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Ice and Water shield on an exterior wall….. ? asking for trouble

mclola | Posted in General Questions on

For our home in zone 5 (Syracuse, NY) which had some moisture intrusion issues over the last 50 + years – we were planning to replace the plywood/felt/Tyvak with Zip R9 sheathing and interior Rockwool batt insulation in our 2 x 4 and 2 x 6 walls (different areas of the home built at different times); and use a rainscreen under the siding.  

My question now applies to the ice and water barrier installed last month while the roof was being repaired.  From the photo, you can see the black shield extends from the side of the roof up the wall with 2 picture windows.   The interior of this wall is mainly a bedroom, and only a small portion is an unconditioned attic.   It seems to me this may contribute to moisture trapping in the wall unit which could lead to mold/rot in the future.  

Can this be used with the Zip R system on this particular wall, or would it be best to take it down and install the Zip R as planned?   I have already asked the contractor not to use this on any other walls.

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  1. Expert Member
    Michael Maines | | #1

    It's not ideal, and if you were not planning on using continuous exterior insulation it would eventually result in rot due to outward vapor drive. But knowing the kind of snowstorms you get in Syracuse, I can see why you would want extra protection on that cheek wall. R-9 Zip-R sheathing should keep the condensing surface warm enough that it should be a reasonably safe assembly.

  2. mclola | | #2

    Yes, the contractor stated he was concerned about standing snow causing moisture in that wall. I am glad to hear the R9 Zip should help keep moisture from condensation down. Would this be one wall to consider using an interior 'smart' vapor retarder on such as MemBrain? Thank you.

    1. Expert Member
      Michael Maines | | #4

      Yes, it's not required by the IRC building code if you have enough exterior insulation, which you do, but since your wall will have zero drying ability to the exterior, adding a variable permeance membrane would be good insurance.

      1. mclola | | #5

        Thank you for the additional information - I will plan on having a variable permeance membrane on that wall.

  3. mikeolder | | #3

    How about advantech sheathing? Ive read some contractors regularly install
    it around the lower perimeter.

  4. mclola | | #6

    Hi Mike, I am not too familiar with advantech sheathing. Which part of the wall assembly would the advantech be used on, and would it replace the Zip? Thanks.

    1. mikeolder | | #7

      Same company..

      It would be used on the exterior, but I dont think you can get it insulated and I'm not sure on the permeability.

      The glue is a advanced resin technology.. Good stuff from what Ive read.

      1. Expert Member
        Michael Maines | | #8

        Adventech is good stuff and more resistant to moisture damage than most OSB, but if it remains damp it will eventually fail. (I've had a piece of 3/4" Advantech outdoors in my chicken run for eight years and it's still intact but rotting at the bottom.)

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