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Rim joist insulation confusion

GarrettWatson | Posted in Green Building Techniques on

I am in the process of renovating my basement and will be adding insulation to the exterior walls.

This was a finished basement and very warm in winter. Problem though was on the main floor where we had frost build up due to poorly insulated rim joist cavity. Lots of frost when I took down the pink stuff and it wasn’t even that cold yet (-10 celcius).

Anyway, I am going to put back 2″ rigid board on the walls then frame with 2×4 and then batt inside there with a smart barrier on top of that.

My confusion is on the rim joist. Everything I have read has indicated put the rigid board against the rim joist and seal, then add batt to fill the cavity.

My confusion is from the NRCAN (Natural Resources Canada) website which shows the opposite, batt against the rim joist then a final piece of rigid board insulation against that then the drywall

So which one is it? Or do they both work?

I live in a climate with winter temps reaching as low as -35 degrees celcius (lucky me).

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Garrett,

    I'm not sure why that detail is shown with the fluffy insulation installed first, but more commonly the rigid foam would go in first and be sealed in place with canned spray foam or caulk, then you can fill out to the plane of your drywall with any other insulation material that you would like.

  2. Expert Member
    Dana Dorsett | | #2

    This is Building Science Corp's best-practices recommendation:

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