Insulating back of attic-exposed shower

schilcurFebruary 27, 2014

To All, much to our dismay the unseasonably cold weather in TN exposed a weakness in an upstairs bathroom. We came home one night to a rain storm in the kitchen. Turns out the back of the fiberglass shower in the bathroom is completely exposed to the attic. The cold air simply followed the open space under the shower and froze the cold supply pipe. The pipe has been fixed, we're getting estimates to remodel the kitchen but I still need to fix the root cause. I try to be as much of a DIYer as possible. I was think about blocking the cold air using spray polyurethane foam and closing off the back of the shower with a piece of exterior sheet insulation. I was quite surprised that a contractor would've left the shower exposed like that. Any comments/suggestions about my forward?
Thanks in advance, Curtis

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mongoct

You can close off the back of the shower with rigid foam board insulation, but you need to properly detail that cavity with regards to the rest of the house's thermal envelope.

ie, if you simply fasten RFBI to the back of the shower, you've protected the plumbing from cold air from behind. But what about the top? Or the floor, through the joist bay?

I wouldn't encase the plumbing behind the shower wall in spray foam. I'd prefer that warm air be allowed to pass through the fiberglass wall, warm the plumbing cavity, and keep the pipes warm that way. By properly detailing the back cavity (back, top, bottom, sides, etc) that encloses the plumbing, the plumbing cavity will essentially be a part of the heated part of the house.

I hope that makes sense.

    Bookmark   February 28, 2014 at 4:42PM
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schilcur

Thanks for the input. Bottom/top/sides of the shower are all enclosed as part of the original construction. Just the back side (opposite wall from showerhead) is exposed to the attic. I was thinking along the same lines as you, rigid foam board across the back and caulk it to seal out the cold air and go from there.

    Bookmark   March 3, 2014 at 8:23AM
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