Hydro ban board/Vapor Barrier
While I'm installing Exterior Wall with the framing 8" (New build). Should there be a vapor barrier behind the hydroban Board? I have r-21 faced batts in the stud bays. Where the reccessed niche is in the exterior wall, I have 3-4" of available space for either foam board installation or batts. I'll get more r-value with foam board insulation but my concern is the orientation of vapor barrier.
Closed cell foam board with a foil face facing inside with hydroban board on top is good or bad? I'm assuming Rockwool would be safer but this will shrink the niche sill by 1" do to the thickness.
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Apologie accepted.
I would still build normally with plastic vapor barrier and insulation. Because here's your wrench. Hydroban has that vapor coating on BOTH sides. So are you using 3 vapor barriers? No. Not really.
The vapor and water intrusion properties of hydroban board is related to your shower \steam room. And not so much the envelope of your home. It's stopping all that shower moisture from getting behind it. not really a thermal thing.
I've used rockwool and that 2" rigid foam together before in the same place. We peeled off that tiny foil layer on the foam and went plastic over the whole thing for the reasons you are here now