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Community and Q&A

How does a bathroom wall assembly dry?

anukeen_sprout | Posted in Energy Efficiency and Durability on

Hello GBA community,

I’m sure this question has been discussed before, but I haven’t been able to find the right search words to find what I’m looking for. If built properly, how does a bathroom wall assembly¬† dry out?

In my case, I am using DensElement on the exterior, which, like Zip, is weather resistant and air-tight. But it could be any assembly that achieves that. On the interior, we’ll have DenShield or other backerboard, and tiles. Probably Kerdi membrane thrown in there too.

This assembly will be nonpermeable on both sides, like I imagine most new bathroom walls are. So where is the wall supposed to dry to…?

Thanks all

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  1. Expert Member


    You want your wall assembly to be able to dry to one or both directions. In your case, although DensElement is air-tight, and works as a WRB, it is permeable, so moisture in the walls can dry to the exterior. Most common wall assemblies, like Plywood or OSB covered by building-paper or house-wrap, work in a similar way.

    Where things become more complicated is when impermeable or very low-perm materials (like some foams), preclude drying to the outside. Then it becomes important to ensure that the interior wall surfaces don't impede drying to the inside. These can be paints, wall-paper, large mirrors, or water-proof bathroom wall finishes. Really resilient walls are often designed to dry to both sides if possible.

  2. Jon_R | | #2

    In your case, you should be most concerned about Summer and AC - in some cases, you should limit the amount of condensation by reducing exterior permeability to 10-20 perms.

  3. anukeen_sprout | | #3

    I love it. Thanks for the input. Happy to report on using this commercial product (DensElement) on my residence after we install it over the next couple weeks.

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