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Is this a sufficient wall system for my basement?

ugsomania | Posted in GBA Pro Help on

Zone 6a. One inch foundation plus type two eps foam adhered directly to concrete with PL. Seams taped and corners spray foamed. 24 oc studs with r20 fibreglass Batts. Should I include a poly vapor barrier before drywall? I’ve been told to omit this as the foundation plus should be sufficient enough for a vapour barrier. Also should I spray foam the small portion of exposed concrete at the top of the wall between the type two foam and the Sill plate? I should also mention it’s an eight foot foundation with about six and a half feet below grade. And there is no foam on the exterior side of the foundation. Thanks for the help.

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  1. mfredericks | | #1

    Hi Mark, I've built a very similar basement wall in the same climate zone.

    It's certainly recommended to omit any plastic vapor barrier over the studs. When adhering the foam to the concrete wall, make sure to use foam board adhesive and not the typical PL Premium. Use PL300 or something else suited for foam board. Spray foaming the top piece of the concrete wall (between the wall foam board and the sill plate) makes sense. Some construction details show a thin strip of foam board ripped down to fill this space with the edges sealed with canned spray foam. The strategy here depends on if you're using cans of foam or hiring a spray foam contractor who could just cover the entire sill plate/rim joist area.

    When I built this type of assembly, I used 1.5" XPS and then built a 2x4 stud wall spaced off the foam to allow me to fit in 2x6 batts, saving some money on framing lumber.
    Good luck!

  2. GBA Editor
    Martin Holladay | | #2

    Your system will work (minus the polyethylene), although I prefer a system that uses only rigid foam, without any fiberglass. For more information, see How to Insulate a Basement Wall.

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