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Community and Q&A

Embedded floor joists air sealing

davidmr | Posted in Energy Efficiency and Durability on

I have a 1960’s bungalow in Canada where the 2×10 floor joists have been embedded/cast into the concrete foundation wall. The foundation wall stops about 1″ below the floor sheathing.

I have been considering insulating the rim joist area but because of the embedded joists I don’t feel this is a very good idea because of the potential for the joist ends to rot in winter. It seems the best option is to leave that area un insulated.

What I am wondering is if there is any concerns with just air sealing it? I would do so by filling the 1″ gap at the top with spray foam and then caulking around each joist. would preventing air movement to these embedded portions of the joist also potentially cause moisture to build and rot to form?

Thank you.
P.S. Insulating on the exterior with foam is not an option at this time.

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  1. GBA Editor
    Martin Holladay | | #1

    I think that air sealing work is low risk. Proceed.

    The long-term solution is to cut off the ends of the embedded joints -- the portion of the joists that are embedded in concrete -- and to support the ends of the joists on a new beam supported by columns.

  2. Expert Member
    Dana Dorsett | | #2

    The last time I drove from Vancouver to the Quebec I noticed that Canada is a pretty big place, covering a large range of climate.

    Insulating the foundation walls with embedded joists is much lower or higher risk in some locations than others. Care to be more specific about your location?

  3. davidmr | | #3

    Manitoba, right in the middle.
    -30C winters & +30 summers.

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