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Community and Q&A

Managing moisture in exterior shower wall

mrkawfey | Posted in Energy Efficiency and Durability on

I am still working through all the details of our renovation project and, while I am happy with our planned wall assembly, there is one area that I could use some input.

In the master bath, one of the tiled walls for the shower stall will be on an exterior wall. As mentioned in my previous posts, our exterior walls have 1″ of foil faced rigid polyiso and can’t dry to the exterior. I am concerned about tiling and sealing this wall completely from the interior as it will not allow any breathing inward. Additionally, because it is in a wet environment, there is always the chance that, despite best efforts, water could get in. 

Does anyone recommend venting this wall? Maybe drilling holes in the top plate and bottom plate to allow it to breath to the vented attic? Are there other methods I should consider?  Since we will be opening it from the inside, all options are on the table. Unfortunately, moving the shower is the one option that would be a last resort. 

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  1. Jon_R | | #1

    Can you provide some ability for air/vapor to move to areas that aren't tiled (ie, have some inward drying)?

    1. mrkawfey | | #2

      In what way? I suppose I could allow the individual stud bays to be open to each other internally until it reaches one on each end of the tiled wall that is simply drywalled.

      That could be done by drilling a few holes in each stud at different heights. I have no idea how much open area would be needed.

      I suppose another option would be a thin service cavity that provides an air gap between the exterior wall and the tiled wall and then connects to the interior wall at the corner.

      1. Jon_R | | #3

        Exactly. Not clear how much air movement is needed - I expect very little.

  2. Expert Member
    Akos | | #4

    I'm in the land of exterior rigid insulation and interior poly. No problems with showers. Make sure you air seal, this is always a much larger source of moisture in walls than anything else.

    I also recommend one of the decoupling membrane products for showers. With proper detailing, they guarantee a water tight assembly, and can be installed over standard drywall.

    If you are building something like a steam shower, I would go with SPF in the walls.

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