Bathroom Vapor Barrier with exterior rigid foam
kramttocs
| Posted in General Questions on
Zone 4 (SW Missouri).
Upstairs bathroom with one exterior wall. 1″ R5 XPS on the exterior with tyvek over that and vinyl siding.
Will be gutting the room and placing R15 rockwool in the cavities after air sealing. I don’t know why but under the current drywall on the exterior wall is 1/4 plywood. There is an exhaust fan/light combo exhausting to the roof.
Add an interior vapor barrier to the exterior wall or leave it off and let the paint handle it?
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Replies
kramttocs,
You may find this discussion useful:
https://www.greenbuildingadvisor.com/question/walls-designed-to-dry-to-the-inside-but-what-about-bathrooms
Thanks for that link. I honestly expected the answer to be no interior poly when there is exterior foam so interesting that Akos mentioned code being both. Hmmm
kramttocs,
When this has one up in other discussions the advice has typically been that small areas, like one bathroom wall, are able to remove moisture by diffusing it into the surrounding framing - and there will be some outward drying as 1" of XPS is over 1 perm.
Many bathrooms also have showers or tubs on the exterior wall, which effusively act as vapour-barriers, so you end up with an impermeable surface anyway.
Adding horizontal 1"x strapping behind the vapour-barrier (an "internal rain-screen") would certainly aid drying.
Thanks a lot Malcolm