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Community and Q&A

Insulating walls (pole barn)

JohnS2 | Posted in General Questions on

I’m going to insulate part of my 36’x48’ pole barn for use as a living space. My plan is to put 1-1/2” Foamular between the 2×6 girts (against metal siding). Then place an additional layer of 1-1/2” layer of Foamular on the inside of the grits (over first layer). This layer would be sealed with tape and sealant. I would then fill the remaining space with 3-1/2” Fiberglass insulation batts. This would be covered by Sheetrock. Do you see any issues with this approach?

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  1. Expert Member
    Dana Dorsett | | #1

    A couple of issues.

    1> Foamular is XPS, which is blown with climate damaging HFC blowing agents.

    2>Even though it is labeled R5/inch, it's only warranteed to R4.5/inch (90% of labeled R), and over several decades it decays to about R4.2/inch, the same as EPS of similar density. (EPS is blown with pentane, a much lower environmental impact agent, most of which escapes the foam and is recaptured at the manufacturing facility.)

    Using 1.5" polyisocyanurate ( also blown with low impact hydrocarbons) would deliver a somewhat higher labeled R and higher lifetime R. It's much greener stuff, and usually costs less per labeled R than XPS.

    Using RECLAIMED foam board (any type) is greener still, since no new polymer or blowing agent is used. Re-use just piles on to the benefit side of the environmental cost/ benefit balance. It's also usually less than 1/3 the cost of virgin stock foam.

    With only 1.5" XPS (about R6.5 over the long haul) on the exterior of the 2x6 girts and R13 on the inerior side the girts may get cold enough to collect excessive moisture over a winter in US climate zone 6 or colder, but will be fine in zone 5 or lower.

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