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Community and Q&A

Tub with shower surround installation

udLcB6AcF8 | Posted in GBA Pro Help on

I’m in climate zone #5 (Eastern Washington State) and have framed the house with 2×6 walls on 24″centers,OSB sheathing, WRB, 1.5″ foam, 3/4″ furring strips and fiber board horizontal siding. The tub/shower surround is on an exterior wall. Information I’ve seen (JLC Moisture Control, JLC Energy Efficiency and drawings in Strategies & Details) do not show this detail. Without asking specifically about this detail the insulation contractor and bldg dept have indicated that interior poly. is required. I have seen information in the JLC books regarding interior poly/exterior foam and the reference to applicable codes. Given the low energy cost here ( 2cents/kwh) there is little incentive to build different than in the past. I’m looking for information I can take to the Bldg. dept. to get approval for the tub/shower surround install.


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  1. GBA Editor
    Martin Holladay | | #1

    If your exterior rigid foam is either XPS or polyiso, you should be fine. (EPS won't provide the necessary minimum R-value of R-7.5 for your exterior foam layer; for more info, see Calculating the Minimum Thickness of Rigid Foam Sheathing).

    The exterior rigid foam will keep the interior side of your OSB above the dew point, so you don't need interior polyethylene. If your local building department insists that an interior vapor-retarding membrane must be installed, use MemBrain, not polyethylene.

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