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Spray Foam Insulation Is Not a Cure-All

Poor installation can negate the benefits of this popular insulation

Posted on Nov 13 2013 by Allison A. Bailes III, PhD

Spray foam insulation is a great product. Homes insulated with it can be some of the most efficient and comfortable homes built. I've been in plenty of homes insulated with spray foam and can tell you that, when done well, those homes are airtight and comfortable. I’ve also seen homes where the spray foam was a waste of money.

Spray foam and the building enclosure

Spray polyurethane foam comes in two flavors, open-cell and closed-cell, and provides both parts of the building enclosure — the control layers for heat and air, also known as insulation and the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. The building enclosure should completely surround the conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , and the insulation needs to be in contact with the air barrier. Since spray foam is both insulation and air barrier, proper alignment of the insulation and the air barrier is guaranteed.

What's not guaranteed, however, is that all spray foam homes will be efficient and comfortable. It seems that some folks in the industry think the magic is in the product, that spray foam is a cure-all, but sadly, they’re wrong. Let’s take a look at four of the most common installation problems with spray foam insulation.

1. Spray foam isn't thick enough.

This may be more common with closed-cell foam, but it happens with open-cell foam, too. Since closed-cell foam has a higher R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. per inch, installers generally spray 2 inches in walls and 3 inches at rooflines to meet the minimum energy code requirements of R-13 and R-19, respectively, here in IECC climate zone 3. (Putting R-19 at the roofline is allowed under the UA tradeoffs rule in the IECC. See the Energy Nerd's blog on this topic if you want to argue.)

Open-cell foam usually fills the framing cavity completely, so it's easy to tell if the installer has sprayed enough. Closed-cell foam normally doesn't fill the cavity, so you've got to spot check in a bunch of places to make sure you don't get shorted.

The video below is from a house near Charleston, South Carolina that I visited in 2010. You can see that the homeowner in this case didn't get his money's worth. I knew immediately when I walked into the attic that something was wrong because it was too hot up there on that June afternoon. In a properly insulated spray foam attic, the temperature won't be much higher than the house temperature.

The problem was that the installer was doing his first spray foam job ever, and the thickness of the insulation varied from zero (visible roof deck) to about 9 inches. Unfortunately, good average thickness doesn't cut it. The coverage needs to be uniform because a lot of heat will go through the under-insulated areas. (See my article on flat or lumpy insulation performance.)

2. Spray foam installers missed some of the air leakage sites.

Once I got a call to look at a 10,000-square-foot house that had spray foam throughout, but the owners had a serious problem their first summer in the house. When I arrived, they took me to the master suite, where two towels were on the floor — to catch the rain falling off of the supply registers in the ceiling!

The problem was that the installers missed some areas at the soffit in the attic above the master bedroom, and gaps around the tray ceiling allowed the humid air into the room, where it naturally found the cold surface to condense on.

As this example illustrates, it's important to seal the enclosure completely. One of spray foam's biggest selling points is its air-sealing ability, but it can't seal places where it's not sprayed. One of the nice things about using spray foam in new construction is that you can do a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. before the drywall goes in. You also can test for leaks with a fog machine, as Martin Holladay described.

3. Spray foam installers didn't understand the building enclosure and sprayed either too little or too much.

In complex houses, seeing exactly where the building enclosure is (or should be) can be a challenge. If the installer misses areas, it may or may not be an air leak, but it will definitely be a thermal bypass because of the lack of insulation. Every part of the building enclosure must be insulated, or the home will have excess heat loss or heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss..

Another problem I've seen is that the installer sprays extra foam because they haven't identified the location of the building enclosure, the boundary between conditioned and unconditioned space. In photo 3 below, that wall with foam all over it has conditioned space on both sides. The homeowner paid extra and got nothing for it.

4. Spray foam contracts and pulls away from the framing.

Photo 4 below shows how the closed-cell foam in a new house had pulled away from the framing in many of the wall and ceiling cavities. The same thing can happen with open-cell foam, too. Some of the reasons for it are a bad batch of chemicals, improper mixing, foam temperature too high, or substrate temperature too low.

Whatever the cause, it's not a good thing. A little bit of uninsulated area like that adds up to a lot of heat loss or gain when the whole house has that problem, as it did here. Again, see my article on flat or lumpy insulation.

The sum and substance

Don't assume that just because a home is insulated with spray foam that it's automatically a winner. As I said above, spray foam insulation is not a cure-all. Every product has its pitfalls, and spray foam is no exception. The good news, though, is that spray foam's problems are generally infrequent and easy to overcome with proper training, planning, and follow through.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.

