and is expressed as a decimal fraction between 0 and 1. An EF of .60 is average, while one of .80 will yield noticeable improvement in a project’s Title 24 compliance score.

Recovery Efficiency (sometimes called Thermal Efficiency, or AFUE, although they’re not exactly the same thing). Recovery efficiency is for “large” water heaters and boilers that are 75,000 Btu/hour or above. This is a measure of how effectively the unit turns fuel into heat. It is measured as a fraction between 0 and 1, higher being better. This seems to affect compliance score when radiant or hydronic heat is the main heating system.

Miles Hancock says, “Thermal efficiency is a useless number, measuring the unit’s efficiency at boiling water… what’s key is keeping that water hot, which is the standby loss. Standby loss is what kills the energy compliance.”

Standby Loss. Used only for “large” water heaters with a storage tank, this is the percentage of heat loss per hour from the stored water compared to the heat content of the water. In other words, once the water’s hot, how long does it STAY hot? This is measured as a fraction as well, in this case lower being better. The software built-in for the sample large water heater shows a standby loss of 0.03. Miles

Internal and External Insulation R-Value. Used for indirect storage tanks only. I haven’t tested the effect that this would have on residential compliance, because indirect storage tanks aren’t as common a configuration for the custom home projects that we analyze.

One thing that doesn't affect energy compliance is the style of the faucet - only what's behind it.

Other Inputs. There are additional inputs for heating element type (gas, electric, heat pump), rated input for gas heaters in Btu/hour, storage tank volume in gallons, distribution type, and for some types of water heaters, pilot light size in Btu/hour. For almost all our projects, the fuel type is always gas, since electric water heaters are discouraged.

The distribution type has to do with the piping configuration, and that’s mainly for larger residential projects. Example values are “standard” (the default), “Point of use”, or various recirculating on-demand varieties. I’ve occasionally run projects with these different distribution types to see what difference it made, and for a typical 4,000 SF single-family residential house, it made almost no difference in the compliance score. Sometimes it can make a big difference in the real world, though, so if you or your client are trying to maximize actual energy efficiency, as opposed to just complying with Title 24, try reading up on it in Ann Edminster’s book “Energy Free”.

Heater/Boiler Systems in the Title 24 Software Model. This is based on Micropas, which is one of two programs you can use for California energy compliance. I haven’t used Energy Pro as much, and it’s organized a bit differently. Here are a few basic types of heater/boiler systems that are set up as default or example entries in Micropas (and why you would pick one or the other):

• Small Storage. 40,000 Btu, 50 gallons, 0.60 EF. Use for legacy systems or if you don’t know what else to specify, and you want to assume the lowest allowable efficiency for the time being.
• Large Storage. 100,000 Btu, 100 gallons, 0.77 RE, Standby loss 0.03. Realistically this would be used for a larger home. However, I have noticed that specifying a large storage as opposed to small one lowers the compliance rating, probably because of the higher input rating.
• Tankless (instant). 195,000 Btu, EF .80, RE .76. This is the equivalent to a small storage water heater, and would be used in comparable applications such as a single family home as a more energy-efficient alternative. Compliance advantage is that it’ll boost the water heating portion of the score by as much as 30%, and it’s often a good choice in the real world as well. Real-world advantages: higher efficiency, theoretically endless hot water supply, smaller footprint. Real-world disadvantages: must be located close to point of delivery in order to realize energy savings.
• Boiler. 250,000 Btu, RE .80.
• Instantaneous boiler. 250,000 Btu, RE .80. Same as a boiler, but without a storage tank.
• Electric Storage. This is an electric resistance water heater. You will never, ever, want to use this type when using the performance method of compliance. Occasionally, if you’re trying to grandfather in some unpermitted basement addition, guest cottage, or in-law unit, and the space qualifies for prescriptive (not too much glazing!) you might be able to get away with stating “existing systems to remain” and bypass the issue. But that’s about it.
• Electric Heat Pump. I’ve never had to model this type of water heater, so I can’t speak to it. I don’t think the penalty is as steep for this type as for the electric storage.

Hot Water for Additions. If we run an addition as “Addition Alone”, water heating is not calculated. However, if the addition won’t pass by itself and we have to model the whole house, then the water heater becomes a potential source of energy trade-off. It’s even more important for additions and partial remodels, because other interventions such as upping all the wall insulation may not be available with projects of limited scope.

Pools and Spas. These are not included in the energy report calculations. There are separate energy standards that apply to them. For now, they are outside the scope of this article.

A Nifty Search Lookup for Current Models

Miles Hancock, one of our Green Compliance Plus Affiliates, walked me through the Appliance Efficiency search database on the California Energy Center’s web site. This database contains listings for all appliances certified to the California Energy Commission as meeting currently applicable efficiency standards – so it won’t be of much use for legacy systems (for remodels or additions). Some of the terms they use for efficiency are different from what’s described in the preceding article, but I’ve tried to list their equivalents above, where possible.

The California Energy Center's Appliance Efficiency search database lets you find the rated efficiencies of all models that meet current energy standards.

California’s Green Building code went into effect this last January, and recently we had questions from another residential designer about CALGreen – how’s it different from GreenPoint Rating, how does it fit in with Title 24 energy standards, how it works. To answer his questions, I read through the code manual. In addition to the CALGreen code book itself, there’s a very handy cheat sheet that compares CALGreen, GreenPoints, and LEED, for low-rise residential projects. (This version’s probably a little out of date, being from 2010, but you get the idea.) The Q&A below is based partly on that conversation, with special thanks to Doug Hensel of the California Department of Housing and Community Development, who reviewed a draft of this article.

What is the intention of CALGreen?

To reduce environmental impact through better planning, design and construction practices. CALGreen addresses energy, water, material use, and environmental quality (mainly indoor toxicity and comfort).

How is CALGreen structured?

CALGreen is organized into chapters for residential and non-residential buildings. Within each of these, there are mandatory measures that apply  statewide, and voluntary measures, that can be adopted by local building departments.

• Mandatory measures, in Chapters 4 and 5, apply to everyone statewide
• Voluntary measures, located in the Appendices, have two tiers with prerequisite and elective measures
  • Tier 1 Prerequisites are a grouping of measures which set the base for that tier.
  • Tier 2 Prerequisites include all of Tier 1, plus some enhanced or additional measures.
  • Electives are an a la carte collection of additional measures not included elsewhere.

Each tier lists additional prerequisite measures that are mandatory in order to achieve that tier, plus a specified minimum number of electives. Sounds complicated, but it does allow for more flexibility.

California's new Green Building code, which went into effect this past January, has a flexible, multi-tiered approach with both mandatory and elective measures.

What is the rationale behind CALGreen’s tiered requirements?

Voluntary tiers are just that: voluntary. Local authorities can adopt these tiers, thus making them mandatory – in that location only. There’s a note that local building officials can grant exemptions to these tiers in individual cases, in the case of “practical difficulties”. The tier concept was developed in order to allow some of the more progressive jurisdictions to go beyond the code minimum, while still maintaining a level of consistency throughout the state.

What parties, interests, or types of experts were involved in CALGreen’s creation and formulation?

Participants and stakeholders include various California state agencies, as well as model code organizations, building officials, and representatives from the construction industry, the environmental community, the green building industry, and the design community.  BuildItGreen, the private consortium that came up with the GreenPoint Rated system, is not named as a contributor to CALGreen in the official code book, but it can’t be coincidence that many measures are almost identical between GreenPoints and CALGreen.

Who owns CALGreen?

CALGreen is published by the Building Standards Commission, although they don’t determine all of the content by themselves. For residential projects, the CA Department of Housing and Community Development has the primary role in developing the regulations. Various other agencies are charged with determining CALGreen requirements based on the type of occupancy. The Building Standards Commission has the primary role in developing the green building regulations for non-residential projects with the exception of certain types of buildings such as public schools and hospitals.

How does CALGreen fit into other code requirements?

CALGreen goes along with all the other California building codes and standards: Building, Electrical, Mechanical, Plumbing, Fire, and Energy. Apparently CALGreen trumps them in places where they might differ. In general “the most restrictive requirements shall prevail.” Similar to these other codes, local agencies have a lot of freedom to make specific amendments to the CALGreen code – those amendments apply only within that jurisdiction.

Is CALGreen now mandatory everywhere in CA? Are there guidelines for its applicability to different types of projects (eg remodels vs new construction, etc)?

Yes, it’s now the law. Applicability is by major type of construction, for example low-rise residential vs hospital. Both the HCD and the BSC have guidelines on their web sites providing further assistance.

Are there special certified CALGreen consultants who help homeowners and designers plan ahead on their design projects? What is their methodology?

The International Code Council (ICC) offers certification exams for CALGreen. There’s also a group called CALGreen Training which appears to be a private organization. I don’t think the latter training results in “certified” anything (which would involve a test), but there’s a Certificate of Completion. Training can be delivered online, through webinars, or in person. Their page of Helpful Info is quite informative.

How will CALGreen be enforced? I see things like “Construction Materials Protected From Moisture Damage” which means frequent site inspections during construction. Who is in charge of enforcing it, and at what points in the project?

Local building officials and inspectors.

How does Title 24 energy compliance fit into CALGreen?

California’s “green building” code goes beyond energy performance to encompass all sorts of things like reduced construction waste, water conservation, non-toxic sealants, renewable materials, etc. By contrast the California energy standard (also known as Title 24, Part 6) is primarily on promoting more energy-efficient buildings, and only considers the fixed infrastructure: building envelope, heating and cooling, water heating, some lighting restrictions. So it’s more limited in scope than “green building” or “sustainability”. It’s one thing for a design client to say “I want it to be green” and quite another for them to decide HOW that will be accomplished. Creating energy-efficient buildings is part of green building, but green building encompasses a lot more than direct energy usage.

One thing to note about CALGreen is that the upper tiers insist on exceeding Title 24 by either 15% or 30%. That can be a huge “gotcha” if your house has a lot of glass.

These levels coincide with other energy incentives that are currently available. In any case, don’t wait until the day before submittal to run your Title 24 report. In order to beat Title 24 at all, you have to use the energy modeling method – which asks for specifics about things like mechanical systems, windows, and insulation. Beating Title 24 is getting harder and harder, often requiring additional tests and material substitutions. It’s not last-minute stuff.

Why does CALGreen want 15% over Title 24? Isn’t Title 24 already the code? How can a code require exceeding the code?

You will need a MENSA level IQ to understand the reasoning, but it looks like the California Energy Commission and the Department of Housing and Community Development are quibbling over the meaning of “green building”. So, CALGreen says meet Title 24, but the CEC (which develops the California energy code) thinks that the term “green building” should only apply to buildings that exceed Title 24 by 15% or more.

When people ask me how a building code can exceed itself, I feel like I need a MENSA-level IQ. Suffice it to say that different parts of the same overall building code can differ.

Another example of “code that exceeds the code” is water use. CALGreen has a mandatory measure saying that residential water use has to be 20% below the maximum allowable by the California Building Standards Code. It’s enough to drive one mad. The good news is that there will more work for code consultants, potentially reducing unemployment.

How do the following agencies (BSC, HCD, and CEC) interact in terms of exerting authority? Is one a subsidiary of the other or are they independent agencies?

State agencies are given various authorities by the California legislature. Similar to laws of Congress – once that law is passed, it’s out of the hands of the lawmakers, the mandate goes into the hands of the state agencies to interpret, then implement, this mandate. Then, local government enforces it. For CALGreen, local officials review the code to make determinations for each specific project and circumstance. Energy efficiency is a subsidiary or detail portion under overall CALGreen, but neither the Department of Housing and Community Development nor the Building Standards Commission has the authority to set mandatory energy policy in California. The CALGreen code doesn’t spell out the energy standards in detail; that is deferred to the California Energy Center. However, the BSC must approve all energy regulations adopted by the CEC prior to publication.

Do the residential requirements apply to remodels?

No. CALGreen only applies to newly constructed buildings. The definition of “newly constructed” does not include additions, alterations, or repairs.

How was it determined which items ended up in the CALGreen code and which were omitted?

The overall approach is to make it incremental, but state the long-term goals as well. This gives people a chance to learn the new ways and adapt, but they can see farther ahead and go beyond the requirements if they want.

Yesterday's futurism leads to today's advances. The bathysphere on the left was used in 1930 to descend around 3,000 feet - the deepest at that time. Now, deep sea scientists are entering even more extreme environments, allowing creatures like this deep sea isopod on the right and even deep-sea vents at the bottom of the ocean to be observed and captured on film.

Today’s futuristic dream is tomorrow’s baseline. For example, the CEC has a goal of all new homes being Net Zero by 2030. If you tried to enforce that one today, no one would be ready – costs would be prohibitive, and there would be a shortage of qualified designers and builders with the know-how to make it work. But, by incrementally tightening energy requirements, it gives time for new solutions and methods to be developed and tested.

Are there requirements for habitat conservation?

One area that seems to be omitted from CALGreen, and largely from GreenPoints as well, is overall habitat conservation where the natural state of the site is left pristine and undisturbed, as in a nature preserve. This would fall under construction (to build carefully and not destroy any more habitat than was necessary) and also under site planning. The closest both these systems come is a topsoil conservation feature, and some items about low-water landscaping with native species. GreenPoints does have points for unspecified “innovations”.

CALGreen says that it doesn’t want to restrict innovation, but there are no specifics. I think they’re deferring detailed habitat rules to local jurisdictions. CALGreen does have a completely voluntary site selection guideline encouraging the re-use of previously developed sites, which would promote the same goals.

What is the difference between CALGreen and GreenPoints?

CALGreen is a mandatory code, and it’s statewide law, with mandatory measures and additional prerequisites by tier. GreenPoints is 100% voluntary, unless a local jurisdiction decides to require it. The concept of “GreenPoint Rated” doesn’t exist in CALGreen. There’s no such thing as “CALGreen Rated”. Either you meet the requirements set forth in CALGreen at the level set by your local authority, or you don’t.

GreenPoint Rating encourages a project to achieve the highest score possible through the inclusion of a mostly voluntary list of electives. There are a few “required” items, but most of it’s discretionary. A local jurisdiction can require all projects to be GreenPoint Rated, and to meet a minimum score, but they usually don’t say beyond that which electives you must use. This allows a lot of flexibility.

The idea of GreenPoint Rating is that there’s some level of follow-up during construction by a certified independent GreenPoint Rater to verify that the measures are being followed correctly. In fact, you can’t complete the rating process until the house is completed. This makes the score more credible. CALGreen requirements, like other code requirements, are enforced by local building authorities at various points in the project: permit submittal, various inspections during construction for things like foundation, electrical, and final inspection.

