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Air sealing old flooring

ctaircooled | Posted in General Questions on

A portion of the first floor of our house has old pine flooring (no subfloor) with a lot of gaps and cracks that I suspect is a significant contributor to the draftiness of the house.  Any recommendations on how to approach this?  My thoughts were add 1/4” foam board inside each cavity.

 This portion of the house is from 1890, has stone foundation and a drafty sill plate that I plan to insulate with spray foam next summer.  The house was renovated in the 80s so has updated windows and fiberglass insulation in the walls but it is still a chilly house!

I appreciate any help or insight. Thanks.


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  1. 1869farmhouse | | #1

    What’s below this floor? Unconditioned crawl space?

    If so, you might be better off encapsulating the crawl space and kill two birds with one stone.

  2. Expert Member
    BILL WICHERS | | #2

    If you’re just looking for a temporary air barrier until next year when you’re planning to insulate/encapsulate your crawl space, then I’d tack some housewrap up under the joists with a staple gun. Tape the seams, and seal the perimeter as best as you can to whatever is available. Be careful that you don’t have a leaky rim joist leaking into your now semi-sealed floor.

    Note that this would only be a temporary air seal, I would not rely on it long term, and I would consider it only to be “better than before” and not really “sealed”.


  3. ctaircooled | | #3

    It’s a full basement below. Once sill plate is sealed is the floor not a concern as is? I assumed both needed to be addressed.

    1. Expert Member
      NICK KEENAN | | #4

      Eventually you will need to decide if the basement is inside or outside the conditioned part of the house. In old houses this isn't really a concept they had, basements and crawlspaces were kinda inside and and kinda outside. If the basement is inside it should be sealed and insulated. If the basement is outside the floor is the barrier and it basically should be sealed and insulated like an exterior wall.

      1. ctaircooled | | #5

        That makes sense. Thanks.

    2. Expert Member
      BILL WICHERS | | #6

      You generally don’t need to seal the floor if the basement is part of the conditioned space. This means you want to seal your rim joist, and ideally also insulate the rim joist and basement walls. If you do that, there is no need to seal the floor.

      My recommendation would be to seal the rim joist if you haven’t already done that, make sure it’s insulated properly (lots of info on this site about how to do that), and then insulate the basement walls (lots of info here for that too). You’ll get a pretty Big Bang for the buck just sealing and insulating the rim joist, so if you want to spread this project out that is a good first step. It’s easy to come back and insulate the rest of the walls later.


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