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Green Building Curmudgeon

Spray Foam Insulation Is Not a Magic Bullet

It’s time for me to bad-mouth something besides batt insulation

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Too often, foam insulation is installed too thin, and the problem is not corrected before the foam is covered up.
Too often, foam insulation is installed too thin, and the problem is not corrected before the foam is covered up. Foam installed around open web trusses and roof ridge beams is often susceptible to gaps. These must be identified and corrected before the work is covered up for effective insulation and air sealing. In this otherwise well built project, the spray foam insulation was so poorly installed that it didn't meet the energy code and in some places the exterior sheathing was visible from inside the building. Neither the contractor nor the insulation installer were knowledgeable enough to identify these problems. Cured foam, both open and closed cell can pull away from framing members, leaving gaps that reduce the thermal efficiency and air sealing of the entire installation

In case you haven’t noticed, I’ve been pretty hard on batt insulation in the past. I feel that my complaints and concerns are well justified, but no matter which insulation product is chosen, it has to be installed properly or it just doesn’t work.

Many people mistakenly believe (myself once among them) that spray polyurethane foam (SPF) is the perfect product, is always installed right, and tightens up homes every time.

This is simply not the case. In fact, I am seeing more and more poorly installed SPF than ever before. Demand for SPF has increased, bringing more installers into the market, many without the necessary experience or quality control to provide consistent quality installation. SPF, and open-cell foam in particular, is frequently installed with large gaps where the fast-curing material folds over itself, leaving both exposed and hidden unfilled areas. Mix and temperature problems can affect its ability to adhere to framing. Cured insulation often pulls away from framing members leaving large gaps. Insulation is installed too thin. And finally, installers can miss whole sections, leaving large gaps in the air barrier that the insulation is supposed to provide.

Quality control needs help

While there are plenty of installers who have good quality control, in many cases, SPF has become yet another commodity product. Inexperienced contractors don’t understand that installation quality varies, and they often don’t know enough to evaluate the work they get.

I have inspected projects for LEED, EarthCraft, and other certifications where neither the insulation installer nor the contractor realized that the average installed SPF was several inches thinner that specified, had significant gaps, and in some areas, was missing entirely.

When I inspect homes, I stick a metal ruler in the foam to check the depth, pointing out the areas that are insufficient. More often that not, I see ½-pound open-cell SPF installations that average about 4 inches in rooflines and less than 3 inches in exterior walls. With an R-value of between 3.5 and 4 per inch, that means the installed R-value doesn’t even meet the energy code minimum.

Not unlike the contractors who install batt insulation, there is far too little supervision or quality control over SPF in the field, and the contractors who are paying for it don’t know enough to evaluate what they are buying.

Is spray foam for lazy people?

While I acknowledge that SPF is often the best solution for some building conditions such as floors over crawlspaces that must be vented, it is a petroleum product full of chemicals with significant environmental impact. I see it used in exterior walls where blown in fiberglass or cellulose, combined with sealing the exterior sheathing would work just as well.

Complicated building volumes, particularly vaulted ceilings and cantilevered floors are difficult to insulate and air seal with traditional materials, so builders resort to SPF, when simpler designs would allow them to use less expensive materials.

Even though SPF does solve a lot of problems with other insulation products, it isn’t magic and most of what it does, with some good planning and design, can be done just as well by alternative materials, often at a lower cost.


  1. Expert Member
    ARMANDO COBO | | #1

    Thanks Carl
    I wonder if you or other readers can post some thermal imaging pictures of these issues to drive your point even farther. Good post!

  2. GBA Editor
    Allison A. Bailes III, PhD | | #2

    Infrared & spray foam
    Armando, I ran a guest post in the Energy Vanguard Blog a while back that shows exactly what you're looking for. Here's the article:

    Spray Foam, Infrared Cameras, & the New Big Holes

  3. user-1140531 | | #3

    Foam Question
    If you rely on closed cell foam to perform as an air barrier, and if the foam shrinks and pulls away from framing members and opens cracks; will outward vapor drive in winter condense as it enters the dewpoint region of the cracks and fill the cracks with water suspended against the framing by the capillary action of the cracks on a prolonged basis?

