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Community and Q&A

Rim joist insulation

GarrettWatson | Posted in General Questions on

Live in Canada, winters are cold. Last couple of years we have noticed frost build up on the baseboards in a couple of spots and now I know the problem, but don’t know the fix and I am looking for ideas.

Basically, we have a double rim joist half filled with concrete and one lonely piece of fiberglass pink insulation in between. Needless to say there are some big cold spots upstairs. See my detail attached, wondering if anyone has some good ideas to deal with this that do not involve ripping off rim joists :).

Thought drilling some holes from the exterior and blowing in dense pack might be the best solution?

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  1. Expert Member
    NICK KEENAN | | #1

    I would look into slow rise closed cell foam. Check out this page:

    In particular, watch the video. The foam is sprayed into closed cavities through a 1" hole using a 7/16" tube. In another video they show taping clothes hanger wire to the tube to give more control over aiming it, I would think of using an electrician's snake for better control.

    I don't know, but my intuition is that the existing fiberglass won't give any problems, I think the foam will just push it out of the way. It may be an obstacle to the foam wand though. There is a service called RetroFoam that is specifically marketed as foam meant to be pumped into cavities where there is fiberglass; I know nothing about their quality or effectiveness.

    I think the hardest part would be figuring out when you've pumped enough in. I would calculate the volume of the cavity and the weight needed of foam to fill it, and then put the tanks on a scale as you spray.

    1. GarrettWatson | | #2

      Thanks. I didnt know slow rise foam was a thing. Will definitely check that out as an option.

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