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Rim joist insulation: rigid polyiso, paper fiber backed

gp0901 | Posted in Green Products and Materials on

I have a question regarding insulating my rim joist. I plan on removing the batt insulation and replacing it with rigid foam insulation. A local salvage yard always has foam at a discount price. I called today and they have Polyiso 1 1/2 thick 4×8 sheets for $13.95 ea . I believe it is paper-fiber backed??. They also have 2″ Polyiso foil faced for $22 per sheet. I plan on using the 1 1/2 paper-fiber, stacking it double (total 3″) then sealing the edges with spray foam. Then put the batting back over the cavity. I have some questions.
1. Any issues using the paper-fiber back against the rim joist?
2. Is it over kill to stack (2) 1 1/2″ + batting?
I’m in Michigan which I believe is region 5

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  1. Jon_R | | #1

    > Polyiso 1 1/2 thick 4×8 sheets for $13.95 ea

    Compare to 2" EPS at Menards for $11.56 ea.

  2. gp0901 | | #2

    I think perhaps your quoting 0.5” poly iso at $13.95, not 1.5”. EPS R rating is almost 1/2 compared Poly iso. 2” EPS R 7.7. 1.5” poly R 9.6

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