Most experts agree that spray polyurethane foam is a revolutionary product. What they don’t always agree on is the way it’s installed and integrated into a building assembly. To shed some light on this debate, energy-efficient building expert Bruce Harley (Westborough, Mass.) and architect Peter Pfeiffer (Austin, Texas) explain how they use spray polyurethane foam to insulate the homes they build.
No other insulation system I am familiar with provides the real R-value that spray foam does, accomplishes the air-sealing it does, or thwarts vapor flow as well. Closed-cell spray foam greatly reduces the chance for condensation within the framing of a home. I think it is critical that houses be built to thwart vapor flow correctly. I insulate all homes pretty much the same. However, in colder climates, I use 2×6 exterior walls, create a cold roof (drawing p. 36), and insulate the basement or crawlspace, Peter Pfeiffer of Barley & Pfeiffer Architects is a LEED-accredited architect and building scientist who has spent the past 30 years developing high-performance building-design strategies.
Spray foam can be a great material, but understanding its use is often hindered by overeager installers who emphasize the magic rather than the real properties of the products. Too often, I hear from clients that “my dealer said that I only need 2 in. to 4 in. of foam in my walls because it performs just like R-40 fiberglass and prevents any possible moisture problems.” It’s just not true. An R-12 wall is an R-12 wall, no matter what the material is. Cutting air leakage saves energy, but it doesn’t make up for a low R-value. For best performance, I use spray foam in a variety of ways when designing the shell of a home. Here’s one example. Bruce Harley of Conservation Services Group is an energy-efficient construction expert and author of Cut Your Energy Bills Now (The Taunton Press, 2008).