Mitigating moisture at wood finished vaulted ceiling
Construction_Paper_Studio
| Posted in GBA Pro Help on
Hello Everyone!
I’m renovating a room with a vaulted ceiling whose final finish is walnut plywood. This home is in Oregon. On the interior side of the insulation/framing, I’m installing a layer of MemBrain vapor retarder. Then comes the plywood!
I’m wondering if I should finish/stain the plywood in a way that limits its permeability or if I should allow it to breath as much as possible. Please see the section detail. Am I at risk on condensation forming between the MemBrain and the ply? Thoughts? Any insight is super appreciated while navigating the tricky world of building science!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
In theory your stackup should work well. In practice, some people have experienced moisture concentrating and eventually condensing at the ridge, sometimes enough to drip from the ceiling. This seems to be especially the case when there is a heavy ridge beam extending from inside to outside and creating something of a thermal short. I generally try to minimize this behavior by making a small flat at the underside of the ridge so that I can put a few inches of insulation under the ridge beam. Other than this possibility I wouldn't worry too much about moisture condensing between the Membrain and the plywood. Any finish should work. If the Membrane is your air sealing layer as well as the vapor retarder, make sure it is as airtight as possible.
Someone can correct me if I'm wrong, but I believe code says ceilings and walls must be covered with a fire resistant sheathing(i.e. drywall). Then one can apply whatever they like.