Tub/Shower Surround on Exterior Wall
We are about to start a new construction project. For one of the planned bathrooms, we’re really stuck with the tub/shower surround against an exterior wall. I’d like to know if this is considered inherently risky from the perspective of the wall being able to dry and, if so, what steps can I take to mitigate the risk.
On the interior, the wall in question is the long wall of a 3×5 tub/shower surround. Plan is to use Schluter KERDI and porcelain tile to finish the surround.
On the exterior, wall will be from outside in: fiber cement siding; rainscreen gap; felt paper WRB; foil-faced Rmax polyiso (taped) for continuous insulation; sheathing nailed directly to 2×6 studs; blown-in fiberglass cavity insulation. I know technically it would be possible to detail the foil-faced polyiso as a WRB, but my GC prefers to use felt paper for that and I kind of like the idea of the polyiso being a backup here.
Does the foil-faced polyiso on one side and the KERDI+tile on the other side create a dangerous vapor impermeable sandwich? Should I be considering other details?
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