  4. Expert Member
    CARL SEVILLE | | #4

    Thanks for the feedback
    Allison - appreciate the link to Jamie's post, I don't remember seeing that one. The IR images really show the problem.

    Ron - I suppose that in a cold climate you might see some condensation, but if you used foam sheathing or double wall framing to provide a thermal break it would be unlikely. In moderate climates it doesn't usually get cold enough to cause much of a problem unless the indoor RH is very high on the rare severe cold days.

  5. davidmeiland | | #5

    This has been discussed a few times on, and some really good images posted.

  6. jinmtvt | | #6

    problem with SPF is mainly
    problem with SPF is mainly the same as with batts .. installation

    Even an experienced sprayer can leave many unseen voids that can only be detected with IR or opening up the foam layer. Very hard to control, and everyone wants to do it as quick as possible ...

    It is not very popular here except for exterior insulated commercial buildings where error is easier to spot, and the area around the floor joists that sits on concrete ( joist rim? forgot the english term )
    where i have seem many many defective installed ( usually sprayed with green soya stuff here )
    leaving many corners opened, way to thin layers on the joists end stick etc..

    at least, it blocks air better than most bat installations i've seen, and prevents "most" of the condensation problems at this area we've been having since 80's here ...

  7. olcurtis | | #7

    Addressing the Gap
    I recommend everyone read Mason Knowles' September 2010 JLC article, "Troubleshooting Spray-Foam Insulation," for basic technical information and installation images. Expanding spray-in-place foam insulation requires chemical foam applicators to check and monitor the following list of variables (off the top of my head):
    - "A" side & "B" side temperature
    - foam ratio
    - mixing in the hoses and spray gun
    - line pressure
    - substrate temperature
    - substrate moisture content
    - site humidity
    - ventilation levels

    This list doesn't even include proper technique (lift, speed, pattern etc.), coverage or thermal boundary location. As an industry, we need to better explain the gap (see graph) between perceived and actual risk when dealing with not only highly variable but also difficult to reverse building products. As with most situations, this is a nonlinear function.

    Spray foam can be an effective product but it is definitely not a magic bullet.

  8. RobFisher | | #8

    So who do I trust?
    If the install contractor can make mistakes that I cannot see with my eyes how do I know if the work is done properly? Should I hire a 3rd party inspector? What should there qualifications be? Should they be there before?During? Or just after the install?

    As an architect I agree that spray foam is not a magic bullet, and most new construction can be designed to not include spray foam (often for the better). But where I see spray foams strength is in renovation work. Especially when there is exterior cladding that is sound or not easily removed.

  9. jinmtvt | | #9

    Rob: in zones without very
    Rob: in zones without very cold winters , spray foam alone and or with a minimal exterior insulation,
    even if defective in the installation, will not cause much harm.

    On the other hand, 6a to 8 ... risky business if you use the SPF alone or with very little exterior insulation.

    It is all a question of % of maximum potential problems.

    Leaving 1% open voids in zone 3-4 will only hinder insulation performance, where in zone 6-7 , a half inch hole toward sheathing could produce mold in a single winter.

    Olivier: man do i love your graphic!
    i will save it if you don't mind, and keep it for future use/reference :p

  10. RobFisher | | #10

    Response to Jim
    Jim, I understand zones and the potential problems. I am in zone 5, directly adjacent to zone 4. My current thought is to insulate between my roof rafters as the existing slate roof has at least 25 years of life left (according to my roofer). My concern is how do I ensure that the foam is installed properly? I can visually inspect but what about the potential problems that I cannot see. I assume I would hire an inspector with IR capabilities. But how do I know they are qualified to inspect/use an IR camera?

  11. watercop | | #11

    Here in North Florida
    We are big fans of foam for both existing and (what little there is) new construction. Given our climate issues I worry less about thin spots but a great deal about air sealing. It is all about keeping out high humidity outdoor air.

