I live in the Pacific NorthWest in what I believe is a zone 4 marine environment. Our house was built in 1979 and is in decent but outdated shape. I'm remodeling a 5'x7'bathroom and have removed the sheetrock on the one exterior wall to reroute some plumbing. When I removed the original sheetrock I also removed the insulation which had a soft almost flour like texture that would pretty much crumble in my hands.There was no vapor barrier on the interior, and as far as I can tell there is no vapor barrier on the exterior.
I'm now getting ready to close up the wall and have two questions.
- When I insulate this exterior wall using mineral wool, will I need to put up some kind of vapor barrier? if so what do you recommend?
- Part of this exterior wall will be used by the shower/tub. The shower surround I'm using is Flexstone over cement board, will I need to use a vapor barrier on that area as well? If so where would it go, over the insulation before I put the cement board on?
Best Answer
In the Pacific Northwest you do want an exterior vapor barrier we get enough wind driven rain that this is a big deal. The original insulation sounds like a cellulose type, I have never used on new construction, by 79 fiberglass was the common type for new construction in this area. I have always used heavy plastic behind my backer so I don’t have any experience with flexstone. as I have always used a membrane behind backer because I don’t want the constant moisture that can penetrate grout and backer or even tile depending on the type a non permeable surface there but still a vapor barrier on the exterior wall. Try to overlap and make sure to go up to the eves so water can not easily get behind it and damage the sheathing.