Building Science for Residential Architects

Building Science for Residential Architects

Posted on 18. Jan, 2011 by in Designing for Compliance

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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.

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About the author
 Rebecca Firestone has been working in the Bay Area since 1998 as a technical writer, business content developer, architectural filing lady, marketing director, and sorcerer’s apprentice.


One Response to “Building Science for Residential Architects”

  1. Northern CA designer

    06. Apr, 2011

    As a designer, I can’t say enough good things about Randall Whitehead’s Residential Lighting, A Practical Guide. This is his follow up to his wonderful Lighting Up! A Practical Guide which has been a staple of the design community for seven years. All the best parts of the earlier book have been retained with the addition of more than 200 photos in both color and black & white.

    The chapters have really been packed with up-to-the-minute information about many of the new technologies that are now becoming the norm, such as light emitting diodes (LEDs). There are also a whole new series of enlightening sections in the back of the book with great tips on how to run a design business, how to get published and how to deal with clients.

    Randall’s way of writing is very entertaining and I feel it has revitalized the often dry category of textbooks. His funny, casual method of doling out information really helps make this book a pleasure to read. His energy and humor is infectious as he lets readers in on the secrets and practices of good lighting for homes and gardens. What also sets this book apart from other texts on lighting is how he approaches the subject first from the aesthetic side then gradually lets the reader in on the technical reasons how lighting design works.

    This is an inspirational reference guide for all aspiring designers… as well as for established design professionals like me. Even savvy homeowners will latch onto this book as the insider’s guide to the secrets of great lighting.

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