In zone 4A, would I be OK to put 1.5″ of closed SPF under my roof deck with unfaced R-38 below that?
I have 2×8 rafters, and they are furred down with 2×4’s and there is a 1″ gap as a thermal break between them. I want to foam the rafters entirely as well as the underside of the roof deck. I would use .5″ sheetrock as an air and thermal barrier below the furring and batt insulation. I know code calls for R-15 air-impermeable foam, but with this set-up in southern, coastal Virginia would this be OK?
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