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What type of capillary break material is this?

JohnJones171 | Posted in Energy Efficiency and Durability on

Hi all-Preparing for installing 2 inches of GPS, 2×4 stud wall, roxul, drywall.  Since I only have 1-4 inches of exposed exterior foundation for outward drying depending where along the house it is, I am a bit concerned about sill plate rot. The attached picture is the capillary break under my sill plate. Feels like a black poly material, perhaps a bit thinner then standard 6 mil if I had to guess. Toronto, zone 5.

1. What is this material?
2. Is it adequate to keep my sill plate dry, since I will be trapping moisture in the cement via the insulation potentially causing wicking to the sill?

Current insulation on the poured concrete foundation is the standard R12 builders blanket. 1979 build.

Thanks for your thoughts.

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  1. Expert Member
    BILL WICHERS | | #1

    It LOOKS like it could be either EPDM, or a polyethylene sheet. The way to tell is to do a "scratch test" with your fingernail. EPDM is a rubber-like material, and will feel a little like scratching the rubber of a car tire. Polyethylene has a very distinctive scratch-test feel, it "sticks and slips" -- it's a MUCH more slick and slippery material than EPDM.

    Either material makes an excellent capillary break though. You appear to be in good shape here. The only thing I'd consider doing is checking for any obvious tears or other damage.


    1. JohnJones171 | | #2

      Thanks Bill. Feels like poly. Much appreciated.

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