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Housewrap question.

J Lane | Posted in Energy Efficiency and Durability on

I am in the process of building an all brick house and had intentions of buying a radiant barrier (Wraptor Plus) house warp for my house in Northern Arkansas (zone 4). The product I wanted was unavailable locally so I ordered it from a building supply store out of state. I made a mistake and ordered the wrong product (regular Wraptor), so now I have a cheap woven house wrap instead which is not what I want to install. The data sheet on what I have is at this link: http://www.insulationsolutions.com/content/pdfs/wraptor/data-sheet.pdf

I am looking for advice if I should install what I have or go buy tyvek housewrap, which I can get locally. With either product I was planning on taping the OSB seams with 3m flashing tape prior to housewrap going on. The exterior will be brick with a 1″ air gap.

The other option is to buy foil faced 1/2″ polyiso (1/2″ is the most I can fit and maintain a 1″ air gap) and install over the woven house wrap. Then tape the seams of the foam. This gives me an extra R3 of insulation, helps a little with thermal bridging, and provides another layer over the housewrap at not much more cost over buying tyvek. Would this prevent drying to the outside in my climate zone?

Any advise is appreciated. Thank you

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    J. Lane,
    You wrote that you are building an "all brick house," but my guess is that you are really building a wood-framed house with brick-veneer cladding. Is that correct?

    If your house has wood framing, I strongly suggest that you include a layer of foil-faced polyiso on the exterior side of your wall sheathing. In your climate zone, 1/2-inch-thick polyiso will work. The foil-faced polyiso prevents inward solar vapor drive, and helps keep your walls dry.

    In most cases, it's a good idea to include a layer of housewrap as well, either between the polyiso and the sheathing, or on the exterior side of the polyiso. Here is a link to an article with more information: Where Does the Housewrap Go?

    As long as you have a ventilated air space between the brick veneer and the polyiso (or between the brick veneer and the housewrap), it isn't too important what brand of housewrap you install. For more information on brick veneer walls, see Flashing Brick Veneer.

  2. J Lane | | #2

    Thank you very much Martin. You are correct that it is wood framing with brick veneer.

    I bought enough 3m flashing tape to tape the seams of the OSB. Should I skip taping the OSB seams and instead tape the seams of the foam? I plan on doing a very thorough job of air sealing everything possible on the inside.

  3. GBA Editor
    Martin Holladay | | #3

    J. Lane,
    If you have enough tape and patience to tape both the OSB and the foam, go ahead and tape both.

    If you only have enough tape and patience to tape one layer, then tape the OSB.

  4. Expert Member
    Armando Cobo | | #4

    FYI - With Dow rigid foam, when you tape the foam it becomes a water resistant barrier. I imagine same may happen with other rigid foams. A taped OSB is not a WRB.

  5. GBA Editor
    Martin Holladay | | #5

    J. Lane,
    It takes more than just tape to transform Dow Styrofoam into a WRB. For more information on this issue, see Using Rigid Foam As a Water-Resistive Barrier.

  6. J Lane | | #6

    Thanks. Yes I am not planning on the OSB being a WRB just wanted to tape the seams for air sealing. Same with the polyiso, what I am using is not rated as a WRB substitute so I plan on keeping the housewrap over the OSB the the polyiso over the housewrap.

  7. D Dorsett | | #7

    IRC2012 code min for zone 3 is 2x6/R20 or 2x4/R13 + R5 continuous insulation. If you're putting only 1/2"/R3 polyiso on the exterior, it has to be 2x6 framing to meet code

    http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

    The sheathing will not be able to dry into the masonry cavity, but that's fine. It does mean you can't use vapor imperable interior finishes such as foil or vinyl wallpapers. Standard interior latex will be fine.

    If the framing is already up and it's 2x4 rather than 2x6, you'll come close to code-min performance with R15 cavity fill (1.8lbs density or higher blown fiberglass, or standard rock wool batts), but it would be better to install 1" inch of rigid polyiso on the framing only (edge strips) and either use compressed lower density batts or blown fiberglass/cellulose to fill the 4.5" depth and long-screw the wallboard through the foam. Do NOT settle on 3-3.5" of closed cell foam to meet the center-cavity R of R20, since it's performance is robbed by the thermal bridging of the 22-25% framing fraction, and barely outperforms 1.8lb density R4.25/inch fiberglass in "whole wall R" after factoring in the thermal bridging of the framing. With R6 interior + R3 exterior thermal breaks on the framing it'll beat code even with R3.5/inch low density cellulose.

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