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Does the facing of polyiso insulation matter when mechanically attaching to a block wall?

Paul J | Posted in Building Code Questions on

The 2009 IRC allows for unvented crawl spaces. To acheive the R-10 for my zone (Maryland) I plan on using recycled 2″ polyiso roof insulation attached with Tapcon screws to the CMU walls. 85% of the CMU is below grade. The facing of the roof insulation I intended to use has a heavy tar paper facing both sides. Does this facing preclude using this roof insulation in this application?

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  1. TJ Elder | | #1


    This is probably okay if the wall has effective waterproofing and stays dry. The polyiso will be nearly impermeable, but you don't really want moisture to migrate into the insulation. You just need to be sure there's no wetting of the block, or water could collect under the polyiso, and probably end up dripping out onto the floor. The worst thing you can do is add insulation to the warm side of a wet wall.

  2. Paul J | | #2

    Thank you for your reply.

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