Both GreenPoint Rating and CALGreen could be used during initial planning stages as an idea generator for someone who wanted a “green” project but didn’t know how to go about it. It seems that GreenPoints would be a little better for this – it goes more beyond the minimum, and is more specific in some areas, particularly landscaping. Working directly with a GreenPoint Rater as a consultant during initial planning stages can help identify which GreenPoint features are most acceptable, desirable, and feasible.

The GreenPoint Rated system is a bit more specific about water conservation measures available for landscaping. It's not only water use, but whether plants are "native" that counts.

We haven’t mentioned LEED that much, but the LEED certification process also involves a special LEED certified consultant. It’s been criticized as being too expensive and cumbersome for single family residential projects. GreenPoints does add some cost for the consultant, but it’s a lot more reasonable.

Why do we need CALGreen if we already have GreenPoints, or vice versa?

Good question, especially if you’re building in a town that requires both GreenPoint Rating and some of the CALGreen voluntary tiers. I would guess that GreenPoint Rating was a bit quicker to develop, not being so encumbered by bureaucratic process, and it served as a warm-up to incent people to move ahead. GreenPoints is a good road map – the measures are simpler to understand, and clearly written.

Doug Hensel of the HCD rephrased this a bit more diplomatically, “CALGreen is mandatory in all cities and counties, and will thus capture many more buildings than GreenPoints alone. Contrary to GreenPoints, CALGreen is developed using protocols set forth in the Building Standards Law, which require an open and transparent process of public vetting and participation.”

How can a designer or homeowner reduce confusion if their project requires both CALGreen and GreenPoint Rating?

Best thing would be to work with a consultant who’s got dual credentials in both CALGreen training and as a GreenPoint Rater, and involve this person early in the project. They’re not the project manager, though. That would probably be either the owner, the designer (if used), or the builder.

Selecting a good builder is important – and not just going with the lowest cost bidder, either. Get someone who’s already bothered to get a Green Builder certification without being forced into it. If the project involves a licensed architect, the architect should also be familiar enough with local codes to stay within them. It helps if the major parties are already experienced with local issues, including working with the local building department.

How does the energy standard set forth in Title 24 fit into GreenPoint Rating?

GreenPoint Rating also has a mandatory requirement of exceeding Title 24 by 15% or more. Local authorities seem to have two levels of GreenPoint adoption. The first level requires a GreenPoint Checklist at submittal time, showing which features are included in the design. It’s for informational purposes only. The second level requires full GreenPoint Rating, and sometimes a minimum GreenPoint score. This is harder to do, and involves a lot of verifications – including beating Title 24 by 15%.

Again, plan ahead – check with the local building department that has authority over the project, and find out what all their green requirements are. Are they requiring any CALGreen tiers above the mandatory minimums? Are they using the GreenPoint Checklist? Do they require each project to be fully GreenPoint Rated? Do these requirements apply differently based on the project itself, i.e, its size? What other green building requirements do they have? There is no escape from reading the fine print, but we hope that it’ll make a bit more sense now, after reading this article.

Epilogue

I’d sent a draft of this article to Doug Hensel at the Department of Housing and Community Development for comment, not really expecting any response, but he called me right away and sent me a commented version. I incorporated most of his comments (but kept the comment about bureaucracy). He also pointed me to the page containing ALL the CALGreen documents: the CALGreen code itself, a user-friendly guide to CALGreen for low-rise residential buildings, and a slew of CALGreen compliance forms and worksheets for everything from construction waste management to finish flooring materials.

Remember last week, when we were talking about glass houses? Well, here’s another Title 24 case study on a 4,500 SF house, also from Swatt|Miers Architects. This house had almost 60% glazing to floor area, much of it custom built on site: 564 square feet of single paned butt glazed corner windows, 540 square feet of frameless glazing, a steel framed window, a 30 foot tall translucent window in a stair tower, 300 square feet of skylights, and a custom built wood screen interspersed with glass panels. That’s almost 2,700 square feet of glass.

And, to make the challenge that much more… piquant… it was in California climate zone 2 (Sonoma – HOT)… AND, they needed to beat California’s Title 24 energy standard by 15% because of local ordinances. It was the combination of all that single glazed area with the climate zone that concerned us the most. But, we had a reputation to maintain, and our motto to designers was, “We’ll never tell you that you have to shrink your windows.”

(Above image courtesy Swatt|Miers Architects.)

Well, we did end up telling them that they would have to find a way to make the butt glazing work with double panes (which we described in our article on window performance). So I suppose now we have broken our cardinal rule of never impacting the visible design.

Complex Shapes

Although the design was entirely based on rectangular planes, the volumes didn’t always line up one stacked directly over the other. This meant that there were some extra floor and roof areas to account for, and there were some subtle variations in building height, too. Most of the time, this can be generalized, but in this case we wanted to be as exact with every surface area as we could, so that we could claim the maximum thermal mass credit. I knew the planners might be reviewing the report against the drawings with a fine-toothed comb, and we needed to be prepared to respond to any comments with a solid grasp of facts.

Wood framed overhanging floor areas were modeled separately from the slab flooring on the main level.

Start at the Beginning, Grasshopper

As we mentioned in the previous case study, we try to start at a basic level with whatever systems information we have from the designer, and then work up from there. The main heating system was radiant, with A/C. On the plus side, the design called for slab flooring, with gypcrete on the upper level – this thermal mass gave us a ray of hope. Even so, the first trial was dismal. 73% below the standard. Heating was missing by 75% and cooling was missing by a whopping -136%. Only pride kept me from throwing in the towel – pride and curiosity.

“Patience, Grasshopper,” I said to myself. “Just do what you usually do, and don’t say anything until you have some good news to report.” So, here’s what we did, and what worked the best.

Cool Roof/Radiant Barrier. Although this seems like a minor place to start, we’d have to try a cool roof at some point, and it might actually help in Sonoma. The cool roof did make a difference (down to -67%), although the cooling improvements were offset by a small detriment on the heating side. What we really needed was a selectively cool roof, that changes color based on outside temperature – maybe someday soon there will be such a thing. The radiant barrier helped less, and they would have had to change the roof construction to include it. The gains from the barrier didn’t justify including it – unless we absolutely had to.

Wall insulation. Next, we upped the wall insulation from the requisite R13 to R21. That pushed us from -67% to -55%. Pretty good, but still way behind. The designer had thoughtfully provided us with the wall assemblies, so we knew that the cavities were 2 x 6 – large enough to fit R21.

The designer provided us with complete details, which helped us to ascertain how much insulation we could specify in the energy model. Image courtesy Swatt|Miers Architects.

Ducts. There would be both heating and cooling ducts in this project. Although the main heating system was radiant, there would be a forced air backup. We couldn’t model both systems, but we had to keep the heating ducts in the energy model, which cost us. We did verify with the designer that the ducts would be located within conditioned space, which gave a credit. And, we added the HERS test for duct leakage, which brought us from -55% to -40%. (Actually, we tried eliminating the heating ducts and it didn’t help as much as it had on other projects.)

Blower Door Test. With heating and cooling ducts within conditioned space and the duct test taking us to -40%, we added another HERS test – the blower door test, which measures the airtightness of the entire home. Doing these HERS tests on a sizeable house such as this was bound to be challenging, so we stressed to the designer that they, and their builder, should read our article on HERS tests so that they knew what was involved. The builder in particular would need to know that the project was required to pass these tests. The blower door took us from -40% to -37%, not that much. Well, we’d keep it in for now, since it was looking like we’d need every last inch of compliance.

A/C Verifications. Next, we tried adding the HERS tests that apply to air conditioning systems: test for refrigerant charge, airflow, fan watt draw. These took us from -37% to -32%. I had hoped for more. We tried upping the A/C SEER from the standard 13 up to 18 SEER, which, together with the HERS tests, brought us to -29.5%. One thing to note is that often, the HERS tests have more of an impact on compliance than simply upping the SEER. But, all of this was simply postponing the day of reckoning, which was to attack the windows.

Window Performance

As with the other Swatt|Miers case study, we divided up all the window areas by type: Butt glazed corners, frameless wall insets, the stair tower, the custom steel window, various sliding pocket doors, operable casements, the 40 foot long wood screen window on the upper gallery, and the skylights. The design called for various overhangs, including a large canopy extending over the main house and a separate guest house. Most of the window framing was metal, which is not as good an insulator as wood.

Initially, I used the performance specs from Efficient Windows as a starting point for estimating all the custom areas, assuming that all windows with the exception of the corner butt glazing would be double paned, low e glass. There was a lot of back and forth with the designer to establish the composition and construction of the various custom windows. We couldn’t go any better than the standard on most of these (we were lucky to get the standard). The casements and the sliding pocket doors were Fleetwood window products, with numbers that we could look up.

I asked around and searched for information on whether any sort of single glazed window could ever be “high performing”. Alas, there was no magic glass. The experts all informed me that the main factor in window performance is 1) multiple panes with insulating layers of air or gas fill 2) airtightness of the frame itself and 3) insulating properties of the framing material. There was no such thing as a thermally  broken, metal framed window with single glazing, because why? There wouldn’t be any demand for it.

But we were still at -29%. Something had to give. So, I broke our rule and made all those butt glazed corner windows double glazed. That took us to -11%. And then, I modeled the Fleetwood windows using the best numbers they had available for each type. That took us to -6%. At the same time, I put out the word to see if anyone had successfully built a corner glazed window with double paned glass, because I knew that the designer really wanted to keep that transparent appearance, and putting a spacer bar on the corners would be a major disappointment, to say the least.

And it still wasn’t enough. Even adding the dreaded QII test (a HERS test where every bit of insulation is inspected as it’s installed during construction) wasn’t enough, although the QII did bring us from -11% to -0.8%. So close – and yet not close enough, considering that we had another 15% to go.

Interior Mass Surfaces

At this point I dragged Mark English over and made him review the entire drawing set plus all the details. As an experienced architect who’s been designing and building homes for 25 years, I figured he’d see a few things that I had missed, and he would make sure we didn’t take too many liberties with the wall and roof cavities.

Based on consultations with Mark and numerous exchanges with the designer to verify the exact location of every wall and floor finish, we added the thermal mass of a dramatic 2-story stone veneer wall, over 1475 SF of thermal mass. Additionally we included all the tile flooring in the bathrooms, countertops, and the gypcrete from the second floor’s suspended slab floor. Even though this floor was largely covered by wood or carpet, it still yielded some credit. That took us from -0.8% to +12%.

Upon our request, the designer provided us with the location of vertical thermal mass surfaces - stone veneer walls - which we could then include in the energy model. Image courtesy Swatt|Miers Architects.

And it still wasn’t quite enough. I felt like a magician reaching into a hat for another rabbit and coming up with a hamster instead.

What the Designer Said

I figured it was time to fill in the designer with our progress to date, and test the waters about making the butt glazed windows double paned. It might be a good time to insist on an uber-efficient water heater. We’d actually started with a reasonably efficient one, a .80 energy factor, but without further information, I was hesitant to commit to anything extreme. Eventually we would have to include the actual models they were using, and there would likely be more than one with a house that size anyway. I don’t think they had worked out the mechanical systems to that detail, so now was a great time to test and suggest a few things.

But before we reached into our top hat for that last rabbit (the water heater itself), we tried a few more things just to see what would happen.

Solar water heating credit. The design hadn’t specified solar equipment of any kind. Well so what? Maybe it would let them keep that single glazing, although I doubted that.  Even though there’s no credit for the use of renewable energy for electricity or heat, there is Title 24 credit for solar hot water. It’s based on the percentage of hot water that the home is expected to get from solar, and sure enough, set this percentage high enough and the compliance score improved.  So, by pushing this number to an unrealistically high 50% we were able to inch our compliance from +12% over to 17% over, although I doubted that this would actually work.

And why not? Well, the problem with it is that you still need some kind of indirect storage tank to ensure hot water in the evening, unless you only plan to shower at high noon. In addition, this home would have extra water heating demand because of the radiant heating. But hey… we reached our goal, in theory at least.

Higher Solar Heat Gain on Some Windows

On the last case study, I had, purely out of curiosity, tested a series of window performance combinations just to see what would happen. Although a low U value window was always the best choice, because it provided thermal insulation for both hot and cold temperatures, what could we do if the best U value we could find was average – if that? Since we had so many custom windows that would be built in the field, we couldn’t make aggressive assumptions about them.

So, I inched up just the solar heat gain on the Fleetwood windows, while keeping the U value the same. This would allow at least some glazing areas to keep up their insulating value, while allowing a little more solar heat. Although originally the design had lagged more on cooling, it was now the heating side that had all the shortfall. We were actually ahead on cooling. This latest change brought us from 17% over to 18% over, so it didn’t make a huge difference. Heating was better, cooling lost a bit.

Skylights

The skylights were another big unknown. There were a lot of them, and the designer indicated they didn’t want wood framed because they were concerned about leaks and such. Then they selected a manufacturer who actually had pretty good numbers, which brought us from +18% to +21% over.

Highest Efficiency Boiler

It was time to pull out our very last rabbit, which was to boost the water heater performance as far as it would go. By specifying a boiler with a 95% efficiency, and keeping a solar hot water credit at 25% (still probably too aggressive), we got the house to exceed Title 24 by 32%. At this point, we dialed back the Fleetwood windows to the actual numbers (Westwood and Norwood product lines, dual glazed low E, thermally broken, but no argon – air fill), and removed the solar hot water credit altogether. We kept the HERS testing for credits: the three A/C tests and the duct test.

The final score? It came out as exceeding Title 24 by 25%. This would give them a little margin if by some chance it didn’t pass every HERS test. Some of those tests were worth GreenPoints, too. So, chances are this house will earn a respectable GreenPoint Rated score as well once construction is complete.

A few final notes follow, on what the designer did to help us, and a note on modeling multiple zones.

Detailed Wall and Floor Assemblies

This was one of the few projects where the designer provided us with detailed wall and floor assemblies, 3 drawing sheets of it. This was great, because we could see exactly where the gypcrete was, which portions of the floor were covered (and with what) and which walls had interior stone veneers.

Although we don't always have to model every layer in the floor, in some cases it helps to know exactly what's in there. Image courtesy Swatt|Miers Architects.

