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Community and Q&A

Vapor Permeable Exterior Insulation

user-6425079 | Posted in Green Products and Materials on

I can’t seem to find any Rockwool or Gutex products for my exterior insulation.  We already have a vapor barrier on the interior side of the wall, so, I’ll need a permeable option on the outside…at least I assume I do.  Any ideas?  It’ll be corrugated metal siding.  Could I compress 2×4 Rockwool batt?  I could skip the exterior insulation, but I’d rather not.

It’s been a while since I’ve paid attention to what the current practices are.




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  1. Jon_R | | #1

    The right thickness of unfaced EPS will work well.

    Use the upper right search button for more info.

  2. Expert Member


    Make sure to vent the bottom of your corrugated metal cladding.

  3. Expert Member
    Akos | | #3

    My go to budget permeable foam is fiber faced roofing polyiso. This comes with a fiberglass facer, depending on the manufacturer and thickness, it tends to be above 1 Perm.

    The facer on this foam absorbs water, so your WRB needs to go over the foam. If this is not a type of install your contractor is comfortable with, go for unfaced EPS/GPS or low GWP XPS foam as Jon R suggests.

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