Cathedral ceiling: vented or unvented?
The previous owner of my home built a cathedral ceiling with skylights in the attached family room. I recently had a chimney removed from this room and it became apparent that the space between the ceiling and the roof sheathing is totally un-vented. The ceiling is finished with stained pine and I’d rather not have to take it apart (I believe that there is drywall underneath the wood).Also, when it is really hot in the summertime, the room smells like an attic, which is probably explained by the lack of venting.
I was do for a new roof before the chimney removal and definitely need one after. Initially, I was thinking that I would have the roofer remove the sheathing (it’s probably not in good shape anyway due to lack of venting), and lay down some fiberglass between the rafter bays, cover with rafter chutes, re-sheath, and install a ridge and soffit vents. However, the contractor who worked on repairs after the chimney demolition noted that my rafters are only 2x6s and that there probably won’t be enough room for insulation AND venting. On the other hand, the pitch of the ceiling looks like it’s not as high as the roof pitch, so there may be plenty of space near the ridge, just not so much near the soffits.
The contractor suggested sticking with an unvented roof, but that I should instead have the top side of the ceiling spray-foamed from the outside before re-sheathing. Obviously, this would only work if there is drywall behind the tongue-and-groove wood ceiling. It kind of makes sense to me since it blocks water vapor from making contact with the roof sheathing AND seals the interior space off from the air in the void between the ceiling and the roof. However, this is not how un-vented cathedral ceilings are usually built. Everything I have read about this says that the roof deck itself should be foamed, but in my case, that would require taking the ceiling apart.
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