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Basement spray foam insulation over weeping tile?

an123 | Posted in General Questions on

Question probably for Martin:
My 1930’s house is in zone 4 (NS), has a full uninsulated concrete foundation.  After years of research, I’ve decided to spray foam the basement walls (up into the rim joists) with Demilec closed cell spray, to be covered with sprayed-on cement (cementious?) thermal barrier.  Previous owner installed weeping tile, dimple mat (3-4 inches up) the inside perimeter foundation walls (however there is no sump pump etc.). I’m not sure why it was installed, I haven’t seen water issues in the 8 years I’ve lived here.  The weeping tile may also be causing some basement radon that I would like to reduce (200-300 units).  So, I was thinking of having spray foam sprayed down to the floor, over top of the weeping tile.  I see in your feb.’21 article that you suggested to put a sill sealer between the spray foam and floor as well.  Will there be any issues to spraying over the weeping tile (re having the back of the foam exposed to moist air from under house)?  Re another moisture issue – the rim joists, I don’t think there is a sill sealer between them and the foundation.   Thanks for your thoughts.

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  1. Expert Member
    NICK KEENAN | | #1

    Photograph 13 in this article shows something similar, I think:

    If it's good enough for Lstiburek it's good enough for me.

  2. Expert Member
    Joshua Salinger | | #2

    The closed cell foam should stop any water vapor from the soils driving to the interior of the basement. If there is a bulk water issue, that is a different story and I wouldn't rely on the ccsf to take care of it. So long as you have never experienced any water intrusion in 8 years and the basics are done right (gutters, downspouts, sloping soil away from the house, etc) you have done the best you can shy of excavating the outside of the basement walls and treating it from the exterior. If the weeping tile (I'm assuming french drain) runs to a sump or daylights then it is doing its job and keeping hydrostatic pressure from the ground from coming up into your basement during water events. If the top of the weeping tile is covered with the ccsf I don't see how this would hurt anything. I would cover the weeping tile with a membrane before spraying the foam so it doesn't clog the holes in the tile. I hope I am understanding the question correctly...

    In regards to the lack of sill seal at the rim joists, depending on the age of the house, it isn't uncommon to see no sill seal in older buildings. This isn't great, but it also isn't weird in the sense that it was typical construction back in the day. If you aren't seeing water damage or rot then it is likely OK.

  3. Expert Member
    BILL WICHERS | | #3

    If water comes through the foundation, it will cause the spray foam to lift. If the dimple mat can "catch" all of that water though, you should be OK. The problem with putting anything on the inside face of a wall with water on the other side is that if the water makes it's way through, it will act to push the sealer off of the wall. This same thing happens with products like Drylok (and they warn you about it on the package).

    Spray foam is a common way to seal up and insulate rim joist areas though. As Josh mentioned, sill seal gaskets are a relatively recent addition to building codes. Back in the day, you usually had none, or maybe some asphaltic fiberboard was used to keep the wood from resting right on the foundation. Either way, you'll probably have some air leaks without the gasket so I'd consider spray foam for this area.


  4. an123 | | #4

    Thanks for your responses and advice. I did end up spray-foaming with closed cell spray. Unfortunately it did not decrease my radon issue and I am now in the process of getting radon mitigation quotes.

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