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"effective" R-value for spray foam insulation?

2458 Views 1 Reply 2 Participants Last post by  PaliBob

I've been in contact with some contractors for spray foam insulation for the underside of a new construction roof. Although they say the foam has an R-value of 7 per inch, they say the 'effective' R-value is double that because there is no air movement within the material. Thus, I don't need 7+ inches to get R50, I'll only need 3.5-4 inches. Is this true?
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Don't ask for ''inches of foam" ask for "R50".

Run this by your architect and local building permit office.

If the contractor signs up for R50, then there are legal issues if R50 is not installed.
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