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Spray Foam Insulation Is Not a Magic Bullet

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

Posted on Mar 8 2013 by Carl Seville

In case you haven’t noticed, I’ve been pretty hard on batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. 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 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. 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 LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. , 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-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. 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 sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. 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.

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Mar 8, 2013 9:39 AM ET

Thanks Carl
by Armando Cobo

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

Mar 8, 2013 9:57 AM ET

Infrared & spray foam
by Allison A. Bailes III, PhD

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

Mar 8, 2013 10:37 AM ET

Foam Question
by Ron Keagle

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?

Mar 8, 2013 10:50 AM ET

Thanks for the feedback
by Carl Seville

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.

Mar 8, 2013 10:56 AM ET

by David Meiland

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

Mar 8, 2013 11:01 AM ET

problem with SPF is mainly
by Jin Kazama

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 ...

Mar 8, 2013 6:22 PM ET

Addressing the Gap
by Oliver Curtis

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.

Construction Process Risk Assessment.jpg

Mar 8, 2013 8:59 PM ET

So who do I trust?
by Rob Fisher

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.

Mar 8, 2013 10:02 PM ET

Rob: in zones without very
by Jin Kazama

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

Mar 9, 2013 2:52 PM ET

Response to Jim
by Rob Fisher

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?

Mar 10, 2013 11:03 AM ET

Here in North Florida
by Curt Kinder

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.

Mar 12, 2013 9:58 PM ET

Edited Mar 12, 2013 9:59 PM ET.

Carl, it is hard to agree
by aj builder, Upstate NY Zone 6a

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.

Mar 13, 2013 9:53 AM ET

A view from old Europe
by Kay Mees


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.

Mar 14, 2013 6:32 AM ET

Disadvantages of Foam spray
by Amanda Dawson

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.

Mar 14, 2013 3:25 PM ET

Same Story; Different Material
by Gerard Celentano

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.

Mar 15, 2013 6:40 PM ET

Squirt foam insulation
by Clayton Mahan

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.

Nov 13, 2013 8:50 PM ET

SPF releases global warming gases
by Lucyna de Barbaro

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.

Nov 20, 2013 10:00 AM ET

Another problem - can break down over time
by Elizabeth Warren

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!

Nov 20, 2013 10:39 AM ET

Response to Elizabeth Warren
by Martin Holladay

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.

Nov 21, 2013 10:26 AM ET

reply to Martin Holladay
by Elizabeth Warren

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

Aug 5, 2014 3:37 PM ET

Air Sealing Verification
by chris albrecht

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.

Aug 5, 2014 6:01 PM ET

Response to Chris
by Carl Seville

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.

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