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Air-Sealing an Insulated-Slab Perimeter

lenny_meyer | Posted in Energy Efficiency and Durability on

Apologies if this question has been asked before on GBA (I’m sure it has), but I’ve had trouble following some of the more technical answers.

I’m trying to learn, in layman’s terms, how can I air seal the perimeter of my poured concrete foundation slab.  There is Roxul insulation around the perimeter (see attached photo).  There is also Roxul underneath the slab with polyplastic over that.  The plastic was taped up onto the foundation walls, but no one besides the concrete contractor was on site at the time the slab was poured.  Being unfamiliar with this process, the contractors cut it off 🙁

The builder that was hired to construct the “weather tight shell” assured me after this mistake that there was a “plan b.”  Unfortunately, we’re no longer able to work together (because of lots of neglected details like this — some much more serious).  So it is up to me now to get this home air, water and weather tight, and I never knew what that plan b actually was.

Can anyone advise on the simplest, yet effective way to achieve air sealing the foundation slab at the perimeter?  Or if there is a good youtube video you can link to, that works as well.

Thanks so much!

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  1. GBA Editor
    Kiley Jacques | | #1

    Hi Lenny,

    I'm giving your question a bump. I found this video by Matt Risinger: Perhaps it will be helpful in your situation--which, by the way, is such a bummer! You have my empathy.

    1. lenny_meyer | | #4

      Thanks, Kiley. A bummer indeed! Some windows and doors need to be reinstalled...what a hassle and expense!

      That video is great. Since my original post I've had a blower door test which shows the seal between the concrete and sill plates is pretty good and tight, so nothing to be done there. I'm still trying to figure out the slab to wall seal though!

  2. Expert Member


    How are you planning to insulate the foundation walls? If you are planning on using foam it will be sealed around the perimeter, which will take care of the slab.

    1. lenny_meyer | | #3

      Hi Malcolm, thanks for the reply. The foundation walls are insulated on the exterior with Roxul already, so I suppose foam isn't going to help me.

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