Closed-cell spray polyurethane foam on 2×8 vaulted ceiling
Long time reader, first time poster…
I am renovating my 1970s house located in upstate NY (Zone 5). The family room has a vaulted ceiling that is framed with 4×8 rafters, 48″ on center. Above the rafters are 2×4 purlins (2×4’s are laid flat), then 5/8″ sheathing and ashpalt shingles.
The ceiling insulation is currently 2 layers of 2″ (4″ total) polyiso. The polyiso is against the bottom of the purlins, leaving a an air gap of 1.5″ (caused by the thickness of the purlins above the rafters). The polyiso has significant damage from rodents. The roof sheathing and shingles are new.
1. Is replacing the interior rigid foam w/ closed cell SPF the only acceptable way to go? (It’s expensive!)
2. Would R-38 (5.5″) closed cell SPF be acceptable? (Code is R-49, but the cost is prohibitive). Building inspector doesn’t seem to care, as I would be far better than current insulation.
3. Do I need I vapor barrier? (I think closed cell is Class II?)
4. Any other ideas? 48″ on center rafters is a bit of a challenge. Also, I’m not keen on furring down the ceiling to gain roof thickness.
The room has a wood stove that is usually burning if the room is in use — I can stomach the heat loss from the difference of R-38 vs R-49 as long as I don’t have moisture issues.
The interior covering of the ceiling will ultimately be 3/4″ pine T&G.
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