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  1. Energy Vanguard

Nov 13, 2013 9:52 AM ET

Global Warming Potential
by Daniel Beideck

An important factor to consider when selecting what insulation product to use, in my opinion, is the global warming potential of that product. Presumably, one of the reasons we should be insulating our homes well is to minimize the greenhouse gasses emitted when we heat or cool our homes. However, we also need to consider the greenhouse gas emissions of the products used to insulate the home. Some of the blowing agents used in closed cell blown insulation are very nasty greenhouse gasses that are orders of magnitude worse than CO2. For HFC blown closed cell spray foam, it can take decades for the savings in greenhouse gas emissions from reduced heating/cooing of the home to make up for the initial damage done to the spray foam itself!

Nov 13, 2013 10:15 AM ET

Edited Nov 13, 2013 4:15 PM ET.

Nov 13, 2013 10:20 AM ET

Response to Daniel Beideck
by Allison A. Bailes III, PhD

Alex Wilson has done a tremendous service to the green building community with all the research and writing he does on the nature of the many green building materials we have to choose from. The article you referenced, however, is not his best work. I took issue with his methodology and his results shortly after he published it. You can read it on the Energy Vanguard website:

Don't Forget the Science in Building Science

He certainly had grounds to recommend against certain types of foam insulation, but he went too far in trying to put mathematical authority behind his words. And I'm not the only one who thinks so.

Nov 13, 2013 11:00 AM ET

Resonse to Allison Bailes
by Daniel Beideck

Allison, I had previously read your article and you have some valid points. As a physicist myself, I understand that the work that Alex Wilson presents is not peer reviewed science and is based on some (reasonable in my opinion) estimations that the blowing agents used are likely to be ones that are nasty greenhouse gasses and that half of the gas eventually escapes to the atmosphere (and half doesn't). It would be wonderful to have rigorous measurements of these materials emissions. However, to the best of my knowledge we don't. We are building new homes, offices etc every day and that isn't going to wait until someone makes those measurements. The best we can do is work with the best understanding that we have now, and the best understanding that we have is that some insulation materials are likely to have a much greater global warming potential (GWP) than others. It would be justifiable, in my opinion, to still use those materials if they ultimately saved more CO2 equivalent then they emitted AND there were no reasonable alternatives. However, there are many insulation materials and methods that have much smaller GWP risks that will do the same job in the vast majority of cases. Those ought to be used whenever possible, in my opinion, until we have good reason to believe that the products that Alex identified do not have the high GWP estimated.

Nov 13, 2013 11:51 AM ET

Response to Daniel Beideck
by Allison A. Bailes III, PhD

Daniel, I agree with everything you said and concluded my article with what Alex should have said:

Some insulation materials MAY use blowing agents with a high global warming potential, and IF those chemicals escape, it COULD be bad news for climate change, depending on how rapidly they're released and what kind of construction they're used in and where the building is. Then again, maybe it's NOT a problem and using them actually helps mitigate climate change. Based on the Precautionary Principle, however, we advocate avoiding these materials until it's certain that the blowing agent has a low GWP.

My beef with the article was his making it look more authoritative than it was. In addition, the blowing agents have changed since he wrote the article in 2010, so I don't think it's so easy to condemn foam now based on GWP.

Nov 13, 2013 4:29 PM ET

Closed cell foam between studs & rafters is wasted.
by Dana Dorsett

To paraphrase a Clinton-era campaign theme: "It's the thermal bridging, stupid!"

When you put 2" of closed cell foam in a 2x4 cavity, you end up with a 2" thermal bridge through the framing, rather than 3.5". This results in a LOWER performance wall assembly than R13 as fiber or open cell foam due to the dramatically higher thermal bridging. And this is not a subtle difference either. It meets the letter of code, but it is a serious step down the performance ladder:

At a typical 25% framing fraction an R1.2/inch wood an R13 fiber-filled 2x4 wall, with OSB sheathing and wood siding, with half-inch wallboard adding up to about R1, has a "whole wall" R of about R9.5.

The same wall with 2" of R6.5/inch (R13, center cavity) closed cell foam comes in at about R 7.2 whole-wall, about a 25% reduction in performance.

The hit in due to the much shorter thermal path (2" instead of 3.5") of the R1.2/inch wood penetrating the foam. Wood being about 5x as thermally conductive as closed cell foam is serious performance-killer at any thickness- bump the foam thickness to 3" and it'll hit ~R10.3- less than an R1 improvement over a full fill of open cell, an R0.8 that comes at a significantly higher cost.

A 1" layer of R6.5/inch polyiso sheathing between the structural sheathing and siding on an R13 fiber (or open-cell) studwall comes in at R16 whole wall a 70% improvement over the fiber-only studwall, and more than twice the performance of the 2" of closed cell, for about the same (or slightly lower) cost.

