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Vapor barrier in bathroom


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Doing a bathroom remodel, so I cut up and took out the existing shower/tub surround. On the exterior wall there wasn't plastic behind the shower portion. Plastic came down about two feet then where the shower portion was there isn't any plastic. Is this normal or should there be plastic covering the insulation all the way down? Built in 1987 with siding, foam board insulation, "tyvek", then fiberglass insulation if that makes a difference.

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I am not sure if ND uses the IRC codes, if they do, section R318.1 states:

In all framed walls, floors and roof/ceilings comprising elements of the building thermal envelope, a vapor retarder shall be installed on the warm in-winter side of the insulation.


1. In construction where moisture or freezing will not damage the materials

2.Where the framed cavity or space is ventilated to allow moisture to escape.

3. In counties identified as in climate zones 1 through 4

I would suggest that you make the vapor barrier cover the whole back side of the tub and surround, from floor to ceiling.

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The best thing you could do from an air tightness standpoint is to insulate/vb and drywall the backwall completely, then install the tub and then drywall around the tub, which would be a second layer above the back wall..

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Understand there is a difference between a vapor barrier and a vapor retarder. Also know that you need a air barrier covering insulation.

A vapor retarder would be painted drywall.

At a minimum there should be insulation with drywall. Do you know how thick the foam is. That can make a difference in how you might handle the wall.

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