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Another shower in basement insulation question

pc80 | Posted in General Questions on


I am currently renovating a previously half finished basement, replacing all the drywall and adding a new bath/shower room. The previous set up was drywall, then poly, then fibreglass batts in the 2×4 frame, then a small gap (<1/4″) to the concrete basement wall. There was no signs of any moisture or mould when I took everything apart. 

The question I have is how to insulate for the new shower room given there will be much higher moisture produced now. My thoughts are I would ideally go with foam board, then reuse the old fibreglass batts, then a smart vapour barrier before drywall, however this would mean removing the existing frame to make space for the foam board (which I’d rather avoid as this will add a lot of work). Will be using kerdiboard for the shower panels. Would another option be to just put house wrap behind the framing instead of the foam board? With this the house wrap would likely be in contact with both the concrete and batts. Would I seal/glue the bottom of the house wrap to the base of the wall and staple to the back of the frame? 

My second question is that the concrete does not go the full wall height. There is a 2 ft pony wall which results in a space at the top of the wall behind the frame. At the back of this there is another layer of drywall, poly and insulation. Should I remove this, and what would be the best option to fill this? Remove the poly as the smart barrier will now be there, caulk any gaps and fill it with fibreglass?

Home is in Alberta, build 1970. A very dry climate with cold winters. 

Thanks in advance


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  1. Expert Member


    It's always hard to give advice for projects in Alberta because you can get away with things that would fail in most other climates.

    Your existing set up would have moisture problems here and most other places. The question is can you rely on that climate advantage, and a bit more air-sealing, to stop the increased moisture load from reaching those cold concrete walls? The only way to know would be to do it and take the consequences if it fails. My best guess is you have high enough chance of problems developing that I wouldn't risk it. Your other option if you don't want to re-frame is closed cell spray foam.

    For the framed pony wall you have two choices. You can leave everything as it is and not add insulation to the new inner wall, or if you want to add more insulation, the existing drywall and (importantly) the poly needs to go, as otherwise it will be too far towards the exterior.

  2. 5Stud | | #2

    I would definitely remove the framing and move it to 7 inches and get R20 ish.
    The pony wall as Malcolm said, remove drywall and poly.
    I like to bump 1.5 niches from the vapour barrier to an exterior bathroom wall.
    While the basement is open you should run a bead of some flexible polyurethane caulk on slab to wall joint.

  3. pc80 | | #3

    Thanks for the advice. Appreciated. Do you think the smart barrier on the areas away from the shower is still worthwhile?


    1. 5Stud | | #4

      Probably not a popular answer on GBA but
      Poly works in your climate zone just fine!

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