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Community and Q&A

Best way to install external polyiso on a timber frame barn

artisanfarms | Posted in Green Building Techniques on

I have a 25X75 timber frame barn with 16′ high sidewalls that I would like to insulate and convert to use as a shop.  I’m thinking of putting recycled polyiso on the outside and skinning the polyiso with metal siding and am looking for ideas on the best way to do this with minimal impact on the inside appearance of the barn. 


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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Andy.

    Is there any framing between posts right now? Are there girts? What's on the barn walls at this point?

    1. artisanfarms | | #2

      There are beams with variable spacing, depending upon their original purpose in the barn, but figure between 4 and 8’ between the horizontal members. The barn is currently sided with vertical tongue and groove wood.

  2. Expert Member
    Peter Engle | | #3

    Powerwash the inside and outside first. Get all of the old stuff off the walls and let them dry. Install black felt paper on the exterior of the barnboard siding. Then install rigid insulation on top of the siding (foam, rockwoll, whatever). Then strapping and siding. You do need to pay attention to air sealing somewhere in the sandwich. Taping the seams in foam insulation can work. If you use rockwool, swap out the black felt paper for peel&stick WRB instead. I prefer the felt paper because it is pretty much invisible when viewed through cracks from the interior. If the siding is in pretty good shape, the color of Blueskin or similar won't be objectionable. This approach leaves the original barnboard visible on the interior and generally untouched, from an aesthetic standpoint.

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