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Exterior foam board

Csk | Posted in General Questions on

Have a house in zone 5 Michigan with r 19 Kraft faced insulation on interior. Would like to put ridgid foam board on outside. Trying to figure out what kind and should it be foil faced or not

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  1. Expert Member
    Michael Maines | | #1
    1. Csk | | #2

      Thanks for the help it is appreciated


  2. Expert Member
    BILL WICHERS | | #3

    I prefer polyiso, for maximum R per inch. You can usually use either foil or fiber faced rigid foam on the exterior, as long as your walls can dry to the interior. The big difference is that foil or poly faced rigid foam is a vapor BARRIER, and allows ZERO drying. Fiber faced rigid foam is a pretty tight vapor RETARDER, and allows a LITTLE drying. In practice though, walls built with exterior rigid foam are normally intended to dry to the interior, so it ends up not making much difference which type of facer is on the exterior rigid foam. If you have interior polyethylene that you can't remove, that's when I'd use fiber faced rigid foam, or rigid mineral wool (even better for drying, buy lots more expensive).


    1. Csk | | #4

      Thanks for the advice bill


    2. Expert Member
      Deleted | | #5


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