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Bathroom remodeling & insulation

emmsvsnvk | Posted in Building Code Questions on

Two questions on insulating exterior wall of tub/shower area. I am in northern Pennsylvania.
Currenlty the wall has hardboard siding and sheathing that is not vapor resistant, the rest is stripped down to the studs. I plan on adding fiberglass, then 6-mil poly, then cement board, and tile.

Is this method appropriate for the area i live in?

Second, there is a small area on this wall that was patched to shorten a window. This area is 2×2 ft. The sheathing is a foil backed foam board. vapor resistant. Is it acceptable to add fiberglass and poly before the cement board and tile for this area?

The layers, from out to in, are: hardboard siding, sheathing, studs and fiberglass, poly 6-mil, cement board and tile. (Only difference is in the patch area)

Or does anybody have a better recommendation?

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  1. GBA Editor
    Martin Holladay | | #1

    In your area, interior 6-mil polyethylene is not recommended. I would skip the poly, since poly can interfere with the wall drying to the interior during the summer.

    Almost any type of wall insulation would be better than fiberglass batts. Closed-cell spray polyurethane foam will perform better in this application, although it costs a lot more the fiberglass batts.

    Whatever approach you take, be sure to pay attention to airtight construction techniques. Airtightness is much more important than whether or not you include a 6-mil vapor barrier.

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