Modeling Multiple Heating and Cooling Zones

This was something that we would have resorted to only at gunpoint, because it’s very time-consuming. Essentially, you model each zone as a separate volume – including floors, walls, and ceilings – as if it were its own little house. Title 24 gives credit for this, but I’ve only ever done it once on a private home, and we had no way of knowing how much it would help unless we tried it.

Actually the real question is whether an all-glass pavilion can still comply with the new version of California’s Title 24 energy code. Although Title 24 has been around since the 1970s, it is only now that designers are feeling the pinch. Given the increasing strictness of the energy code, what can an architect do if he (or she) wants to create designs with dramatic glass curtain walls?

The “glass house” shown on the cover image is, of course, Philip Johnson’s famous Modernist masterpiece, also called the Glass House. Even that house could, with the right high-performing window system, comply with Title 24 requirements – I tested it out. But, let’s talk about some more current designs for our case study.

When we got our first Title 24 project from Swatt|Miers Architects, I didn’t really know if we’d be able to finesse it. We had never had a project quite like it before. But then I remember seeing an award-winning Net Zero home in Truro, Massachusetts (by Zero Energy Design) which had acres of glass everywhere. If they could make it work in a cold place like Massachusetts, surely we could do the same in California!

This Net Zero home in Truro, Massachusetts, was designed by Zero Energy Design. And yet, this house still manages to be efficient even with all this glass. Photos: Eric Roth.

Our first Title 24 project from Swatt|Miers Architects was a 6,000 SF all-glass pavilion with a generous roof,  a custom window wall on one side, and heated slab floors. On the plus side, the roof included large shading overhangs, and we had ample time and flexibility to select high-efficiency heating and water heating systems. There were no large skylights or ductwork to worry about, either. The house was located in a moderate climate zone, so they weren’t even going to install any cooling systems at all.

Another big plus was they didn’t have any “beyond compliance” goals such as GreenPoints. So, we didn’t have to beat the standard by 15% or more. As you’ll see in a minute, that would have been possible, but very expensive.

On the challenge side, there was almost 5,000 square feet of glazing – 75% of the conditioned floor area. In addition, the design called for metal framed windows, which are inherently less efficient than windows framed in wood or vinyl. Even thermally broken metal windows can’t always match the performance of wood.

This house had 75% glazing to floor area and yet, it still managed to comply with California's Title 24 energy requirements. Design Courtesy Swatt|Miers Architects.

Strategy: Start Low, Increment Up

We usually start by running each project with baseline assumptions, usually the same ones used for the prescriptive Title 24 method. The Title 24 prescriptive method sets forth minimum requirements for things like heating and cooling performance, insulation levels, maximum allowable glazing areas, and window performance – but it’s all or nothing. Either you meet every requirement, or you have to use the performance modeling method to satisfy Title 24. The software model has some built-in generic inputs for things like water heaters that also assumes a very basic level of compliance.

Using the software modeling method of Title 24 energy compliance, a house can fall below the standard in one area as long as it makes up for that shortfall in another area.

In this case, the first trial missed by -76%, with shortfalls on heating and water heating. Surprisingly, cooling was not a problem – at least, not in the model. Still -76% seems like a big, scary number – one which we attacked incrementally.

Preliminary Trials with Insulation and Water Heating

Increasing insulation levels from R13 to R21 brought it to -67%. There wasn’t that much wall to work with, the walls being mostly glass, which is measured by window performance rather than insulation. The roof already had plenty of insulation, and adding more past a certain point had a negligible impact.

Just as a test, adding an overhang over the South window wall (which didn’t have one) actually made it worse! That’s one thing about trade-offs. Sometimes a measure that helps with cooling will create more load on the heating side, and heating was what we needed to fix. But this design didn’t specify an overhang there, and even when there are overhangs, modeling them is optional.

Next, we tried upping the water heater performance. Originally we’d specified a generic setting, because the mech hadn’t been worked out yet. For a house this size, over 6,000 SF, you probably wouldn’t have a single heater anyway, and you definitely wouldn’t be running all the hot water AND the radiant through one heater. So we had started with a 75 gallon storage tank with a .75 energy factor – legacy numbers.

A tankless heater with a storage tank, with 2 separate systems, and a higher energy factor, got us down to only -49% below Title 24 requirements.

Main Trials: Windows

But all this was simply prep, because the windows were going to be the biggest challenge. The window performance factors that are important for Title 24 are the U value, which measures thermal performance (keeps winter heat in), and the Solar Heat Gain Coefficient (keeps summer sun’s heat out). We had all been thinking that with all that glass, cooling would be the concern, and we’d have to get the lowest SHGC we could find. Not so. It was the U factor on all those windows that would make or break our compliance.

In fact, having a higher SHGC might help because we could afford to lose some cooling margin if the solar heat gain would actually help on the heating side. Passive solar designs in far North latitudes try to leverage the sun’s heat, especially in the wintertime when there’s so much less of it. We don’t normally think that way in California, but occasionally a higher SHGC can actually help, especially on the East wall. The reasoning is that solar energy on the east, when the sun is just rising, can help the house to recover from cooler nighttime temperatures.

Typical test results from Fleetwood Windows, available online, show just how many options there can be even within one product line.

The Title 24 prescriptive minimum for window performance is .40 U/.35 SHGC, lower being better for both these numbers. That’s pretty tough, considering that most ordinary metal framed windows run around .50 or .60 U factor, even for double glazed, “Low E” glass. We had started with the generic “metal double glazed low e” input which is around .65/.40. This project specified Fleetwood windows, which has several product lines with a wide array of options for glazing, thermal breaks, gas fills, and even glass types. All of their test results are easy to find, too.

We also modeled each window opening separately (over 77 of them), so that we could use different performance numbers for each window type: there were Casements, Awnings, Fixed, Sliding, and a couple of custom settings. That way if a better performance could be had from the fixed windows but not from the operable ones, we could include it. Sometimes clients have also asked us to use different settings for different cardinal directions, for example, using a more expensive but spectrally selective glass on a western or southern wall where it might matter the most.

For the Swatt|Miers design, Green Compliance Plus modeled over 70 different glazing areas in order to account for small performance variations among window types.

U Factor or SHGC – Which Is More Important?

Although we were more concerned with the U factor, it was possible that testing different combinations of U and SHGC factors might yield some interesting information. So, we spent a lot of time trying very low U/low SHGC combinations. We also tried some average U with very high SHGC windows, as well as trials where we kept one number the same and varying the other one up and down to see what would happen.

A low U factor was the best choice, regardless of SHGC – but, this might not be achievable, even if they used the more expensive, thermally broken frames. Of course, triple glazing with argon gas fill would help a lot, too – I’m not sure what the quote was for 4,500 square feet of windows with triple glazing/argon/thermal breaks, but it would have killed the project budget. We had to find some way to make it work with double glazing.

A U value of .35 or under would be better overall. A U value of .25 would be awesome. If the U value was low enough, like .30, it didn’t matter as much what the SHGC was. In fact, with a U value of .25 some of the runs came out almost 40% over compliance! Some interesting window results: With a higher U value, a moderate solar heat gain acted to compensate somewhat for heating loss. It was almost as if there existed a second, smaller “peak” of outliers which, if I had a lot more time, I’d try to graph in more detail.

Of course, it’s all very well to say that we need a window with a U value under .30. The U value was the one thing that most limited us, because with the window products and framing materials selected, it simply wasn’t possible or cost-effective to get down that low. And, specifying an artificially high SHGC just to “make the numbers” didn’t make sense. But then again, neither did specifying triple glazed, argon filled windows in a mild California climate zone.

Custom Window Wall

The custom window wall on the South wall was another challenge. Fortunately, this area was wood framed – not aluminum like the rest of the windows. The wood framing would help with thermal performance, and the plans already called for double glazing with Low E glass. However, since there were no formal NFRC test results for it, what numbers could we safely assume for performance? As it turns out, we checked with the local Planning department for the project’s location, and they indicated that using the Title 24 prescriptive standard, .40 U/.35 SHGC, would be acceptable. This standard already assumes a wood framed, double glazed, low E glass window – so it made sense to use it for the custom window areas.

We might not be so lucky in another jurisdiction, though. The plan checkers have some leeway to use their own judgment and, if we’d been in another area, we could have been asked a lot more questions about materials, glass types, etc. – and possibly we might have had to use less forgiving numbers.

Additional Measures

In the actual project, we tried a few more things. One was a super-efficient water heater. Most water heaters are in the .65-.80 range for energy efficiency, but there are some out there that go almost to .95, so by creatively assuming that they would use the best systems available, we could at least present that as an option for compliance.

We called out each area of interior exposed thermal mass – exposed stone, tile, and concrete – because usually this helps with Title 24 calculations.

And, as a last resort, we could have called for some HERS verifications for extra compliance credit. Our article on HERS testing describes each of these tests in detail: duct blaster, blower door, QII, and various tests on the A/C system. Of course, not all these tests were available on this project. With radiant heating and no A/C, there were no ducts to test. And, the various A/C tests – refrigerant charge, fan watt draw, airflow, and verified EER – couldn’t be used, either.

Would Cooling Be an Issue in the Real World?

Initially we were surprised that cooling was not a problem, and we were all wondering how realistic that would be once the house was actually built and inhabited. Title 24 intentionally ignores some real-world conditions such as landforms and shade trees, but it does apply location-specific climate data on top of the broader “climate zone” designation. The designer expressed concern that with a high SHGC window, the house would be too warm during the summer, especially along the South side. And really, to us it didn’t make sense to use an artificially obtained number when the most straightforward thing to do would be to use California standard Low-E, low SHGC glazing.

Would Philip Johnson’s Glass House Meet Title 24 Energy Requirements?

Just for fun, I did a quick test of Philip Johnson’s Glass House, using floor plans and dimensions that I was able to find on Google… no guarantees on accuracy, but it seemed like it was worth a try. The trials included three California climate zones: Woodside (Zone 3), Tahoe (Zone 16) and Livermore (Zone 2) and a few compass orientations for 0, 45, and 90. For starters, I assumed double glazing and Low E glass, with the same numbers as a wood frame would be. And, for heating I assumed radiant heated slab flooring… which I think is the actual method.

Title 24 ignores shade trees, which in the case of Philip Johnson's Glass House are a major environmental feature.

The compass orientation didn’t matter that much – it mattered a little – but, the location had a bigger effect, mainly in the balance between the shortfalls between heating and cooling. No surprise, Livermore had the biggest cooling problem initially.

Setting the glazing to something more like the actual (metal framing, clear glazing) was disastrous for Title 24 compliance. However, when I changed the windows to the “best available” performance numbers – something around .20 U/.20 SHGC – the house complied in all three zones without any further changes.

I've never been inside the actual Glass House. I wonder how comfortable it really is in the winter? There are almost no wintertime images of it.

The Catch – Custom Built Windows Can’t Use NFRC Test Results

In reality, it may not be possible to even obtain pre-manufactured windows of the size that are used in Johnson’s Glass House. And, in order for performance numbers to be valid and acceptable for Title 24, the window units have to be NFRC rated. We’ve discussed this in a previous article, so I can’t assume that the Glass House design as it is now would ever be able to fully comply with Title 24. And, of course, the Title 24 modeling software only has climate data for California, not Connecticut where the house is actually located. Nonetheless, it could comply a lot more easily than some other projects we’ve worked on.

Another Glass House: Olson Kundig’s Glass Farmhouse

As I was looking around for any accounts of the actual comfort of Johnson’s Glass House, I found another, much more recent take on the all-glass house from Olson Kundig Architects, located in Oregon. Alas, no reports on actual energy use or comfort here, either – but Kundig did employ solar design features and high-performing glass and took some care to adapt the house to the local climate. You can see some nice images and a description at The Contemporist.

Many architects have yet to realize how much a window’s energy performance can impact their projects, especially under the new Title 24 energy code. Ordinary glass is great at letting in daylight but it’s a terrible insulator. It also does little to block the sun’s heat in the summertime. Windows lose heat through the glass, and they can also leak air around the edges of the frame.

Here are a few analogies to understand the different ways that windows can lose both heating and cooling energy. If you wear a big holey sweater in the wind, it doesn’t keep you very warm. That’s air leakage. Now, imagine just wearing a single sheet of clear plastic on a winter day. It’s a better windbreaker than that holey sweater, but you’ll still feel pretty darn cold. That’s because a thin sheet of plastic, like a single sheet of glass, is a poor insulator. And remember what happens to your car parked in the summer sun? It gets 20 degrees hotter than the outside, or more – if you have black vinyl seats, you’ll scream when you sit on them in your summer shorts. That’s solar heat gain.

When it comes to efficient windows, it's the entire window unit that matters, especially for air leakage. To understand the importance of air flow on energy needs, think of a sweater as your own personal "building envelope". Wool is a great insulator, but not if it's a holey sweater worn outdoors on a windy day.

Windows Lose More Energy Than Solid Walls

The more windows a house has, the more energy that house will require for both heating and cooling. And if those windows are on the South or West side of the house in direct sun, they can turn the home into a summertime toaster oven.

Windows can leak energy in several ways:

• Air leakage through and around the frame
• Heat transfer directly through the glass
• Thermal bridging through the frame, especially with metal frames
• Radiant heat from direct sunlight

Which building will be easier to heat in winter and cool in the summer, the saltbox on the left with modestly sized window openings, or the all-glass modern office building on the right?

What Kind of Windows Are More Energy-Efficient?

Title 24 requires that windows meet minimum performance standards. Most legacy windows don’t meet this standard, and a lot of fancy metal-framed windows don’t meet it, either, due to metal’s heat conductivity. There are metal windows that meet the Title 24 standard, if you’re willing to pay for triple-glazing, thermally broken frames, and argon gas fill. For a large house that’s got acres of glass, this is very expensive and it’s really overkill, too, in mild California. If you don’t want to break the bank, you’ll have to make it up with additional energy measures elsewhere.

By blocking infrared radiation, low-emissivity glass works both to keep the Sun's heat out, and indoor heat in.

There are many ways to make windows more energy-efficient:

• Special “low-e” glass that blocks solar heat radiation without blocking visible light
• Double or even triple paned construction with air layers sandwiched between the layers of glass
• Filling that air gap with argon gas instead of regular air
• Airtight frame construction
• Use of framing materials such as wood that are less conductive of heat
• Thermally broken frames to  further limit heat loss through the frame

Metal is a good conductor of heat, which is why metal cookware works so well. But that conductivity is the last thing you want in the walls of your house. Thermal bridging is another term for this type of unintended heat loss. To prevent it, some metal window frames include thermal breaks as shown on the right.

