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Durable WRB for rainscreen

Marylandgunner | Posted in General Questions on

I am residing my 1972 built home. Removing vinyl siding over cedar board and batten over celotex sheathing. The new wall assembly will be CDX plywood, WRB, climate shield ipe rainscreen siding on aluminum clips.

The rainscreen is vented as there there is 1/8” gap between the grooves in the boards. But it is not an open rainscreen because the lip of the top board overhangs the gap. So the WRB is UV-protected.

I am am pretty confident with the materials for this assembly except the WRB. I can’t figure what the best option is. Because of the fact that bulk water can get through the rainscreen I feel like I need something more durable than, say, Tyvek.

I have looked at Blueskin but the sample was thin enough I could see through the thin sections. Also I have considered Tyvek Commercial and Delta.  The very high perm rating of the Delta makes me nervous. Now I am considering Tyvek or similar and just add a layer of felt over that.  Any thoughts?

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  1. RussMill | | #1

    Tyvek STUCCO WRAP, is similar to commercial D tyvek in that its made heavier. I like stucco wrap because the rolls are 5 feet wide so its easier to handle also. If using stucco wrap dont pull it to tightly. It causes the wrinkles to flatten. Cheaper than commercial d as well. Drainwrap is another alternative. All will work BUT like you i always do a layer of tar paper over it.

  2. GBA Editor
    Martin Holladay | | #2

    You mentioned Delta -- but did you know that the manufacturer of Delta (Cosella-Dörken Products) makes several different WRBs? For more information on Vent S, Delta-Foxx, Delta-Maxx, and Fassade S, see this article: "New Green Building Products — September 2010."

    You wrote, "The very high perm rating of the Delta makes me nervous." Why? Are you worried about inward solar vapor drive? Or are you confusing vapor permeance and water-resistance?

  3. Trevor_Lambert | | #3

    Typar Metrowrap is a more robust WRB as well, and 12 month UV guarantee if that is of any concern.

  4. Marylandgunner | | #4

    I suppose I am equating permeability with water resistance. It’s seems like they would be related and the specs for water resistance are a little tough for me to decipher.

    Good to know someone does put felt over wrb. I actually drove past a house being built by the premier builder in the area. They were putting shingle siding on (couldn’t tell Cedar or synthetic) he was using Blueskin VP100 then felt then shingles. I am thinking of going this route. The Blueskin will give some air barrier and supposedly self sealing. The felt will add a little durability and black background Incase it shows through gaps where siding meets windows. And the assembly should still breath well. Is there anything I’m missing?
    I don’t a crinkle or breather wrap because the siding clips create a 3/4” gap behind the siding.

    1. GBA Editor
      Martin Holladay | | #6

      You wrote, "I suppose I am equating permeability with water resistance."

      Well, stop doing that. Virtually all WRBs are both waterproof and vapor-permeable. Manufacturers are certainly able to manufacture membranes that stop liquid water while still allowing vapor diffusion.

  5. Jon_R | | #5

    > The Blueskin will give some air barrier

    A good one, better than a non-fully adhered option. Perms also matter (see below). Blueskin + felt may be about right.

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