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 barrier. The building enclosure should completely surround the conditioned space, 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-value 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 test 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 gain.
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.
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