I am about to pull a failed insulation attempt (4″rigid foil faced polyiso “cut and cobbled” in rafter bays) in an un-vented shed roof. Doing so seems to be the best bet rather than gamble on moisture problems down the road. Luckily I have not sheathed the interior walls yet so the process could be worse. There has been plenty of ink spilled on the topic here, but I just want to get it right this time!
So, my best bet -and possibly cheapest option- is to hire a professional to spray 7″ of closed cell foam into the 2×8 rafters and call it a day. Mind you, I am grandfathered out of meeting R-38, though this will be close. Any additional tips for this unvented ceiling arrangement?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part