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Community and Q&A

Air-Sealing Foundation Walls

Matteus_Olmedo | Posted in Green Building Techniques on

Hey guys, I’m using continuous drywall to air seal partition/exterior connections and have a step down foundation here that is a little unconventional.  I’m thinking easiest would be to extend the foundation a bit, apply moisture barrier, and then run the continuous drywall above it with a 3/4″ gap between the concrete and the continuous drywall.  Alternatively I could run 1/2″ treated plywood behind and attach the drywall to that.  Any thoughts on the best practice to get an air tight seal while also mitigating potential wicking water damage?

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  1. Expert Member


    I would treat those walls much as you do any basement walls - that is: continuous taped foam covered by drywall.

    The problem is that the chances of your foundation walls being entirely co-planar with the framing above are vanishingly thin, so I would overhang the bottom plate a bit more than the foam thickness, to give you room to shim the lower framing (depending on the drop, probably just a bottom plate), so the drywall ends up plumb.

  2. Matteus_Olmedo | | #2

    Malcolm, I was actually planning on under-slab insulation and the stem wall in question goes down the middle of the house but now that you mention it, probably a good idea to plan for a half inch of exterior foam. Thank you for the advice.

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