Bathroom Shower Exterior Wall – Vapor Barrier or Not?
scottwoodward
| Posted in General Questions on
I’m in climate zone 5 with 2″ exterior polyiso at R13.5 and R21 Rockwool in the wall cavities. One of my shower walls is on a exterior wall. I’m planning to waterproof the cement backer board for the shower tile, but I see that a vapor barrier is usually put on top of the insulation, being the cement board.
What’s the best/right answer for my situation? Skip the vapor barrier for that one wall or is it needed?
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Replies
Probably not worry about it too much since it's a small area of a larger assembly. Many shower waterproofing products are vapor closed and you end up with this situation. A good assembly on each side means there's no vapor getting inside those cavities. An incidental small amount that does should be able to migrate laterally and dry.
Vapor retarders/barriers are extra-important with shower walls, since there is zero ability to dry to the interior, you really don't want any moisture getting into those walls.
When you say "skip the vapor barrier for that one wall," does that imply you are using a VB in the rest of the assembly?
No. Sorry for the confusion in the way I worded the question. I'm not using a VB anywhere in the wall assembly.