Windows framed in stone, poured concrete, or similar material might have similar properties to a masonry wall – but they’re less common and I’ve never had to model any.

Window Placement Can Make a Difference

In a moderate northern latitude, the sun's path through the sky summer and winter traces an arc across the southern portion of the horizon. This affects the amount of sunlight that reaches windows on east, south, and west facing walls of a building.

It’s probably not news that windows on the South and West walls let in more solar heat, but let’s consider windows on each cardinal direction. (Southern hemisphere folks will have the sunniest side on the North, but let’s stick with California for the moment.)

• East facing windows receive morning sun, at a low angle. Because the house is presumed to be still cool from the night, the solar heat gain from the eastern sun can actually be helpful in warming the house in the morning.

• South facing windows receive noonday sun, at a higher angle. How high exactly depends on your latitude and the time of year. The right size overhang can block sun in the summer, but admit it in the winter. Still, large areas of South facing glazing can be a liability for cooling.

• West facing windows admit the setting sun at a lower angle, but it’s after the heat of the day when you don’t want more solar heat gain. Large areas of West facing glazing can be a cooling problem – and, shading overhangs won’t help.

• North facing windows will never experience direct sun in California. Overhangs don’t do much for shading, although they’ll still keep the rain off. However, heat loss through the glass can be more pronounced on North facing windows.

Clockwise from upper left: In the morning, the sun is lower on the eastern sky and shines into an east facing window at a low angle. By noon, the sun is higher overhead in the south (although still at an angle). The setting sun in the west again shines through any west facing window at a low angle. North facing windows will never see direct sunlight.

Overhangs and Window Shape

Overhangs help with shading on the South, but a few other design features are important too: overhead clearance and whether the window has a more horizontal or more vertical shape.

Left: When shading a tall skinny window, much of the window area is still exposed. Middle: This horizontal wall of glass is situated immediately beneath a long overhang to shade a greater proportion of the glazing area. Design by Wendell Burnette Architects. Bottom: In this recent design from Swatt|Miers Architects, the horizontal windows, deep overhangs, and reduced amount of South facing windows all helped with Title 24 energy compliance.

Measuring Window Performance

There are two, and only two measures that matter for Title 24 energy compliance: the U value and the Solar Heat Gain Coefficient (SHGC). It’s important to understand the difference between the two.

• The U value helps with heating AND cooling.
• The Solar Heat Gain Coefficient only helps with cooling.

It’s true that I often ask people whether their windows are double glazed, single glazed, and whether the frame is wood or metal. That’s just when I need to come up with generic numbers for the U/SHGC. When it comes to Title 24, these two numbers are really all that matter, and the window products have to be officially tested and rated by the National Fenestration Rating Council (NFRC). Title 24 now requires that the windows be tagged, and that this NFRC rating be etched directly onto the glass.

(There are other important window performance measures, such as visible light transmittance and also the glass’ ability to block ultraviolet rays, but those aren’t considered in Title 24 energy performance.)

U Value

U value measures rate of heat transfer through the window. Lower is better. Both the framing material and the type of glass have a big impact. A window with a U value of .40 is whole a lot better at keeping the heat in on a cold day than a window with a U value of .75. Title 24 expects a maximum U value of .40, although you can find windows with a U value of under .20. Just for comparison, an ordinary window with two panes of clear glass might have a U value of .65.

Solar Heat Gain

Solar Heat Gain Coefficient (SHGC) is about how hot the interior of the house will get on a sunny day when that window is hit by direct sunlight. The hotter it gets, the more A/C you’ll be using. Well, actually it measures the amount of solar heat coming through the window. Think infrared heat lamp. In California, lower is usually, but not always, better. Title 24 usually expects a maximum SHGC of .35.

In far Northern latitudes you might want a higher solar heat gain because you’ll want to capture more of the sun’s heat in a passive solar design – but you’d still want a low U value.

Title 24 Window Performance Standard

The Title 24 baseline standard of .40 U/.35 SHGC assumes that you’re using a wood or vinyl framed, double paned, airtight window unit with specially coated “low-emissivity” glass. It’s generally better at keeping heat in, and it also filters out some of the sun’s more heat-inducing rays. Because sunlight has a range of frequencies visible to the human eye, some frequencies of visible light transmit less heat than others. So we can now obtain spectrally selective glass that looks relatively clear, but filters out a lot of the hotter rays.

Here's why metal framed windows are a problem. Even the better products don't always meet Title 24 minimum standards.

Single, Double, Triple Glazing

We occasionally get questions about whether there’s such a thing as a high performing single glazed window, and the answer is NO. There may be some variation in the thickness of the glass panes, but that alone won’t help much, nor will having a fancier glass type help all that much either. It’s the layer of air between panes of glass that does most of the work, and if you take away this layer, you take away 90% of that window’s insulating ability.

Remember that holey sweater? Well, assuming that you’re indoors out of a draft, that sweater might do a better job of trapping a layer of air next to your skin which warms to your body temperature and helps you feel warmer in a cool room. As long as nothing strips that air away, you’ll feel warmer.

Adding layer of air helps a window's heat insulating ability. Even more so if that layer is a gas fill like argon rather than regular air. For extreme climates, triple glazing may be needed.

Getting NFRC Test Results from Window Manufacturers

What we see in our Title 24 work comes from other small design firms doing custom residential design – firms like us. The architects who come to us for Title 24 consulting care a lot more than average about aesthetics, about design integrity, and about pleasing individual client tastes.

Top: This French style home designed by Taylor Lombardo Architecture used wood frame, double glazed, low e windows to achieve a traditional look. Bottom: This Modern design from Swatt|Miers Architects specified Fleetwood aluminum framed windows for most of the glazing. The grouping in the center of the illustration is actually a custom-built window wall. Green Compliance Plus provided the Title 24 energy compliance reports for both these projects.

Some window manufacturers are really good about posting their numbers, others are not. If you’re a design-oriented architect and prefer certain styles, you might have to get used to looking at the numbers first, and the appearance second. We’d hate to have to tell you to abandon some of your favorites, but if we can’t find the numbers, and the window manufacturers can’t tell us, we have to assume the worst when doing our Title 24 analysis.

In terms of window manufacturers for our various Title 24 projects, the names we see the most are for Milgard, Loewen (wood or vinyl); Fleetwood, Bonelli, Milgard (metal or metal clad); and Royalite or Velux (skylights) – but there are many more quality makers out there.

Sometimes we don’t see products by name, we just tell the designer what numbers they have to meet or beat. For those who really want metal, Fleetwood has a wide range of styles, including sliding doors, casements, awnings, fixed – as well as energy saving levels.

Here's an example of NFRC ratings for one window manufacturer, Fleetwood. They're one of the few metal frame window products offering triple glazed, argon filled, thermally broken frames.

Ultra High Performing Windows

Most of our Title 24 clients aren’t extremists in this regard, although they all want to get the best window they can within their budgets. The most efficient windows available are typically used either in Passive House certified designs, or in climates with more extreme cold – and sometimes those areas require a different formula with a higher solar heat gain – especially passive solar designs in extreme northern or southern latitudes.

Sorpetaler, Pazen (sold in California through Quantum Builders) or local manufacturer Serious Windows in the South Bay, seem to be the best. And they’re not cheap. The Sorpetaler windows that I saw at Quantum’s offices are as hermetically sealed as an airlock on a spaceship. They’ve got triple glazing, low-e glass, frames with thermal breaks, super low air leakage, argon gas fill – the works. Some of them perform almost as well as a wall in terms of limiting heat loss.

I’ve also heard a few people say that such extremes are wasted in the Bay Area where it’s so temperate that you’re better off investing in other areas rather than windows. Be that as it may, the window’s rated performance does make a huge difference in Title 24 energy compliance – deserved or not.

High-efficiency windows can be executed in a variety of styles as well as custom-built units. Clockwise from left are a modern embedded frame style from Pazen, a double hung unit from Serious Windows, and two traditional examples from Sorpetaler. Pazen and Sorpetaler are German manufacturers, while Serious Windows is located in Mountain View, CA.

NFRC Rating

Well what’s to prevent window manufacturers from making outrageous claims about their products? Regulations and a lot of cumbersome and expensive testing, that’s what. To ensure that people don’t fudge their own test results, window manufacturers are required to send all their stuff to a lab accredited by the National Fenestration Rating Council for physical testing. At the lab, they take the window units and test them, over and over, to measure how much heat they lose, how much of the sun’s heat they let through, and how much air leakage occurs. This process takes up to a year and costs $30,000.

The NFRC rating must be posted on each window unit at the construction site. In addition, California energy code requires that this same rating be etched right onto the glass.

To be considered 100% kosher, these ratings are for the entire manufactured window unit, frame and all. It’s not just the glass. There is something called a “center of glass” measurement that can be used for site-fabricated units such as curtain walls, but officials that we’ve checked with at various local Building Departments have all indicated to us that center-of-glass performance results are not really acceptable for Title 24.

Custom Field Built Windows, Frameless Butt Glazing, and Energy Efficiency

This is a thorny problem because field-built windows don’t have NFRC ratings.

You can forget about single glazed butt joined corner windows, unless they’re small. We recently had a couple of very ambitious glass wall designs, and to our astonishment the one with 67% glass to floor area did OK – eventually – that was because it was all double glazed. Even so, we originally thought it’d need to use triple glazing. Our design client almost had a heart attack. Way too expensive. Eventually we did make it work with double, but they had to make up for it with a lot of HERS tests.

Then we got another design from the same architect that called for miles of single glazed frameless windows including a lot of corner glazing. All single glazed. I thought, “Oh no, we’ll finally have to break our commitment to preserving design intent and tell them we can’t make it work unless they make the windows smaller! But we’ve promised to never, ever do that! They’ll never call us again.” Even there, by counting every possible square inch of interior thermal mass, and pushing them to go to double glazing even for the butt joints, we were able to get it to pass – by 15%, which was a requirement for that particular jurisdiction.

Getting the look of a seamless corner window with double glazing is a challenge, but it's possible. Here's one window detail provided by Swatt|Miers Architects.

Glass Technology

We recently had a question from someone asking what difference the different types of glass such as SolarBan or Cardinal might make. The short version is: refer to the NFRC ratings rather than asking us to evaluate the glass, and bear in mind that some options may cause the glass to appear different. SolarBan 70, which is an option on a lot of Fleetwood window products, offers better performance overall than SolarBan 60 but we had one designer tell us that she didn’t like the look of the 70 – “too shiny”.

For the low-e glass itself, most of the enhanced energy performance is the various coatings on the glass. The good news though is that new products are always coming out with better and more precise performance.

Further Reading

If your thirst for window knowledge still remains unslaked, here’s a good dissertation on windows from the Whole Building Design Guide, a program of the National Institute of Building Sciences.

Everything you think you know about insulation is wrong. That’s in a nutshell what I got from talking with James Morshead of SDI Insulation, Inc. in Burlingame, CA.  SDI is a full-service green insulation contractor offering “sustainable” versions of several common insulation types, including blown-in, spray foam, and fiberglass batts. I wanted to know about high-performing insulation products that would fit into small building cavities, because that’s often something we have to recommend for Title 24 performance modeling. But it’s one thing to say that a project has to fit R38 worth of insulation into a 4-inch roof space, and it’s quite another to find an affordable product that’ll actually do it – and where using that product’s self-reported rating is also acceptable for demonstrating Title 24 compliance.

Summary of the Problem

Insulation is one obvious way to make a home more energy-efficient. Sometimes, existing conditions may limit how much insulation can fit inside the wall, roof, and floor. The catch-22 is when a home needs a higher level of insulation than can easily be fitted inside the existing 2×4 frame walls, and a limited project scope won’t allow that shortfall to be made up elsewhere. In a remodel, retrofitting can be an issue; opening up too many walls could trigger a seismic analysis, and in other cases there may not be the budget to open up new areas.

But what’s the main standard for measuring insulation’s performance? In Title 24, it’s a measure called the R-value which measures the material’s resistance to heat transfer through a 1″ thick piece of that material. According to Morshead, it’s inadequate for the following reasons:

• It’s measured under unrealistically perfect conditions.
• It ignores the need for, and impact of, proper air sealing.
• It ignores the law of diminishing return.

What’s Missing From Insulation R-Values: Air Sealing and Installation Quality

Insulation products are measured in R-value per inch, and they vary widely, with typical fiberglass batt insulation around R 3.5 per inch. Fiberglass batt is the baseline because it’s so commonly used. It’s cheap, flame and pest resistant, and – if installed properly – it does a pretty good job. Two major assumptions that are built into Title 24 are that 1) you can fit up to R15 of fiberglass batts in a typical 2×4 wall, and 2) energy performance increases somewhat proportionally to the amount of insulation. Fiberglass batt insulation has other advantages: easy to install, affordable, fireproof, doesn’t attract moisture, mold, or termites.

But what if you’ve only got a very narrow gap inside the roof of an existing home, and Title 24 says that you need to make the roof R30 or even R38 to do your remodel? Well, one choice could be to go with a different type of insulation product, usually more expensive. But, if you really expect the insulation as actually installed in the home to live up to this expected rating, you will need to consider the factor of air sealing as applied specifically to insulation – and that’s something that’s not adequately addressed in the energy code, or even by insulation vendors themselves.

In many attics, the fiberglass batts are left exposed, without any kind of sealing on the inside. The insulation R value here would be greatly diminished.

This is where spray foam insulation outperforms batt insulation. Spray foam creates an air barrier whereas batt insulation, when left free and open as it is in many typical places like an attic, is as permeable as a mosquito net. “It’s a giant air filter!” said James. “It does absolutely nothing. Your R value could be less than 10% of what it’s supposed to be.”

This installation's a little better. The facing on the front acts as a vapor retardang. Presumably this project would also include a finish such as drywall or board applied flush against the batt insulation on the interior wall. If the builder really intends to prevent air from flowing through the insulation, further air sealing measures would be needed.

According to James, you can use spray foam at a lower R value than batt and still get better performance. [Wow… really?] “You have to bypass regulatory and industry forces that are pushing the R-value as the ultimate measure,” he said. “You have to take the position that you are seeking comfort and efficiency regardless of R-value”.

These two examples show how spray foam can be used to seal air leaks at joists or gaps, either as the main insulating agent or, on the right, in combination with other insulation types such as rigid insulation.

