Closed-cell spray foam or polyiso board on rafters under open-cell-foam-filled rafter spaces
This is a follow-on from my recent post:
I could add a perpendicular layer of 2×4’s and spray closed cell foam in the cavity. Or I could use polyiso board over the existing 2×6’s. Either way I have to do some more nailing (or screwing) up there.
I have a couple options for sourcing the polyiso board, I’ve found it locally in 2″ and 250 miles away in 3″ thickness (both recycled). I need to add about R19 so 3″ would be OK. But 4″ might actually cost less in this case.
I’d like to know if anyone here has mounted drywall on a slightly sloped ceiling over 4″ of foam board. Was it worth the hassle? What fasteners did you use?
Or any other wisdom I could benefit from here?
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