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Do you need poly behind tongue & groove pine boards?

DianeGraff | Posted in General Questions on

We live in Iowa in a log home.  We are finishing the upstairs loft area with pine tongue & groove boards.  We have a type of space age aluminum foil insulation on all the walls and ceiling.  Do we need any type of poly or anything behind the wood we are installing?  We are not installing drywall but wondered if we need any other type of poly?   Thanks

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  1. Expert Member
    Dana Dorsett | | #1

    That "...space age aluminum foil..." is buying you roughly zero in additional thermal performance when in contact with the adjacent layer, and only a modest amount with air gaps on both sides. But foil is a vapor barrier at least as vapor-tight as 6 mil poly, so there's no point to adding a layer of polyethylene. The foil can be made relatively air tight too, with the appropriate tapes.

    Before finishing off the room it's probably worth installing some REAL insulation of some type though.

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