The First Few R-Values Are What Really Matters

The law of diminishing return implies that more is not always better when it comes to insulation. People may think that if R13 is the minimum, then R26 will be twice as good, and so forth with R30, R45, R60. “It’s the first 2 inches of spray foam that matter the most, or the first few increments of batt insulation R-value. There’s a sweet spot where you have enough insulation, and then you should spend additional money elsewhere,” advised James.

With insulation, it's the first few inches that matter the most. For any given climate, there's an optimal level beyond which it's not cost-effective to insulate further.

“At R10 – assuming ideal, airtight conditions – 97.9% of heat transfer is already eliminated,” said James [really??] “so why go to R25?” It’s because of the shortfalls in fiberglass installation techniques. “It’s like they’re saying, ‘Don’t pay attention to the physics, please.’ In reality, it doesn’t make sense to spend all that money chasing that last 10%, the way the Passive House people do. You can better spend your money elsewhere.” I can’t wait to hear the Passive House people screaming at that one.

Surface Temperature Control and R-Value

With insulation, what you are really trying to do is control the temperature of the interior surface of your wall, roof, or floor. James had a good analogy. “Imagine holding a paper cup filled with boiling water, and then imagine the same thing in a styrofoam cup. Which is easier to hold?” The styrofoam cup is a lot easier, obviously. But is R-value alone enough to account for this difference?

James offered a brain teaser for additional illustration. “Imagine a room that is 0 degrees adjacent to another room that’s 80 degrees, and your wall only has room for one inch of R6 insulation. It’s your refrigerator! And yet it obviously does work – why? Because that door stops air movement, which helps with controlling condensation.” Air movement within the building cavity can be exacerbated by a phenomenon called convective looping, as shown below.

One example of convective looping occurs when a warm but uninsulated interior surface heats cold attic air above, causing it to rise and circulate within a joist cavity. This in turn causes cold air to fall towards that warm surface. This example from BuildingScience.com shows actual air leakage from conditioned space into a joist cavity and back.

“R-value measures conducted heat in a bizarre test that is not reality. They take a 2″ thick sample and assume ideal conditions: that there is no air, no moisture, no convective looping – only conducted heat. It’s not the same as a real wall with gaps and air leakage. But we aren’t allowed to use terms like ‘effective’ R-value to distinguish among these conditions.”

(I found some good articles describing this phenomenon more in depth: one on wood pitched roof construction, and one on those ever-exciting floor-kneewall transitions.)

Air Sealing for Different Insulation Types

How you ensure airtightness depends on the type of insulation used.

• Spray foam provides its own air seal. One big advantage of spray foam insulation is that as it expands, it covers holes in the building envelope (such as openings made to accommodate electrical wiring or plumbing) with an air-impermeable barrier. Thus it can also be used prior to installing other insulation, to seal areas around joists, pipes, etc.

• Fiberglass batts must be air sealed on all 6 sides to be effective. “But that almost never happens in reality,” said James. Partly that’s because it’s very difficult to install fiberglass batts correctly, even for builders who’s love to do it perfectly. But here’s a good place to plug another great blog, Energy Vanguard, which has some great articles on just how tricky batt installation can be, including one on hidden air leakage sites in your attic and one on insulation and air infiltration

• With rigid insulation, failure to air seal on the inside can lead to condensation at the roof membrane itself. James responded to one of my questions with, “That’s where some of the horror stories come from. Someone stuck rigid in the roof and filled the cavity, but left it open on the inside so that interior air could flow around the rigid insulation up to the roof, which is cold – then they wonder why they’ve got water.”

• Blown-in insulation reduces air convection currents, and its advantage is, well, you blow it in till you fill the cavity. You don’t have to spend hours cutting and fitting every last piece, or ensuring a flush air barrier on all sides. And, you don’t have to rip the wall open, either.

Moisture

Allowing cold air to accumulate next to a warm but uninsulated surface also invites moisture and condensation to occur. In addition to allowing mold, rot, and deterioration, moisture ruins your thermal performance.

The accumulation of moisture inside a building cavity diminishes the performance of batt and cellulose insulation. Thermal images are a good way to detect water intrusion that's otherwise invisible, as shown in this infrared image of a flat roof. Moisture won't affect the performance of closed-cell spray foam as much, however.

The science of preventing condensation inside cavities varies by climate. The placement and use of air and vapor barriers is beyond the scope of this article, as is the topic of waterproofing (preventing direct water intrusion from the outside). For now we’ll just say that moisture affects some insulation types more than others.

• Cellulose or cotton batt will absorb the water directly, possibly leading to rot, plus the water degrades the insulation’s thermal performance.

• Fiberglass batt can absorb water even if the fibers themselves don’t swell, and the weight of built-up moisture can cause the instulation to sag, accumulate mold, or experience degraded thermal performance.

• Closed cell spray foams are vapor retarders and moisture resistant, although if water condenses inside the cavity somehow, it might affect adhesion.

• Open cell spray foam can absorb water from condensation in the air.

Ice Damming and Spray Foam

Snow melt is a special case that is less urgent in most of California, but I’ll mention it anyway. I was asking about some of the horror stories about spray foam and mold. James quickly leaped to the defense of spray foam. “It’s not the product, it’s the construction. Some of those horror stories involve insufficient R value or poor installation in snow load areas. R38 is OK for insulation against cold air alone, but in snow country you need R50 to keep the roof surface cool enough to prevent the snow on it from melting. The surface temperature of roof must stay below freezing to prevent ice damming. So, you can either ventilate the heck out of the roof, or you can use enough spray foam and ventilate the upper roof assembly instead.”

In snow areas, care should be taken to avoid "hot spots" on the roof that can cause snow to melt, re-freeze, and seep back into the house.

Ventilated vs Unventilated Roof Assemblies

James mentioned the possibility of an unventilated roof assembly with closed-cell spray foam. “You can do more cool architectural tricks with them.”

However, attics with ventilation are far more common, and James had a lot to say about them. “Conventional vented attics are energy sucks. A vented attic leaks heat both from the vents, and from insulation not being closed on all 6 sides. How many attics have you seen with the batts just exposed? All the summer heat goes into the attic, and while venting lets the hot air out, it does nothing about the radiant heat coming in. That radiant heat still transfers even with vents present, and that’s why so many attics are 130 degrees in the summer.”

“And all that vented air is moving over the open fiberglass. People say ‘I can’t get my house to cool off at night’ because the roof is still hot and it’s radiating heat into the interior.” Radiant heat actually radiates directly from the hot interior surface, even if the air itself is cold. “Radiant heat transfer is powerful force.”

“But if you move the building’s thermal envelope to the roof deck, with rigid foam or spray foam at the roof line, the interior surface temperature of the attic will be the same as the house.”

Moving the building's thermal envelope from the attic ceiling to the roof line helps keep the attic cooler.

Radiant Barriers and Cool Roofs

While not strictly “insulation”, radiant barriers also act to resist the transfer of heat from the roof into the home – specifically, solar heat gain. There are plenty of do’s and don’ts for these, starting with whether it’s even appropriate for your climate zone or not. James had a few suggestions: “Don’t put spray foam over a radiant barrier, because it won’t be able do its job. It needs an air space and a temperature difference. ”

James also noted that cool roofs can get so cold at night that they attract condensation, even during construction. But this should probably be a separate article.

Types of Insulation

James and I didn’t go through every possible type of insulation, but we did discuss some pros and cons of the main types. I’d refer readers to the Wikipedia article, which has a more exhaustive discussion of different types of insulation, their performance, and general pros and cons.

Fiberglass batt

Pros: common and cheap; doesn’t degrade; fire resistant; not a food source for pests or mold
Cons: If it’s not well sealed, dust and moisture can collect on it and then mold can grow.

“Fiberglass batt must be in contact with an air barrier on all 6 sides. It won’t perform if it has even one side exposed – too air permeable. If it’s not sealed, it’s just a giant air filter. To make fiberglass perform closer to its rated R-value is more labor-intensive. You need to do a very careful installation, and air seal it properly.”

Fiberglass batt insulation is one of the most commonly used insulation types, especially for homes.

Blown-in fiberglass or cellulose

Pros: Fills every crack. Denser, which restricts air movement. Provides an acoustic barrier. Simpler installation. Doesn’t require full opening of the building cavity. Non-toxic.
Cons: Not a full air seal; can be heavy on ceilings; can absorb moisture; settles over time.

“It’s OK for walls or attics, not so much for frame floors or roofs. It’s easy to install – for an open wall, you put a fabric blanket up on the wall and blow it in.”

Blown-in insulation can be a good choice for filling building cavities quickly and cheaply. Left: blown-in fiberglass insulation. Right: blown-in cellulose insulation.

Cotton batt

Pro: Its green appeal, being a recycled natural fiber. Fibers are non-irritating, unlike fiberglass.
Cons: Expensive; difficult to cut and fit. Moisture could be a problem if it gets into the wall. Not a complete air seal.

“They don’t come in standard sizes to fit a 15.5″ cavity. It’s 16″ wide and you have to cut it every single time. The manufacturers haven’t learned to size it for conventional building methods yet, and so it’s very labor-intensive to install. It’s a cool idea, and it feels green, but is it?”

Cotton batt insulation, or "blue jean insulation" is recycled and natural.

Spray foam
Comes in two types: closed cell and open cell. Difference is density. They both come with a liquid medium and an expander gas, which can vary as to what it is. Open cell is cheaper and not quite as insulating.

Pros: Airtight seal; closed cell is a vapor retarder and air flow retarder as well. Relatively high R value for the size.
Cons: Expensive; needs an experienced installer; requires fire rated barrier; toxic during installation; may emit toxic gases during a fire; keep away from direct sunlight and solvents.

Spray foam insulation creates an air seal. Shown here is low-density spray foam.

Rigid insulation

Pros: Same high thermal performance as spray foam. Can use on exterior wall, roof, or under-slab to control thermal bridging. Good for high R values in small spaces. Water resistant; can be used for foundation and under-slab insulation.
Cons: Requires air sealing to prevent air movement through the cracks; requires skilled installation and construction techniques to use; expensive; keep away from sunlight and solvents; may emit toxic fumes in a fire;

“Construction techniques are harder. Different jamb sizes and flashing. More cutting and fitting required. It’s harder to put in wiring afterwards, because you have to cut into the board.”

The term "rigid insulation" covers a wide spectrum of products. Left: sandwich of wood fiber and polystyrene. Center: phenolic foam board with foil backing. Right: Application of rigid foam panels as foundation insulation.

Best Bang for the Buck

After going on at such length about the virtues of spray foam, James did have a few good words for fiberglass batts, too. “You can achieve almost the same level of comfort with batt if you do it right, and youdon’t leave gaps or air leakage to create drafts. The surface temperature of the wall on both sides is important too. If a wall is cold, the home is less comfortable – not only because of lowered air temperature, but because of radiant heat loss as well.”

How “Green” are the Foams?

I asked James a few general “green” questions, since many of our Title 24 clients are interested in the larger issues as well as measurable energy performance. So how “green” is each type of insulation? Aside from the fact that using insulation at all is better than wasting energy, the “green” question could be addressed by looking at a number of factors:

• Whether off-gassing will somehow affect indoor air quality for the occupants

• Toxicity during a fire, even for materials that are themselves flame-retardant

• Global warming, could be result of ozone-depleting gases either during manufacture or after installation

• Energy used in the manufacture and transport of the materials, both amount of energy used, and whether it comes from fossil fuels
• Whether the insulation products themselves are made from petroleum by-products

• How much energy is saved over the lifetime of the building

Aside from cost and efficiency, some of our clients have voiced other concerns, especially with toxicity. It’s ironic that being “green” and reducing energy use might involve the use of toxic materials, but that’s one thing that could happen. Fortunately, it’s not inevitable, although some care should be taken when selecting individual products within a category.

How Green is Blown-In Cellulose?

Cellulose is “kind of green”, according to James, having a high recycled content. It does have some plastics, and printed paper with “unknown inks” although it seems farfetched that the ink on recycled cellulose insulation would have much of an effect on indoor air quality. Fire toxicity, maybe… but building a fireproof home is a different goal than making an energy-efficient one, and at some point you have to make choices about priorities.

Are Spray Foams Toxic?

James didn’t think that even the spray foams were toxic to people. “Not many products are toxic for indoor air quality,” he said. “A lot of that perception is just the industry players fighting each other – fiberglass vs. cellulose vs. foam – and promoting disinformation about the other products. The real test of whether something is sustainable is to ask ‘What will my grandkids think about what I’m doing now?’ What’s the impact on the environment, on the grid, and on quality of life?”

(The Wikipedia article on building insulation materials doesn’t completely back him up on this. First off, they contain petrochemicals. Second, they have to be correctly mixed in the field in order to “cure” correctly, and the installers must wear protective breathing apparatus. Third, some of the agents used, while not harmful to the ozone layer, are greenhouse gases. However, despite some reports of chemically sensitive people having a bad reaction to it, spray foam is still the insulation of choice for many green builders, and can be used in combination with other insulation products especially for air sealing.)

Both spray foam and rigid insulation can be made from a huge variety of substances, even soy, although even the supposed soy-based ones are still mainly petrochemical. Not being a chemist myself, I can’t discuss the issues particular to each: isocyanurate, isocyanate, polyurethane, polyicynene, cementitious foam, polystyrene, CFCs, HFCs, HCFCs. As with many other areas, one recommendation is to select a good builder who is familiar with installing the type of insulation desired – and in your climate area. Chemically sensitive people may want to evaluate samples prior to applying it all over their home, since it seems like some of the worst experiences are from do-it-yourself types or from improper installation.

Improper installation can also include poorly designed wall assemblies that permit moisture buildup. This can lead to toxic conditions if mold occurs, apart from any toxicity in the materials themselves.

Forget About Certifications – Just Save Energy!

It’s really the energy reduction as applied to many homes, not just one or two showcase LEED places, that will have the greatest impact on Spaceship Earth, asserted James. “LEED, Passive Houses, and Net Zero are playthings of the rich,” he opined. “If multiple homeowners spent a fraction of that on their own homes it’d do a whole lot more than one or two ultra-efficient showcase homes that no one else could afford to build. Even for the average home, a 30% reduction in energy use is achievable almost with your eyes closed. And, that 30% savings requires some mental energy in terms of good integration of systems and good choices.”

I pressed him about the Net Zero remark, and it’s the obsession with certification that he thinks is overkill. “Anyone can follow the Net Zero method and improve their home, or build using Passive House techniques. It’s not always worthwhile getting that last 10% of the way there for full certification.” I said that having a zero energy bill for the year was not a “plaything of the rich”, and James responded with, “My clients care more about budget and comfort than about what awards they’ll get.”

