“Think Things Through” before using Spray Foam
This one piece of advice: “think things through” would have saved me a lot of trouble!
In 2010 I rehabbed a home that was gutted after Hurricane Katrina, and spray foam was a new thing. I decided to contract with a company that claimed it invented a “green” product that used sugar cane as a base for its spray foam. Although it was more expensive than fiberglass, spray foam seemed like it was the much better choice for energy efficiency. The foam did seem to save energy as the owner claimed, and it seemed to stop air infiltration (I knew that because when the AC kicked on, doors slammed shut, moving air from one room to another instead of drawing air from outside the home). However, because the attic was unvented, moisture from the house tended to accumulate there, and guess what else liked moisture: termites. The US gulf coast climate is termite heaven, and I believe that spray foaming structures there is a big gamble, unless it’s a steel building, because small roof leaks can go undetected for more than enough time to establish a large termite colony. I did get a quote on fiberglass insulation, and in retrospect wish I had heeded that businessman’s sage advice: the home was circa 1950’s, in excellent structural shape, and did not have spray foam installed before. Changing up the insulation and “envelope” of the home can (and did) have serious consequences if you don’t “think things through”. Here is some wise advice to several homeowners who were considering sprayfoam in northern states.
It can cause moisture to build up in the attic
One homeowner in climate zone 6 A (the eastern blue zone on this map) - where it can get down to -26F at times–encapsulated his attic roof with 2-inches of closed cell spray foam (ccSPF) because of the AC ducts. The AC worked great, but there was an unintended consequence.
The attic started to build up water vapor to 70 to 80% at times. He mitigated the issue by installing a dessicant dehumidifier which exhausts out on the side wall of the attic. This keeps the attic around 40% RH….Nothing wrong with ccSPF, but you need to think things through.
It doesn’t give more R value
Bill Wichers, an Expert member of greenbuildingadvisor.com, advises that two inches of closed cell spray foam (ccSPF) is about R12 (reality), or up to around R14 (marketing), and no more than that. This is way below code (which is now R60 in most Northern climate zones (CZs)). The problem is that spray foam companies tend to distort the R value of spray foam, to being better than "regular" R value because of air sealing. However, R value is R value, period, and should not be confused with air sealing. The homeowner needs more R value in the attic, especially in such a northern CZ.
(In response to the moisture issue above, Bill Wichers added that if the attic is inside the building envelope, then you can recirculate the air from the attic into the rest of the home and thus reduce the moisture in the attic.)
It has “holes” and can offgas undesirable VOCs
Douglas Horgen, a contractor and member of greenbuildingadvisor.com, advises that in his personal opinion, spray foam is one of the riskier options. It's easy to make mistakes (in mixing and application), and they are consequential and expensive to fix. Although he generally prefers to avoid it, in his remodeling work he ends up using it regularly. They hire one company with elaborate quality control processes and they supervise it well, check for and repair the missing spots (there are always missing spots), and even with all that, we have a product full of fire retardants and other stuff that does get into the home environment. Therefore, spray foam has its place, but also has its risks.
Don’t fall for “green”
Oh, the naivete of some people… including me. According to Dana Dorsett, another expert member of greenbuildingadvisor.com, the "soy" or “sugar cane” content of "bio-based" foams is really but a fraction of just one of the two components that are mixed, and only amount to something like 15% of the total content of the product by weight. It's really just green-washing marketing. Where applications might call for closed cell foam, selecting a product with a low-impact blowing agent would have far greater environmental impact than the fraction of plant-sourced components of the polymer production. For more on the ingredients of spray foam, check out our article.
Photo by Ömer Haktan Bulut on Unsplash
