How can I best retrofit and insulate an existing cathedral ceiling?
Thanks for this excellent blog. I have a 22 year old home with a “great room” and cathedral ceiling. From inside it is v-groove pine, probably no taped sheetrock beneath but I wasn’t around when it was built, and 12 inch fiberglass with kraft paper. (It has the built up/down rafters you have mentioned). There is a vented area above fiberglass, probably about an inch and a half (soffit and roof vents; there are a couple of dormers). One can see ice and icecles on the roof, and the place takes alot of wood (and propane) to heat. Oh, I’m in northern Vermont, zone 6.
The original roof will need replaced in next few years so a good time to consider improvements. If done from above, I know you (Martin) prefer poly foam. This can easily be blown into the bays once decking is removed. Can that be blown right over kraft paper once fiberglass removed? (if only to keep uncured foam from squeezing through board seems and knots). Can we do a few inches of foam, due to cost, and then reuse the fiberglass batts above? Can those batts be compressed a bit to fill up the remaining cavity and thus reach the underside of the sheathing?
If so, what then? The venting would of course then be closed off, so what about above the decking? You seem more comfortable with a venting area, although it would be simpler if none were needed at that point). But can we go with no further insulation? I can see the benefit of more rigid foam above, but am surprised at how much (and how much expense) is still needed above, not to metion the challenging furring issues above xps to move to wood for roof attachment.
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