He also said, “These showcase homes are like concept cars. Maybe in another generation they’ll be the standard, but for now, it’s better to concentrate on the average home than on a few visionary early adopters.” While I agree that energy efficiency should be accessible to the Teeming Millions, I also think that early adopters are extremely important, because their homes are more than concepts – they’re long-term experiments that will ultimately prove (or not) the proposed concepts. And so what if they don’t work? That’s part of the risk of the experimenter, is to learn the right lessons from failure so the next attempt works better.

Since he spent lot of time bending my ear about the deficiencies in Title 24 itself asked James what he thought should be in the prescriptive performance standards. He responded, “Airtight construction, correctly installed insulation, and correctly sized HVAC systems. An average house should have all this without special consultants or green certification.”

Antiquated Standards

"California's Title 24 energy code is like using a whip and buggy to measure jet-engine technologies," says James Morshead, Senior Project Manager and Building Science Director at SDI Insulation.

“The current rating system for insulation is completely antiquated,” said James. Well, as a vendor, he’d probably want to make that point regarding his competitors. In fact, he did say “There’s a lot of disinformation out there, and much of it is due to industry competition. The fiberglass guys try to dismiss the spray-foam guys and vice versa.”

James wasn’t shy about critiquing Title 24 as a standard, either. “What ends up in the code can be largely political,” he said. “That’s why the Title 24 Quality of Insulation Installation credit recognizes closed cell spray foam insulation, but not open cell foam – at least, not yet.” (The QII test evaluates the quality of batt insulation installation, and it must be performed by a HERS inspector.) He went even farther than that by saying, “Title 24 can often a hindrance in highly innovative building envelope designs, because it focuses on numbers on paper without consideration for what actually works, or for cost. However, it does encourage overall improvements in the majority of typical projects, which is its intended purpose.” He’s right about the lag time. The code can’t keep pace with new developments, and often a newly invented measure that offers superior performance in the real world won’t always comply with what’s already in the code. It simply takes time for codes to be re-evaluated and updated to account for these new technologies. In those cases, it’s often up to the local building officials. “But they also have less leeway than they used to,” said James.

A few months ago, we interviewed Bronwyn Barry of Quantum Builders on the Passive House standard. When I called her again to ask about ventilation, she recommended Zehnder, a Swiss company, because their products are Passive House certified and if there’s anyone who knows about ventilation, it’s the Passive House folks. Passive Houses need state-of-the-art ventilation because they rely so heavily on an airtight building envelope, and their stringent energy budgets also mandate the most energy-efficient motors available.

I spoke with Barry Stephens of Zehnder America, the U.S. subsidiary. Zehnder has over 100 projects all over the U.S., including some larger residential complexes. Two-thirds of their projects are Passive House projects, but the company also works with other types of energy retrofits. You can see a great animation of their system here. Barry then referred me to his brother Charlie Stephens of the Northwest Energy Efficiency Alliance, who’s an energy research expert.

We asked both of them some general questions about ventilation principles, along with specific questions for Barry about the Zehnder product line. Most of the discussions here reference the Passive House standard, because it’s so far ahead on ventilation. In fact, if you’re looking for a good ventilation consultant, finding someone with Passive House certification wouldn’t be a bad place to start.

WHY does a home need a ventilation system?

In other words, why is “just opening a window” or “just running the bathroom fan” not enough?

There’s a definite knowledge gap in the residential design and build communities about the need for mechanical ventilation systems. The newest version of California’s energy code mandates whole-house ventilation for new construction based on ASHRAE Standard 62.2, “Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings”. This standard includes some specifics on output, such as the number of cubic feet per minute of air moved. However, Title 24 gives little direction on ventilation system design, installation, or operation. The old theory was that a simple exhaust fan in the bathroom would create negative pressure inside the home which would, in turn, draw fresh air in directly through the walls of the home. In older times, homes were more air-permeable (i.e., drafty) and this was a simple, low-tech solution. Today, however, it’s no longer enough.

Old-school ventilation methods from left to right: bathroom exhaust fan, opening a window, and kitchen range hoods. For today's energy-efficient, airtight homes, these are not enough.

The main reason to ventilate include comfort and health – prevent stale air from building up, and also avoid bringing in outside pollutants such as dust, mold, or pollen. But why the sudden focus on ventilation? Several reasons, among them the following:

• Homes are far more airtight nowadays, leading to a new emphasis on the need for indoor air quality.

• Poor circulation within a home means fresh air doesn’t get to where it’s most needed, like bedrooms. If you’re relying solely on exhaust vented from a bathroom, what happens when doors are closed?

• Exhaust-only ventilation causes pressure imbalance inside the home, not always desirable.

• Air coming in through any old crack in the house means you’re not controlling the source very well. You could be bringing in all sorts of pollutants and dust. Better to choose your intake points and add filtering.

Leaving a window open in a major urban area could be the WORST thing for your indoor air quality, not to mention your peace of mind.

• Drawing air in through the walls introduces the risk of moisture condensation inside the walls, especially if there’s a big temperature differential between outside and inside air.

• Ventilation systems now include heat recovery ventilation units (HRV) so that you’re not continually bringing cold air into the house and then using extra energy to heat it. Instead, heat from the inside air that’s being exhausted outward is transferred directly to the intake air. Essentially, you’re recycling your own heat without sacrificing your fresh air supply.

Thermal imaging shows areas of cold air infiltration. If you're relying on an exhaust fan to draw air through the home for ventilation even in the wintertime, do you really want all this cold air to add to your heating bills?

• Additional features can remove humidity from intake air in climates where that is a concern. One thing to note is that humid air takes more energy to heat or cool than dry air, so managing humidity can save energy, up to 15% on heating in cold climates and up to 45% on cooling in hot, humid climates.

Carbon dioxide buildup creates stuffy rooms and foggy brains

One problem with a poorly ventilated, airtight building is carbon dioxide buildup – stale air. Too much CO2 in the air can cause people to feel sleepy, or worse. This problem doesn’t get as much attention as carbon monoxide poisoning, but it’s still a concern. Carbon dioxide is, of course, a naturally occurring by-product of human respiration. Carbon dioxide levels in fresh air measured in parts per million varies between 0.036% (360 ppm) and 0.039% (390 ppm). It can go higher indoors, perhaps 600-800ppm. Some literature implies that a stuffy auditorium could go as high as 10,000 ppm, which is high enough to cause noticeable drowsiness.

A recent study presented at a Passive House conference showed that carbon dioxide levels in a modern, airtight home could actually accumulate high enough - especially during the night - to make people wake up feeling tired the next morning.

The length of exposure is a factor as well. Barry Stephens mentioned a study he saw presented at a Passive House conference at Brandeis University showing carbon dioxide levels throughout the night inside the bedroom of a modern, airtight home as measured in parts per million. In some of these homes, the CO2 level would rise to 3,000 or even 4,000 PPM by morning, causing occupants to wake up feeling tired.

OSHA’s safety threshold for CO2 level is 5,000 PPM (0.5%) over 8 hours of exposure. At levels over 10,000 or 20,000 ppm more serious symptoms of carbon dioxide poisoning start to appear: headache, lethargy, mental fogginess, confusion, irregular heartbeat, anxiety. Carbon dioxide levels of 100,000 ppm can cause loss of consciousness or even death.

“The correlation between CO2 levels in buildings and health systems in living organisms isn’t well established at this point,” cautioned Charlie Stephens. “[But] it’s the reason why many people have noticed that they sleep better with a window open.”

How do you know if you need a fully pressure-balanced whole-house ventilation system?

Is there some sort of test or threshold for determining whether a home needs the full ventilation treatment? Not yet. A house that passes the California blower door test could potentially benefit from whole-house ventilation. If it is extremely airtight, enough to have under 0.6 air changes per hour (that’s the Passive House standard) it should definitely have one. This still leaves a large gray area of uncertainty.

A pressure balanced ventilation system includes specific controls for both air intake and air exhaust.

Building and energy codes are mandating tighter buildings, increasing the importance of ventilation. Building air infiltration, i.e., air leakage, is usually measured using a blower door test and is often expressed in terms of number of air changes per hour (ACH). So how many ACH does it take to change a ventilation requirement? Well… the U.S. Department of Energy is proposing 5 ACH as the threshold for requiring mechanical ventilation, but since an “average” new home might now be 3 ACH and an “efficient” home might be around 1.5 ACH, all we can say is it’s somewhere in that range.

“There is no defined ACH level that I know of at which ventilation is mandated, or even recommended at this point, because it hasn’t been much of an issue until recently,” said Charlie. “What they would be saying is that for any ACH level below this number, you would be required to have an effective ventilation system, but almost no one knows what an ‘effective’ ventilation system is, except in the case of a properly designed and installed HRV or ERV system.”

And what does ACH measure, anyway?

Air changes per hour is one way to measure the permeability of a building envelope, based on the known physical behavior of gases such as our own air and atmosphere. As we know, gases expand to fill all available space, and this expansiveness creates pressure – air pressure. The more space it has to expand within, the lower the air’s pressure becomes. If there are different air pressures inside vs. outside, air will automatically begin to seep from the higher pressure enclosure into the lower pressure surrounding areas. The higher this differential, the faster the seepage. “The measurements for ACH levels of air leakage are taken at a differential pressure of 50 pascals (0.2 inches water gauge) between the indoors and outdoors,” explained Charlie.

(The measure’s full name is ACH50 – we’re abbreviating.)

Who knew that there were so many ways for air to get in or out of a house?

So what ACH level would be considered “normal”?

Charlie stressed that the proposed 2012 IECC Residential Energy Code upgrades include a provision for a maximum ACH level of 3.0. (Title 24 uses a different calculation, not ACH, and the building must fall within a range and not be TOO tight.) But what is “normal” for ACH as of today? Here are a few random statisics from Northouse and Green Building Advisor:

• An average home’s ACH is 3-3.5 in Alberta and 3.9 in Wisconsin
• The average for new construction in Minnesota is 2.5 ACH
• Older homes might be around 4-9 ACH
• An “efficient” home is around 1.5 ACH

Energy researchers all over the country are wrestling with this question even as we speak, including the Northwest Energy Efficiency Alliance in Portland, OR – Charlie Stephen’s group. “The NEEA ventilation field research will be conducted on recently built homes of recent and reasonably airtight construction during 2011 and 2012,” Charlie informed me. “The monitoring of CO2 levels isn’t so much an end as it is a means to understand how air is moving in a home. It’s essentially a cheap tracer gas.” Even though it’s not the primary purpose of the study, it may help to begin associating CO2 levels with specific ACH numbers.

“We’re also measuring the performance of the mechanical ventilation components (such as fans) installed in the homes, and trying to understand how they’re operated, and whether or not they are effective at providing sufficient ventilation air for the occupants of the home. We’re only looking at homes we consider to be quite airtight – probably 3.0 ACH or lower. We don’t know how many of those we’ll find in our sample set, which is a 4-state sample of existing homes. We’re only looking at 30-50 homes initially. We may look at more after the first phase of the research, depending on what we find. As you suggest, all of our sample homes will have to be blower door-tested to start with.”

But you don’t really know the ACH until you do a blower door test, and you can’t do this until the house is already built.

We have been encouraging our Title 24 clients to plan ahead in the early design stages for things like systems, but how can you plan ahead for something that’s got to be measured in the field after being built? Charlie had an answer, although it still involves measurements taken during construction.

“Blower door tests can be conducted before the home is finished, but not before the air barrier is fully in place. This tends to be after sheetrock, but before interior finish, if the home is new. Many of the sites of air leakage can be accessed from inside the house  in the crawlspace, basement, or attic, and so some corrections are possible even in remodels. But it’s a lot easier in new homes to pay attention to the air barrier for the envelope and to be meticulous about air-sealing as the home is built. Lots of homes are achieving air leakage results under 1.0 ACH50, so it’s not impossible, or even difficult in many cases.”

Do HRV systems make sense in warmer climates, too?

Heat Recovery Ventilation systems make sense in cold climates, but what about hot climates? Actually yes, although in places like Florida you might want an Energy Recovery Ventilation system instead. An ERV will remove some of the humidity from the intake air. Why bother with that? Because it takes more energy to change the temperature of humid air than it does to condition dry air. (It takes more energy to change water temperature than air, and the presence of water in the air changes the air’s thermodynamic properties.)

The difference between the mechanical units is that an ERV uses a membrane that transfers both moisture and heat, while an HRV transfers heat through layers of plastic sheets. As to where exactly to change from one to the other, that’s still up in the air. But you can if you want to; Zehnder units have swappable cores to change from HRV to ERV.

How does the Zehnder ventilation system work in a retrofit?

The Zehnder ventilation system uses smaller, flexible ducts that can be fed through the walls, rather than large metal ducting that requires extensive use of sealing and mastic. Half of Zehnder’s projects are retrofits, usually including other energy features besides heat-recovery ventilation.

One project Barry mentioned was a homeowner named Tad Everhart in Portland. He’s now a Passive House consultant. He did a full Passive House retrofit on his 2,100 SF home. For a Passive House, you need a fully sealed ventilation system with heat recovery, that meets stringent requirements for both energy efficiency and air movement. As Barry Stephens tells it, Everhart was intrigued by Zehnder’s ducting system, and found that he could feed it through the walls just by cutting a small hole. He did the downstairs first using 2 6-tube manifolds, and later did the upstairs the same.

Tad Everhart, a homeowner in Portland, OR, did a full Passive House retrofit on his existing home which also included installing a pressure-balanced, whole-house ventilation system with heat recovery.

Another set of projects that Barry mentioned include a series of gut rehabs of Brooklyn brownstones, where the owners are retrofitting to the Passive House standard. There’s a whole core of Passive House consultants, mainly architects, in the New York area, including Ken Levenson, Jeremy Shannon of Prospect Architecture, and David White of Right Environments. Their work includes both new designs and retrofits.

Tell me more about deep energy retrofits.

“A lot of people start by thinking about the envelope,” said Barry. “They seal it up tight and add insulation, upgrade the windows, maybe re-do their ductwork and heating system. Then they do a blower door test and say, ‘Oh yeah… I guess we have to add ventilation.’”

Barry noted another thing about deep energy retrofits. When you tighten and insulate a building, the heating and cooling loads go way down. In a recent interview, Green Builder Jeff King told us that many HVAC systems are already grossly oversized to begin with. After a retrofit, those systems are REALLY oversized.

