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Should a plastic 4mil barrier be used?


Mark P
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House is maybe 50 years old, wood panel exterior siding, 2x4 framed exterior walls. A new shower surround is being installed against an exterior wall. Fiberglass batt insulation will be installed in the wall cavity with kraft paper facing the inside of the house and the new surround placed over that. Should a 4mil plastic barrier be placed over the studs behind the shower?

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It would be a pre-fab fiberglass. I don't know how many pieces. The question came up with some people I know who are refabing a house. One of them saw on HGTV that a plastic barrier is needed between the shower and outside wall or else there would be a mold problem. There has been some discussion and some think the plastic would cause more of a problem, some think the kraft paper would be fine.

Why would you use a cement backer board?

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It'll absorb vapor diffision and release it slowly. Otherwise, you might end up with rivulets on the plastic barrier. With no way to drain that 4 mil into the shower pan you wouldn't want that.

Did you consider closed-cell foam with a barrier for that exterior wall? Fiberglass doesn't provide the most consistent wall you know.

OT - OF!!!

M.

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I'd never use the polyethylene sheet for reasons Mike said.

I'm somewhat confused why anyone thinks they want or need a sheet there; isn't the plastic shower wall a vapor barrier?

Honestly, this is something I really don't know. I never see plastic shower surrounds; maybe a dozen my entire career. All I see is tile surrounds, and that's another story.

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House is maybe 50 years old, wood panel exterior siding, 2x4 framed exterior walls. A new shower surround is being installed against an exterior wall. Fiberglass batt insulation will be installed in the wall cavity with kraft paper facing the inside of the house and the new surround placed over that. Should a 4mil plastic barrier be placed over the studs behind the shower?

Either green sheetrock or cement board should be over the studs, plastic not needed.

Most of the plastic (fiberglass) surrounds have no body and they need to be against a solid surface. Think of an adult slipping and bumping one without support and popping one of the interlocking seams. P.S. I hope the water supply is on the interior wall and not the exterior.

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