A contractor on a job in Mill Woods said he never uses a moisture barrier behind shower tile in our climate

I was helping a friend with their bathroom demo last week, and the tile guy they hired made a point about Edmonton's dry air. He argued that with our low humidity, especially in winter, a plastic sheet or waterproof membrane behind the backer board can trap the little moisture that does get through and cause mold inside the wall. He just uses a cement board with sealed seams and proper grout. But I've always read and been told that a barrier is a must-do, non-negotiable step to protect the studs. It got me thinking about whether standard building advice always fits our specific prairie conditions. Has anyone else run into this debate or have experience with a shower built without a traditional moisture barrier holding up over a few Edmonton winters?

3 comments

3 Comments

clark.robin1mo ago

Whoa, that's wild. My old plumber said the exact same thing about trapped moisture here. He swore by just using the cement board right.

simon7171mo ago

Yeah, the "trapped moisture" thing is exactly what got me. I used to think putting something behind the cement board was always better. But then I saw a bathroom where they did that and the wall was wrecked a few years later. Now I'm totally with your plumber, just board right on the studs and let it breathe.

kim_west29d ago

Ask your plumber if he's ever seen what happens when you put foam insulation right against the exterior sheathing behind a shower. I'm curious if the same logic applies there. I've heard guys online argue that the foam traps moisture against the studs too, but then others say it's fine because it's closed cell and doesn't absorb water. Seems like nobody can agree on anything related to building science anymore haha. What's the climate like where you're living? Around here it's humid as hell, so any kind of sealed vapor barrier feels like a ticking time bomb.