Insulating between shower wall and exterior brick wallexteriror block [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

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MGotcha
11-16-2010, 01:47 PM
I am installing a new shower against two exterior walls of a cinder block home, and wish to add some insulation within the 1.5" furred out space between the exterior block wall and the shower walls with something like 1.5" "R-Tech" solid foam sheeting. Shower walls will be 1/2" wonderboard mounted on the furring strips, redgard & then tile. Will the foam act as a vapor barrior, which would cause problems since the redgard barrior is on the opposing side of the wonderboard or would this be OK?

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bbcamp
11-16-2010, 02:15 PM
While the perm rating for this material disqualifies it as a vapor barrier, it will be a vapor retarder, so yes, technically, you'd be making a moisture sandwich. I think you'd be OK with a couple of changes: Either lose the furring strips, or change them to metal and use a non-fiber cement type board so you don't have any organic material between the moisture barriers. You could use tapcons and fasten the backerboard through the foam into the concrete.