Construction details for Airtight Drywall Approach and exterior wall shower?
I have a tub/shower located on an exterior wall. We are implementing the Airtight Drywall Approach on the rest of the house.
I haven’t decided between an acrylic shower insert vs. an acrylic tub + tile surround yet.
Would I be running the drywall behind then proceeding with installing the tub using the drywall surface as the construction plane vs using the stud faces normally? Normally you’d install the tub with a flange, shim the walls above the tub out to flush the flange then cement board + wrb + tile.
With inserts you normally secure insert to framing them rock to it (crappy install IMHO as the drywall always swells, pulls away, dissolves, etc over time.)
My concern is the giant gap behind the tub.
Would installing a smart vapor barrier or poly behind the tub in air tight fashion instead of rock and making it air tight with the rest of the air tight drywall work?
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Your instincts are correct. You definitely need a durable air barrier behind your tub/shower. Options include water-resistant drywall with taped seams, cement backerboard with taped seams (and probably a skim coat of joint compound or a liquid-applied waterproofing layer as an airtight layer), or ThermoPly.
For more information on this issue, see:
Air Barriers—Tub, Shower and Fireplace Enclosures
Walls Behind Showers and Tubs
What is an acceptable air barrier behind showers and tubs?