Does adding 2″ polyiso to the interior of an unvented cathedral roof assembly cause any problems?
I am building a new home with cathedral ceilings in a cold climate (zone 6) and have a question about the roof assembly. The plans from the architect call for a 2×12 rafter furred with ripped 2×6, giving a rafter depth of about 14″. My builder is uncomfortable with the connection of the furred 2×3 to the rafter and has suggested an alternative. He has proposed skipping the furred strip and just go with the 2×12 rafter and then use 2″ foam and apply that to the inside of the rafter. The foam could be installed before the cellulose and then the cellulose could be pumped in behind it. Might make for an easier job installing the cellulose. I have seen lots of unvented cathedral roof assemblies with foam on the exterior but none with it on the interior. Does this sound like a good plan?
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