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Do I need a poly barrier between concrete and 3″ poly iso foam?

John Waller | Posted in Energy Efficiency and Durability on

I have an 8″ exterior concrete wall above grade, 3″ polyiso, sheetrock. Concrete will be waterproofed on outside.

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  1. GBA Editor
    Martin Holladay | | #1

    No.

  2. Riversong | | #2

    Whether and where a vapor barrier (retarder) is required depends on your climate zone and whether the interior is primarily heated, cooled, or evenly divided between them.

    If the foam board is foil-faced and the foil is taped at seams and the foam is sealed at all edges, then the foam/foil is a nearly perfect vapor (and air) barrier.

    If the goal is to prevent condensation on the inside of the concrete wall during the heating season, then you do need an air/vapor barrier on the warm side - but you may already have one.

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