Bottom line: Save the high-R/inch foam budget for foam sheathing, where the performance is not undercut by R1.2/inch framing, and put the cheap stuff in the cavities.

BTW: Alex Wilson may not have done the math with any rigor and overstated the case, but the essence of his point on the net destructiveness of high GWP blowing agents is not wrong. HFC134a has (rightly) been banned for most purposes in Europe (where the CO2-blown XPS has about the same R-values as EPS of the same thickness and density), and I suspect HFC245fa is on it's way out too, now that there are multiple competing low-GWP blowing agents on the market. In the mean time, water-blown ~2lb polyurethane is pretty good (Icynene has a couple of options, as does the regional player Aloha Energy.)

Nov 13, 2013 10:54 PM ET

Edited Nov 13, 2013 10:57 PM ET.

Thermal bridging (response to Dana)
by Harry Voorhees

Dana's point about thermal bridging took me a few minutes to understand, so maybe this explanation will help others. Basically if you put only 2" of insulation in a cavity then the conditioned (i.e. warm in winter) surface is only 2" away from the unconditioned (i.e. cold) surface. Therefore, that delta-T spans only 2" of the framing, so the framing conducts more heat than it would if the entire cavity were filled with insulation and the delta-T spanned the entire framing width.

So I suppose the other possible takeaway is: if you flash, then also fill ?

Nov 14, 2013 1:04 PM ET

new GWP estimates?
by Daniel Beideck

Does anyone know what the revised GWP is for closed cell insulation (and XPS?) using the new blowing agents? It would be nice to know if the changes were incremental or do they make changes sufficient to make them comparable to the alternative insulating products?

Nov 14, 2013 1:17 PM ET

Response to Daniel Beideck
by Martin Holladay

According to Tristan Robert's 2011 article on the topic, the new blowing agents from Honeywell have a GWP of 7.

Nov 15, 2013 8:18 AM ET

new blowing agents and same old poisons
by Ken Levenson

Yes, Honeywell may have developed a low GWP blowing agent - but is anyone actually using it? Anybody claiming to use it? Might be more useful to know than "it exists".

Another serious failure of spray foam is the toxicity to the environment, occupants and the workers. OSHA is actively investigating it for work place safety. The manufacturers are facing class action lawsuits from building owners that cannot occupy their buildings. And whether the toxic bioaccumulative ingredients are released into the environment in onsite manufacturing or over the life of its use or when it is finally put in the landfill it's not green nor sustainable - just a great marketing achievement by our friends at Dow Chemical and other such (not)stewards of the environment.

Talk of reducing bad effects of blowing agent or fire retardants is all for the better and should happen, but until the MDI is removed from the spray foam it should be treated like the toxic garbage it is. I'd like to hear how Dow Chemical is planning on removing the MDI. Any clues?

Maybe if we had no other alternatives, spray foam would make sense as a high-performance material. But we do have alternatives - truly green, sustainable and high-performance alternatives. They should be considered before one considers spray foam.

Nov 15, 2013 11:39 AM ET

Yes, fill those framing cavites! (response to Harry Voorhees)
by Dana Dorsett

You've got it! Wood is more thermally conductive than fiber insulation (or air), so the effect of having a stub of framing that isn't surrounded by insulation is that of a heat-sink, presenting a higher surface area of the more-conductive material to the conditioned space, and a shorter/lower-R thermal path through the insulation (the thinner shot of foam.) In the 2" foam in a 2x4 cavity case, instead of the 1.5" width of thermally conductive wood on the conditioned side you now have 4.5", and instead of ~R4 of thermal bridge you now have ~R2.

The three-dimensional thermal model isn't simple, but even a 2-D approximation is good enough to demonstrate the severity of the problem.

As for the new-improved lower greenhouse HFC blowing agents, yes they exist, no they are not in widespread use. HFC245fa is still by far the dominant blowing agent in the 2lb foam market. I haven't heard of any major players in the US market moving over to Honeywell's Solstice- it may tak a regulatory ban on high GWP blowing agents to force the transition.

But the water-blown goods from both Icycene (a large player in the US & Canadian markets) & Aloha Energy (a regional player in the US northeast) are out there and real. For those who care it's only a matter of chasing down a local installer (more difficult in some regions than others.) While massive use of spray polyurethane carries the other environmental impacts, there are many applications where judicious use can still have a lifecycle net benefit, where the air-sealing and vapor retardency optimization through the use of these materials can enable simpler high-R assemblies.

Nov 16, 2013 1:57 AM ET

Not a Cure All
by Francois Theriault

Sloppy, toxic, shrinks..... how about smell. Like dead fish. For two years after the install. "Properly installed" is the key. A competent installer with years of experience is the only way to guarantee effective insulation with any material.

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