You wouldn't need a factory-sized furnace for a tiny cabin, but that's what most home HVAC systems are, essentially - grossly oversized. A furnace that's too big will cycle on and off too frequently, leading to temperature fluctuations rather than maintaining an even, constant temperature.

Can you integrate whole-house heat recovery ventilation with a conventional forced air heating system?

Yes, you can integrate HRV into existing forced-air systems. The existing forced-air heating system does not make whole-house HRV redundant, because the forced-air heating system by itself is just moving air around inside the home, unless you add an extra intake by the furnace to add fresh air. To add a heat-recovery ventilation system in a building with existing forced-air heating, you can install the HRV intake to feed into the furnace return plenum on one end, and to draw exhaust out on the other. This would reduce load on the furnace because it’s no longer having to heat outside air directly. If it’s 20 degrees outside and you add the HRV, then the furnace no longer has to heat up 20-degree air. Instead, it’s getting air that’s already around 65 degrees.

Charlie explained the concept of a hybrid ventilation system that is integrated with an existing forced-air heating system. In this scenario, fresh air would be supplied just before the air handler, in the return duct, while exhaust is through typical bathroom fans. Since this would potentially lead to a pressure imbalance, an additional step is needed. “To create a balanced ventilation system, you’d measure pressure inside the house relative to outdoors, and adjust the capacity of the exhaust fan(s) to match the supply air intake rate at the air handler return. Obviously, the fans would have to be controlled to operate at the same time. And most exhaust fans and air handlers do not have adjustable capacity, so controlling flow is done with dampers – not a particularly efficient way to manage air flow.”

What is the cost of a Zehnder ventilation system, including design, equipment, installation?

For a Zehnder ventilation system, an average 2,500 SF house with heat-recovery, ducting, silencers (a noise abatement option), controls, and installation service would be $6,500 – $7,500. The equipment is around $5,500 and installation another $2,000. Installation takes half the time compared with conventional metal ducting, because it’s smaller, and the connections are simple O-rings and clips rather than requiring extensive use of mastic, sealing, etc. It’s a lot lighter too – one person can carry all the tubing. Barry estimates a typical house project would take 2 people and 2 days.

Note, however, that HVAC subcontractors have bid higher, sometimes $6,000 because they’re unfamiliar with the new technology and that’s how long it might take for them to install a more conventional HVAC system. Barry suggested that you might have to bypass the HVAC guys altogether, or push back to get them down to a more reasonable installation figure.

Can a regular builder or HVAC contractor install a Zehnder ventilation system?

The system isn’t hard to install, in fact it’s lighter and takes less time to install than a conventional forced-air heating system with metal ductwork. Zehnder has been providing the system specifications and design for projects, so all the builder has to do is follow the instructions for installation and commissioning. Builders don’t need to be Zehnder-certified. However, because conventional HVAC contractors have been over-bidding on installation, Barry notes that on many projects it’s the carpenters who’ve been installing the ventilation and ducting, and it’s working fine.

The installers don’t have to design or spec the system. Zehnder has been doing that – taking the plans, doing the layout and specifying the equipment needed.

What does the architect have to do during the design phase to account for a whole-house ventilation system?

Barry/Zehnder: Architects need to plan for the chases. “We can’t just let the HVAC guys figure it out afterwards,” said Barry. Zehnder’s ducts are 3 inches in diameter. For example, consider 5 supplies and 5 returns with 3″ ducts, plus a main intake and a main exhaust going to the outside, each around 6 or 7 inches. You can put the HRV unit in the basement, but don’t forget to plan for chases going to other floors. For example, consider fitting them into stairwells or the back of a closet.

Installation of a Zehnder HRV system in Portland, OR. The components fit within the framing. Photo: Charlie Stephens, Northwest Energy Efficiency Alliance

Barry/Zehnder: One important point is to locate the HRV unit close to an outside wall, to minimize duct length between the air intake and the HRV unit. The 6″ intake duct is surface area that’s exposed to the outside, and although it’s protected, it’s not as well insulated as a solid wall would be. The Passive House standard actually penalizes you for long intake and exhaust runs because they waste energy.

Barry noted a few “gotchas” with new structural systems were noted, particularly laminated veneer lumber beams. You can’t drill through them or thread through them the way you can with a regular truss. This issue comes up sometimes with other structural systems as well, with some materials requiring pre-drilling or fabrication because they can’t be easily modified on site to accommodate last-minute decisions.

These examples of cover grids for room vents are from the Zehnder site. From left to right: floor outlets, wall outlets, ceiling outlets

Does every room need its own intake and exhaust?

No. You can have intake in some rooms and exhaust from others. Barry’s strategy is as follows: get fresh air IN to the bedrooms and living spaces, and get exhaust OUT of bathrooms and kitchens. You want to have constant low-level air movement. This distributes the air quickly and evenly throughout the home.

This diagram from Zehnder America shows one sample schematic of a centralized whole-house ventilation system with pressure balancing and heat recovery. Here, fresh air (blue) is piped in to living spaces and bedrooms while other vents draw out stale air (red) from the bathroom and kitchen.

I’m guessing that the exhaust from the bathroom doesn’t go straight out the window.

The bathroom’s exhaust air doesn’t go straight out the window as with an exhaust fan, but instead that it is drawn back through the central HRV unit, where its heat energy is removed. Only then is the air expelled from the home.

Charlie: All of the air being exhausted by the HRV or ERV leaves the house through the main unit’s HRV or ERV ducting, but almost all of the energy in the air being exhausted is transferred back into the incoming air stream. Thus, the fresh air from the supply intake is only a couple of degrees Fahrenheit different in temperature than the indoor air being exhausted, regardless of the temperature outside. Unlike a conventional heating/cooling system, the air won’t be returning to be recycled inside the home. Instead, it’s being sent outside – exhausted, along with all of the moisture, odors and contaminants in the air.

Is it important to have ducts placed high or low on the wall?

Barry/Zehnder: Where we use register boxes, the supply tends to be low and the return is high. Diffusers can be either.

This diagram from Zehnder America shows how the chases are integrated into a floor.

What’s the maximum recommended duct length for a Zehnder ventilation system?

“I’d say 50 feet, but the number of bends is actually a lot more important. You want to minimize bends. You might be OK with a straight duct that’s as long as 100 feet, but if it’s got several 90-degree bends, the max length might be more like 20 feet,” said Barry.

Minimizing bends and angles in conventional ducting system design is important, because it minimizes air turbulence and maximizes air flow. Left: a very bad example of duct design. Right: this duct design (from another company) includes a fan to assist in moving air around the bends.

How many Zehnder HRV units would you need for a single home?

For Zehnder products in a typical single-family residence, usually just one. It’s based on the total conditioned air volume inside the home, the desired amount of air changes per hour, and the number of people. Sometimes even family pets get counted. Here’s a little known fact – did you know that cats and dogs use more oxygen for their body weight than people? It’s because they breathe faster. If you have a bedroom with two people and two large dogs all sleeping in there, it’s going to collect a lot more CO2.

A heat-recovery ventilation unit from Zehnder. Intake is on one side, exhaust on the other; the heat energy from the exhaust side is transferred to new intake air without actually mixing the air streams.

Can you retrofit a Zehnder ventilation system in a single apartment?

Yes. You can get a smaller unit installed on the wall with vents to the outside. A lot of apartments in Europe are doing this. For an apartment, you don’t need chases in every room, maybe just the main room and the bathroom.

What about maintenance and troubleshooting?

For Zehnder systems, the filters should be changed once a year, and they are externally accessible so the homeowners can do it themselves. Some filters can actually be rinsed with water and reused, but still should be replaced annually. For the HRV unit, you can wash the core with water – you need only a screwdriver to take it off. Ducts can be cleaned, either with a special “roto” type brush or a vacuum. The ducts are smooth with no connectors so it’s easy to brush them out.

Zehnder ventilation system maintenance. Left: removing an air filter. Right: removing the heat exchanger, which can be cleaned with water.

What are the options for filtering?

Zehnder products fall into two main levels, measured using the Minimum Efficiency Reporting Value system, or MERV.  MERV ratings are based on the size of the molecules that are filtered out. The higher the rating, the smaller the molecules that filter can catch. Zehnder filter options are twofold:

• The G4, which is MERV 7-8 – fine for eliminating pollen.
• The F7, which is MERV 13 – best residential dust control; almost good enough for an industrial “clean room”

What about filtering for smog?

Zehnder’s post-filtering solutions include an optional filter box that can go up to MERV 15 and includes charcoal filters. Charcoal is what you want for smog gases such as carbon monoxide or industrial fumes. This box is big, to keep air flowing freely. The filter box is 15-24″ long x 8″ x 10″. Costs $400. Barry noted that filtering outside air won’t necessarily help with dust mites or mold, because those air contaminants are already IN the house. What the filters do is remove outside particulates like pollen, street dust, or soot.

A well-designed home ventilation system can filter out particles that exist in outdoor air, such as diesel soot or pollen. It won't, however, remove contaminants that originate indoors: household dust and such.

Do you recommend installing CO2 sensors too?

Barry/Zehnder: We offer sensors for CO2 levels and relative humidity. They can be tied to our controls so the system automatically adjusts. A karate studio, for example, might have a sensor so that when there are only 2 people in the studio, the system can stay on low – but if there are 25 people working out hard and raising the CO2 level, the sensor automatically kicks the system up to a higher level.

A CO2 monitor like this one shows the concentration of carbon dioxide in the air. Outside air might be 360 parts per million.

All the Zehnder units have a summer bypass feature, too. In the summer, it might be hot in the day but cooler at night. So at night you might want to bypass the HRV to help keep the house cooler. Charlie adds, “the ‘summer bypass’ feature is an automatic one – you push the button to engage the feature, then the HRV decides when to bypass the heat recovery core.”

Does Zehnder provide a commissioning protocol for use by installers?

There is a document on how to test whether the system is properly installed and functioning. Barry recommends using an energy auditor for this, someone who’s got flow hoods, and to have them test room by room for airflow and pressure balance. They can then adjust the air flow at various registers, using what Charlie described as “an ingenious bundle of tubes and washers”.

A Doubting Thomas Chimes In…

Many experienced residential architects will be questioning the utility of requiring yet another system to be incorporated into their home designs. Here we’re posing some questions from the skeptic’s gallery. Readers will have to make up their own minds – we hope we’ve given them enough food for thought, and maybe a few yardsticks, too. The designation of something like “stale air” is pretty vague, but we’ve all been in rooms that were far too stuffy – and if you had the choice, and you’re already spending the money to customize a home, wouldn’t you prefer to be breathing clean air instead?

What about having a bathroom fan with ceiling fans in every room? Won’t that move enough air around?

You’re still dealing with a pressure imbalance, uncontrolled air intake, and if doors between rooms are closed, you’ll still have pockets of stale air in the bedrooms at night – the last place you want it. In homes with radiant heating systems, there isn’t even the air circulation within the home that you would get from a conventional forced-air heating system.

Charlie adds, “in a very airtight house, with all of the windows and doors closed, there’s no guarantee of how much air will come in when the exhaust fan is on, and air that didn’t come in can’t be exhausted out. We suspect that exhaust fan flows in tight houses may be much lower than the fan’s rated capacity, and so total ventilation may be much lower than people think. That’s one reason why we’re doing the field research.”

But that’s ridiculous. I’ve been building efficient homes for 20 years and I think whole-house ventilation adds needless cost.

It does add somewhat to the cost, but it’s still something to consider if you’re already doing a renovation. There’s an opportunity to add in the chases while the walls and floors are already open.

Charlie adds, “People who have been building ‘efficient homes’ for years have almost never been building airtight efficient homes -until recently. Any home that leaks air at more than about 5 ACH is probably leaky enough to keep the builder and the occupants out of serious trouble regarding CO2 buildup, but that doesn’t mean the indoor environment isn’t laden with other contaminants or excessive moisture – and CO2 at times. A properly designed and installed balanced heat recovery ventilation system solves multiple problems and delivers multiple benefits in any home that is substantially airtight.”

OK, so mold is a problem in Florida. Would a house that passes a blower door test but relied only on a bathroom exhaust fan for ventilation still be at risk for mold in a drier climate like California? Why can’t we just use vapor barriers to manage this?

Charlie explained why vapor barriers aren’t enough to manage mold. Mold can exist wherever it can find three things: food, cool temperatures, and high relative humidity or bulk moisture. In a lightly or poorly insulated home, or one where there are thermal bypasses in the insulation system (e.g. where framing members pass all the way from the interior to the exterior), mold can grow on damp surfaces with a food supply such as cellulose.

“An HRV in this circumstance removes excess moisture from the home. When fresh air comes in, its temperature is elevated in the heat recovery core to within a couple of degrees Fahrenheit of the indoor temperature, which significantly lowers its relative humidity, helping to maintain a lower relative humidity level in the home, in spite of elevated levels of cooking or showering activity. There are lots of climate zones in California where mold is an issue. And if indoor relative humidity levels are consistently elevated, for whatever reason, mold can even be a problem in the desert.”

Yes, I know… opening a window is not enough to ventilate every home, but at least I didn't end this article with a whole-house mold photo.

We all know that every home in California’s going to be Net Zero by 2030, right? Actually, it’s every NEW home built after 2030 – the old homes can go on being inefficient, until the next time someone needs a building permit. At that point, serious attention may need to be paid to bringing the home up to date. And, increased enforcement now occurs at many different points throughout the project, making it harder to do swaps during construction.

The truth is, architects can’t rely on the builder anymore to specify and install systems and materials as an afterthought, because that’s far too late in the process; to make the right decisions, designers will have to start thinking in terms of building science. And, they’ll have to start paying closer attention to builder execution as well, because in many cases the builders will cut corners if left to their own devices – and this can lead to problems, regarding both regulatory compliance and the owners’ daily operational costs.

California’s Title 24 energy code has been mandating ever-higher levels of energy efficiency in residential construction since 1974. The latest tightening occurred just last January, when new energy standards went into effect. Now for the first time architects and their clients are really feeing the pain that comes with compliance: we’ve been telling them to use better performing windows, higher-efficiency systems, more insulation, and sometimes even HERS tests. All these items have their own measurements, architects need to  master the use of these measures until they’re second nature.

Some of our Title 24 clients, who are other residential architects, have very straightforward needs. They just want to comply with the requirements, period. Their clients are developers or homeowners who are basically motivated by expediency, and who don’t have a great commitment to sustainability. And that’s OK, because they’re still meeting a stringent baseline.