    Every foam job should be quality checked by a disinterested observer. We QC any foam we order, and a couple of the better foam contractors invite us in for QC so as to be able to assure the client the job is well done.

    We perform before and after blower door tests. We use theatrical smoke, typically 3 iterations, to identify gaps before the foam crew packs up.

    We just came off the local Home&Patio show, and the most compelling image on display at our booth was one of smoke pouring out of the eave of a house with a rotten foam job.

    A good IR is on my shopping list.

  12. wjrobinson | | #12

    Carl, it is hard to agree
    Carl, it is hard to agree with much of what you post. My spray foamed homes are an order of magnitude better than days of leaky fiberglass filled wals.

    I do like the new idea of sealing with spray caulks and or tapes, but with a good spray company which I have, I know it is the magic bullet compared to days before I used it.

    As with all subs, best to really know the sub and the product and the conditions needed to shoot foam.

  13. KayMees | | #13

    A view from old Europe

    I've been working in Germany and France in wood construction for a long time. SPF is not an option at all in Europe. Air sealing is being done either by OSB with joints sealed or by specific products as vapor retarding membranes on the inside.
    Insulation materials are never used for air sealing, this is always a different layer.
    Environmental concerns as well as technical risks are the reason why Europeans would be horrified by the idea of using SPF in these quantities. I think that for reasons of fire protection it wouldn't be admitted anyway.

    The best way to insulate a frame built house is to create cavities that are air-sealed inside and outside, and fill them with cellulose or some other wood fibre based insulation.

  14. Amanda_22 | | #14

    Disadvantages of Foam spray
    Like any insulation, there are pros and cons to spray foam. Spray foam insulation is more expensive than fiberglass insulation. The process isn't neat, and the foam can be accidentally sprayed into places other than the intended target. If too much insulation is sprayed in, walls that are thin might buckle as the foam expands. Safety also is a concern for anyone who is attempting to apply this type of insulation.

  15. gman571 | | #15

    Same Story; Different Material
    Can someone post a link to an analysis that shows how significant this is?
    I don’t think the R-value degradation is much. Let’s take a 2x6 stud wall with some insulation that equates to an R-19 in the center of the bay. As soon as you add 15% for wood, your R-19 degrades to an R-13.89. Throwing in an R-3 window (6% of the wall) brings you to an R-11.25. Assuming you have some outlet boxes (1% of the wall) that only have half the insulation behind them, then your R-value falls to 11.19. Now let’s say 5% of the wall has insulation installed poorly and is only an R-10, then your wall system R-value falls from 11.19 to 10.92. This poor insulation has cost you about 2.5% of your R-value. Differing materials change the numbers but the trends are the same.
    R-values (and U-values) are discussion points that they don’t tell us what we really want to know. What we need is an analysis which ties this to energy.
    I have a 2200 square foot house modeled in Manual J (colonial, 2 story in New England). If I degrade my U-factor by 2.5%, my estimated heat load degrades by two tenths of 1% (.002). This equates to 150 BTU, which is some number of teaspoons of oil (every year).
    I’m a novice at Manual J. However, even if I’m close, it shows this whole topic is not worth much.
    I’d be curious to read others’ analyses.

  16. firry | | #16

    Squirt foam insulation
    I found that some old foam had so degraded that the R value must have changed considerably. The shrinking and pulling away is also an issue when it is applied and even in its initial application can cause a shrinking or expanding action of other material due to its own purpose thus separating itself. It likes to adhere to itself better than some materials its against. Heat dissipation or cold dissipation can become an issue too if there is not the breathing factor that does dissipate temperatures. Dissipating of temperatures can prolong the life of many materials whose replacement cancels out the original intent.

    I find stuffing insulation can be greatly enhanced with squirt foam in seams, corners, behind outlet boxes, pipe and wire openings, vents and even some joints. Using solid panel foam and locking it in place with squirt foam is great too, to achieve higher R values while maintaining circulation space gaps for the protection of surfaces and their materials. Added use of squirt foam I find is a better approach than its sole use..

