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Insulating Rim Joists old Limestone Foundation

alegs3434 | Posted in GBA Pro Help on
I am insulating the rim joists (or band joist/header) on this 1870 limestone foundation house in Ontario Canada. I’m using square pieces of XPS rigid foam with spray foam around the edges. I understand I am supposed to do all of the square cavities shown in blue. My question is, should I also insulate the long parallel pieces shown in red (I think called the sill plate) by PLing foam to it or something? Or only the square cavities that are perpendicular to the joists?
 
 
 
 
 

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Replies

  1. Expert Member
    BILL WICHERS | | #1

    You want to insulate the entirety of the inside surface of the rim joist wherever the exterior surface of the rim joist is exposed to unconditioned outdoor air. That would mean YES, you want to insualte BOTH of the areas you mentioned, assuming the other side of those walls is outdoors.

    My preference here would be to use EPS foam instead of XPS too, which will probably also be a little cheaper. EPS allows for a small amount of drying ability, which is a plus here.

    Bill

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