Others, however, have a greater interest in green building for its own sake. Even here their interest are wide-ranging: energy-efficient buildings, renewable energy, resource conservation, reduced fossil fuel output, grid independence, non-toxic homes, habitat preservation, adoption of better living patterns and habits, improved physical health, and reducing waste. Some are seeking official certifications such as GreenPoint Rating, LEED, or even Passive House certification. (Net Zero Energy isn’t a “certification” although it is a sort of yardstick.)

The top house is a typical developer product, built to meet the minimum energy standard - whatever local standard is currently in force. The lower house is a LEED certified project, and would likely exceed any local energy code. However, both would be equally subject to Title 24 standards if built in the State of California.

And yet, many designers have a hard time with concepts such as “building envelope surface area” or “window U value” and I realized after a while that they’re simply unused to thinking in these terms. They weren’t graded on these things in school, and I don’t think the California architectural licensing exams have a section on energy – the closest they get to engineering is the dreaded Lateral Forces section that has to do with structural strength.

Myths About Green Energy Design

We’re still dealing with a very simplistic thinking. Here are some myths that I used to believe before I read the books.

• Passive solar design is a fabulous one-size-fits-all solution.
• Every home should have a radiant barrier in the roof.
• Straw bale homes are the answer.
• No, no! The Passive House standard is the only way to go.
• Everyone should switch to solar power today.
• No, no – it’s better to focus on building better, more efficient conventional heating and cooling systems.
• Radiant heat is the best way to go.
• No, no – all-electric Net Zero homes are the best!
• Green is all about having bamboo flooring and never flushing your toilets.
• Green is all or nothing. Don’t bother with that unheated yurt if you’re still eating meat.

Building Science is Measurable and Performance-Based

What’s wrong with these statements other than their obvious stupidity? None of them measures the actual performance of real homes, or attempts to take multiple factors and conditions into account. It’s like trying to cure every physical ailment by taking Vitamin C without identifying the cause of the problem. And trying to solve the right problems using the right means is what building science is about.

Concepts that come up most frequently in home energy discussions include:

• Conditioned space. This is the floor area (and volume) within the house that is subject to heating and cooling, also called “habitable space”. This is different from Gross Floor Area that’s usually shown on the permit submittal. Conditioned floor area excludes garages, attics, and unheated basements that aren’t lived in. It is very important to consider which areas will be conditioned and which not, and to provide a way to firmly close off conditioned space.

• Building envelope. Usually this means the exterior surfaces of the building, but for energy modeling purposes, this envelope may include some unconditioned space as well. However, the performance of this envelope including insulation and air infiltration, has a big influence on energy efficiency. An efficient envelope limits air leakage and has no gaps in insulation that could result in unwanted heat loss.

• Opaque surface. Any surface that is not a window, like a wall, roof, floor, or door, is an “opaque surface”.

• Openings. An opening is either a window or a door. If the opening isn’t covered but is fully open to the outside, the room behind it is a porch and isn’t considered as conditioned space.

• Glazing. Anything with glass, including windows, skylights, and sliding glass doors. The total area of glazing is a major influence on energy efficiency, as is the ratio of glazing to conditioned floor area. In Title 24′s “standard design” this ration can’t be greater than 20%. In other words, if you have a house with 2,000 SF of habitable space, the Title 24 baseline assumes no more than 400 SF of glazing – including skylights.

• Heating load. This is the amount of energy it takes to keep the house a warm toasty 72 degrees in the winter. It takes more energy to heat a home in a cooler climate than it would for the same exact home in a warmer climate. If that home is leaky and uninsulated, it will also incur a higher heating load, no matter where it’s located.

• Cooling load. The amount of energy it takes to keep the house cool in the summer. Like heating, it’s a function of house efficiency and also its geographic/climate zone location.

• Water heating. The amount of energy it takes to supply hot water to the home, based mainly on the efficiency of the water heater itself.

Building Science Is No Longer Optional

It’s funny that I’m writing this article since I have no training in building science other than using the Title 24 energy modeling software. Then again, if I can learn it, anyone can, so let’s try to make this a fun excursion. Title 24 has been described as “killing a mosquito with a mallet” so I’m not saying it’s perfect. But, the California Energy Center has spent a lot of time and effort trying to apply valid principles across a broad spectrum of conditions, with input from numerous engineering experts and organizations – so it’s not “made-up”.

But, the CEC also knew that if it made everyone calculate their home’s energy use by hand, nothing would ever get done. So, they developed a few software programs to speed the analysis, and you don’t need to be a rocket scientist to use these programs, either. (You just need to be patient, methodical, and have a high tolerance for repetitive, detail-oriented tasks.) Here at Green Compliance Plus, I’m the one that does most of the modeling, and I spend a lot of time trying to get our clients (other architects) to understand how to think about building performance, and what influences it.

This depth of understanding used to be optional, but now even basic designs are not passing Title 24 without additional measures. Designers have to know what these measures are in order to determine whether or not it will work on their project. And, designers have to start anticipating energy needs upfront far more than before, to avoid unpleasant last-minute surprises. Why? Because if you don’t pass Title 24, you can’t get a building permit. It’s as simple as that.

Sometimes designers ask us over and over why they can’t just do X, or they say, “But I can’t do any of the things you suggest!” It is sometimes hard to explain that no matter how I run it, I can’t get rid of some necessary energy feature – not without adding six other measures that by themselves aren’t as effective. It’s because the Title 24 standard itself is a constant and unchangeable constraint. You have to meet or beat this standard, and that’s all there is to it. No shoes, no shirt – no service.

Models as Essential Tools

Images like these are both generated by computer models showing airflow (left) and air turbulence caused by a jet engine (right), to visualize forces that normally can't be seen directly with our eyes.

A “model” is really “a way of looking at the world” or a specific aspect of the world. Models and theories are used to predict things, and they’re verified by tests in a laboratory or elsewhere. A model attempts to take into account all the possible conditions that would influence a specific outcome. Software models make it possible to make predictions based on a greater number of factors. Then you can test each factor one at a time. There are software models for all sorts of things, not just physical phenomena.

Models can be physical, or written sets of instructions, or software. Software models in general have three parts:

• Inputs
• Instructions to the program itself on what to do with the inputs
• Results

It’s a “black box” in a way. The only thing you can change are the inputs. However, by testing different inputs carefully and doing multiple “runs” you can figure out what effect each input has on the results.

A model as a "black box" is illustrated by the famous thought experiment called "Schrodinger's cat", where an imaginary cat is placed inside a sealed box with a certain probability of demise every hour. The experimenter wouldn't "know" if the cat were still alive until the box was opened.

The Title 24 Software Models

In a nutshell, the Title 24 software model takes your information about a proposed design, calculates its projected energy use for an entire calendar year, and creates an “energy budget” showing how much energy the home will need to maintain comfortable heating and cooling levels. It then compares this proposed budget to a “standard design” that has certain basic characteristics (such as small windows and thick walls) but in other ways is the exact equivalent of the proposed design. This allows the program to compare apples to apples and is a bit fairer than expecting every new home to be under 1,200 SF and shaped like a cube. There’s no upper limit to the home’s size and/or energy budget, either.

The Title 24 software model compares your proposed design against a "standard design" that is fairly compact, with modest window areas. The proposed design can make up shortfalls in these areas by going beyond the minimum in other measures, such as adding extra insulation.

Because Title 24 is a regulatory, mandatory standard rather than an option, it’s heavily encumbered by a lot of bureaucratic rules. Any software program used to generate Title 24 energy compliance reports has to be approved by the CEC. The only use for the software is to get a building permit within the state of California, which is a limited, albeit captive market.

There are plenty of other energy models out there that are far better and more accurate than Title 24 for predicting a building’s energy usage. However, none of them are acceptable for demonstrating Title 24 compliance.

Title 24 Inputs: Walls and Windows

So let’s take a look at some of the major inputs for Title 24 energy modeling. We start with the conditioned floor area only – this excludes attics, mechanical rooms, unheated basements, garages, porches, patios, courtyards, and crawlspaces.

Title 24 energy modeling inputs include the total conditioned floor area.

Next we need surface areas of all “opaque surfaces” – walls, floors, and roof. Anything bordering between conditioned and unconditioned space is counted; for example, the bottom floor is counted, but middle floors or walls between rooms are not. If the house has a lot of interior courtyards that are open to the outside, or floors that aren’t stacked neatly one on top of the other, it can be a bit of a chore to identify all the opaque surfaces.

There should be separate entries for every flat plane, i.e., every wall, roof, floor. You’ll have at least four walls, one for each direction. Further distinctions could include walls of different thicknesses; If it’s a remodel where only some walls are opened, there should be separate entries for walls being opened vs. walls staying as-is.

Remodels sometimes have conditions where some walls have to be counted, but they’re not being opened up, and they may not have much insulation. We have found that it’s much better to insulate ALL walls to a minimum than it is to insulate a small area of work and ignore the rest.

Title 24 energy modeling inputs also include wall areas, broken out by insulation level.

Windows have a huge, huge impact. Windows are great at letting daylight in, but they’re terrible at keeping out the cold on a winter day. Ordinary glass is also terrible at blocking the heat from the sun’s rays in the summertime. The more windows a house has, the more energy it will take to both heat and cool. Glazing surfaces can be grouped by wall – however for remodels where the windows are mixed, or where some windows have shading overhangs, sometimes we have to model each window individually.

Each window must be matched to the correct wall area, along with its performance metrics: the U value and the Solar Heat Gain Coefficient.

Title 24 Inputs: Heating and Cooling Systems

Title 24 energy model includes settings for common types of heating and cooling systems found in California homes. Each has its own efficiency measure, which can impact Title 24 energy compliance.

In addition to the surfaces, rated efficiencies of the heating and cooling systems are key. Different system types include gas forced air, hydronic, split system or heat pump. The difference between an ordinary gas furnace and a high-efficiency model can determine whether a home passes or fails. For a home that’s not passing, sometimes the simplest measure is to replace an older furnace even if you hadn’t planned on doing that.

Title 24 Inputs: Location, Climate, and Orientation

The home's latitude and solar orientation will impact its energy requirements, because the sun will shine at different angles and for different amounts of time depending on the season.

The home’s compass orientation (used in calculating passive solar benefits), city, and California climate zone are all required. The same house would incur different heating and cooling loads in Death Valley than in Tahoe.

Although solar orientation is a key principle in passive solar designs, it’s often not possible to optimize this if the project is a remodel, or is on a very small and predefined urban lot. I don’t think solar orientation has ever been a consideration in the laying out of streets or city lots, except to keep things on a north-south grid; most homes seem to be built to achieve maximum use of the lot, regardless of whether the sun shines inside or not.

For the purposes of Title 24 energy compliance, California is divided into 16 climate zones. The same house could perform well or poorly depending on the climate zone - and, something like solar orientation could help in one climate area more than in another.

Deep within the Title 24 software model are seasonal climate data for 365 days by region, which you cannot change.

What’s Not In the Title 24 Energy Model?

The Title 24 energy compliance software model has some intentional omissions that, for real-world purposes, one might want to include in setting a home’s energy budget. I’m not going to argue these points, but they should be noted for any brave readers who’ve actually gotten this far into the article.

Occupant behavior and preference. The house is modeled as if everyone keeps it at 72 degrees Fahrenheit during the winter day and night, and cools it to 68 in the summer, and no one ever goes on vacation. This is based on the ASHRAE comfort standard, which does have good reasoning behind it. In actuality, some people turn the heat down at night, or prefer not to heat the home so much.

Landforms. This is the single biggest omission which sometimes brings grief to projects that in the real world would be quite comfortably shaded by nearby mountains or hillsides. Title 24 treats every house as if it sat on a flat plain with no trees, landforms, or surrounding buildings. Thus sometimes it shows artificially high cooling loads. I can understand not counting another building, which could get torn down someday, but MOUNTAINS? Maybe they can’t figure out a foolproof way to do it, or how such a condition could be documented.

Fuel source (renewable or conventional). Title 24 is a measure of efficiency, but it doesn’t care much if you use renewable energy or gas. The thinking is, you should still build an efficient house, period, whether or not you cover the roof in solar panels. And, making the design efficient will reduce the number of panels you’d need anyway. However, the Title 24 manual itself states that one of the main goals of California energy policy is to reduce fossil fuel omissions AND to reduce strain on the utility’s power grid and infrastructure – since you have to do Title 24 whenever you change even part of a conventional heating system, I don’t see why they can’t reward self-generated power.

Appliances. For Net Zero Energy homes, Energy Star, and Passive Houses, part of the design process is to create a detailed energy budget that includes major appliances. Maybe even all appliances, large and small. Title 24 doesn’t care about your dishwasher or dryer, but your choices of equipment and when you choose to operate them can impact energy bills, so it’s still important for real-world consideration.

Green Building. There are energy efficiency standards, and then there are green building standards, and they’re not exactly the same thing. Title 24 could care less about VOCs, formaldehyde, or mold, because none of those conditions impacts energy use. Same goes for water conservation; landscaping and internal water consumption do not factor into Title 24 energy compliance. Other factors not considered include construction waste, habitat conservation, or proximity to public transportation – none have any effect one way or the other on heating and cooling within the building envelope. (It’s too bad about the public transportation – that one would be easy to put into the software model as a small additional credit.)

How Close is the Model to Reality?

The first thing is, Title 24 energy compliance isn’t intended as a predictor of real-world energy use or even comfort. The only intention is to compare all proposed projects to a standard to minimize energy-hogging features. One of the Title 24 models, Energy Pro, does include some cost-saving analysis and return on investment comparisons between different energy measures.

However even the most detailed prediction is just an educated guess. True energy nerds have been known to obsessively measure every aspect of their home’s actual energy use and temperature levels, in order to test their own assumptions and designs. A lot of today’s best solar designers were DIY experimenters in the 70s and 80s, and many of them freely admitted that their early mistakes were their best teachers. Building science itself is an evolving field. For example, air infiltration wasn’t originally recognized as being such a major factor in energy performance as it is now.

Thermal imaging can show where a building (or any body) is emitting the most heat. It can also show things like leaks or gaps in insulation, that otherwise wouldn't show unless someone opened up the wall. Those hot spots might be areas to consider for energy-efficiency upgrades.

The moral of the story is, don’t expect to get all the answers, because there will always be room for further discovery. Most of the green design practices of today are options with a cumulative effect: things you CAN do, but you don’t HAVE to use them all every single time. Each one should still be considered for appropriateness within each project.