    I agree that it is over used and misused and often can create greater costs down the road a bit or in the event of any anticipated changes. It is like the structural panel application. It is good unless you may see the need to make alterations then you have a structural problem to deal with that may work against the concept of the original efficiency factor.

  17. lucyna99 | | #17

    SPF releases global warming gases
    There are many much more environmentally friendly materials to use. Blowing agents in SPF contribute to global warming. It is sad that people don't consider that aspect with sufficient seriousness. Per industry informal comment at the 2013 Passive House Conference, SPF w/blowing agents that don't contribute to global warming are expected to be available only around 2015.

  18. user-676906 | | #18

    Another problem - can break down over time
    Hi - another problem for readers' consideration...
    I used to work in a building (built c. 1961) which was insulated with spray foam (which is unusual here... I'm in Western Australia.) The building has a tiled roof, and when the spray foam was installed, it lifted the tiles as it expanded... which was fine until the foam started to break down (since the foam sealed the gaps it had created), but once the foam did start to break down, it created an absolute nightmare of roof leaks.
    ...maybe the product has improved over time - but I'd want an impressive guarantee before I used it myself!

  19. GBA Editor
    Martin Holladay | | #19

    Response to Elizabeth Warren
    Fortunately, few spray foam contractors are incompetent enough to spray foam directly on the underside of roof tiles.

    Such incompetence exists, of course -- in the U.S. as in Australia -- but fortunately, it is rare.

  20. user-676906 | | #20

    reply to Martin Holladay
    Hi Martin,
    Good to know! :-) Just thought I'd pass on that experience.

  21. ahiweather | | #21

    Air Sealing Verification
    Just finished doing Air Sealing Verification (ASV) on a spray foam contractor's work. This was actually the second ASV procedure to be done. We found multiple spots that they missed with the IR camera and the blower door operating on the first procedure. We returned to check it once again today. There is still a substantial amount of air entering the attic areas. This contractor is going to be very unhappy when I tell him that he should return to improve upon his past efforts.
    Neither the SPF contractor nor the homeowner would've had any idea that the job was this poor had they not contacted us to do the ASV procedure. I'll be surprised if the SPF contractor requests one again! This procedure should be required if you ask me. I've seen too many issues that have been instigated by inadequately sealed attics here in Climate Zone 3.

  22. Expert Member
    CARL SEVILLE | | #22

    Response to Chris
    I appreciate the report Chris. I do visual inspections of SPF jobs and almost always find gaps and thin spots. It seems like as the industry grows not surprisingly the workmanship suffers. And, too many contractors don't care enough about the things their clients can't see when they're done.

  23. cporrett | | #23

    Really, So here goes, Have built houses with whole house wrap and fiberglass insulation. ( which settles over time and creates air gaps and hot and cold spot. Used spray foam 7 years ago and had to open up a wall for a room addition. Guess what. it didn't settle at all. Still in place and twice as good at maintaining the heat as any of the old fiberglass insulated walls I ever did. I (Won't ever install fiberglass again in one of my homes. Foam is better at sound dampening the meandering moos in the back 40 as well. My son still hears them when they come up for feed in the cold months. My wife's View on fiberglass is (Build green not gross).

  24. vikihymer60 | | #24

    Spray foam is extremely dangerous! It totally ruined my house and cost is on me. Proven to be off gassing above legal limit, I tried to work with company to fix problem. It can’t be fixed. It was put on floor of attic stopping up soffits. Shut down whole house. Vents don’t work, propane hot water heaters no longer work, ducts are ruined, fresh air machine ruined, under house of pier and beam house messed up, just to mention a few. Health is severe with docs watching for cancer to develop. Poison gas is in house. But I learned this for people checking your house air- the poison will show up as paint off gassing. Both paint and spray foam have acetate and toluene thus confusing test results and home owners. If you suspect foam, test the foam itself. I think spray foam should be taken off the market, but it seems to be a protected industry. So what is a homeowner to do—DON’T use spray foam ever. There are much safer insulations on the market.

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