Retrofitting a Vented Cathedral Ceiling
Could this possibly work as an interior retrofit to a 1984 vented cathedral ceiling? To eliminate the effort of removing the existing drywall could I add interior rigid foam over the existing cathedral ceiling drywall in zone 5? I noticed in a previous Q&A about adding rigid foam over existing drywall in a wall application in Zone 5
Martin Holladay responded:
Adding interior rigid foam over the existing drywall is fine. It won’t create moisture issues.
There is no scientific or technical justification for John Clark’s statement that “you could trap moisture within the drywall and generate mold.”
Keith’s suggestion — that “You could have the moisture content of the wall modeled with WUFI” — is unjustified. That would be a waste of money.
So, I was wondering if there was a way to make this work in my cathedral ceiling application, which I realize is a different application
The existing ceiling is 2×8 rafters with plywood roof deck and asphalt shingles. Ventilation is with soffit and ridge venting. It is insulated with R19 pink fiberglass batts which I believe are kraft faced. 1/2″ drywall with a textured finish.
What I would like to add is rigid foam, 1×3 strapping, and 3/4″ thick tongue and groove wood with the intention of making the room more energy efficient
If it could be made to work, would it be better to add additionally a poly barrier on the interior of the rigid foam or not? Is there a type of rigid foam that would work better than another?
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