Home Insulation and Title 24

Home Insulation and Title 24

Posted on 21. Feb, 2011 by in Building Techniques, Insulation

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.


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.

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6 Responses to “Home Insulation and Title 24”

  1. That looks nice. That is really good in hot countries like ours. Thanks for the informative post. I’ve learned a lot from it.

  2. clean energy

    14. Dec, 2011

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  3. Mark

    22. Jun, 2013

    You have shared an informative post about insulation with photographs, this post surely will be helpful for every person who wants to make there home more comfortable and save energy bills, and your project is really great many thanks for sharing…

  4. Orlando Roofing

    22. Nov, 2013

    Greta post with indispensable information on the do’s and don’ts of insulation. It truly does make a difference in the efficiency and comfort of a home.

  5. […] echoed a sentiment that we’ve heard from a few other people, namely, that voluntary certifications don’t do that much to save the planet because the bulk […]

  6. Scott Adams

    11. Oct, 2017

    I like that you talked about how cotton batt is recycled, so it helps the environment. I have been looking for insulation to use in my new house. I can see how it would be nice to use cotton batt so I don’t feel like I’m hurting the environment.

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