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Old 09-27-2011, 11:09 PM   #16
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insulating cathedral ceiling

Originally Posted by ccarlisle View Post
The OP seems to be evaluating the merits of a 'vented' vs an 'unvented' roof and seems to have both options open to most cases, a roof will tend be easier either to vent or not to vent depending on the shape and structure of it. With a vaulted ceiling and knee-walls, he has the option of both.

But in Zone 5a, the question of a vapour retarder comes into it; and for convenience, I'd go with an unvented roof, with 7.5" of closed-cell foam, no baffles - but I'd throw in something the OP perhaps hasn't considered: consider a thermal break i.e. a 2" XPS foam board on the inside. Not only will this meet your R49 code, but will provide that thermal break.

Other options for an unvented roof involve adding something to the exterior of the roof, like XPS or iso-panels, but we're not sure you're needing that.
That will work fine in his location, he hasn't been back for 5 months, good info though, cc. I like your thinking "outside the box".




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