Spray foam in roof deck — Is lower R-value than minimum code recommendation OK?
drrossw
| Posted in Green Building Techniques on
I am remodeling a 106-year-old home in Climate Zone 4A where the minimum recommended attic value is R-38. A local spray foam contractor, with a large national company, told me that with spray foam a much lower R-value is OK. He quoted the job at R-20 for the roof deck. I know that air sealing is of paramount importance but it seems R-value also is important.
Is R-20 really enough?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Ross,
Q. "Is R-20 really enough?"
A. No. R-20 is less than the minimum R-value required by code. The only reason that the spray foam contractor is recommending less than the minimum R-value required by code is that spray foam is so expensive that it can't compete with more affordable forms of insulation.
For more information on this issue, see It’s OK to Skimp On Insulation, Icynene Says.
Thank you Martin. Your answer has more than paid for my subscription to GBA for many years. I suspect the contractor in your article is the same one I spoke with. Appreciate your good work.