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Community and Q&A

Tyvek DrainVent Rainscreen or two layers of Jumbotex?

kpklein | Posted in General Questions on

Saw this Tyvek DrainVent Rainscreen product on the Musings of an Energy Nerd blog. Here in Southern California, it’s typical to see two layers of Jumbotex used under stucco. What would you choose: Tyvek wrap, with two layers of Jumbotex, then stucco? Or: Tyvek wrap followed by Tyvek DrainVent, then stucco? The DrainVent seems to be a more consistent way to get the necessary drainage gap under the stucco. Would a layer of Rigid Polyiso Foam board be a good idea also? What would be the recommended way (where in the assembly) to incorporate a layer of Polyiso board? Tyvek wrap, Polyiso board, Tyvek DrainVent, then stucco?

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, have you read this article?
    "To Install Stucco Right, Include an Air Gap"

    Second: Builders with a long memory remember that in the 1980s, there were reports of Tyvek disintegration due to Tyvek contacting stucco. DuPont responded by reformulating Tyvek, but I've been leery of any detail that allows Tyvek to contact stucco ever since those memorable failures.

    You might consider installing Tyvek DrainVent rainscreen followed by two layers of Jumbotex. Or you might follow the advice in my article, and include a three-dimensional plastic drainage mat in your assembly.

    1. kpklein | | #2

      Hi Martin,

      Thank you for your reply. I just read your article, great info! I like the idea of plywood (how about pressure treated for the bottom 24”?), Jumbotex, rain gap product, then the second layer of Jumbotex. (With generous overhangs and properly flashed openings). New questions: can you recommend your current favorite rain gap product? And do you think I am safe to omit exterior foam? I am concerned after reading/learning about the possibility of condensation on the (cold) interior side of the sheathing. (Planning 2x6 or 2x8 walls with unfaced batt insulation, drywall, wood, paint, and so on). Should I not be concerned about this condensation issue here in SoCal and skip the rigid foam? I prefer to not use it and keep the wall as simple as possible...

  2. Expert Member
    Peter Yost | | #3

    The double layer of building paper with stucco is so that the outer layer serves as a bond break with the stucco, allowing the second interior layer to manage any water that gets to it.

    My understanding of the building paper (from Joe Lstiburek back in my Building Science Corp days) is that the outer layer crinkles up as it takes on moisture and that creates drainage pathways, the old-fashioned way, between the two layers of building paper.


    1. kpklein | | #4

      Thanks Peter, appreciate the reply. I have a copy of Joe’s book and read that about the two layer paper approach. A high-builder here (he doesn’t work in my area, and I couldn’t afford him if he would) likes to start with a layer of Tyvek, then the two layers of Jumbotex. He won’t use anything that hasn’t been in wide use for at least a decade. So no Zip Sheathing for example. I’ll just keep it simple and use the two layer approach, and probably the Tyvek for good measure. Risinger has the idea of using pressure treated plywood for the bottom two feet of sheathing, not a bad idea too. Is there any danger of condensation forming on the interior of the sheathing in SoCal or is it too warm here for that to be a factor?

  3. user-2642926 | | #5

    So Cal has a variety of environments. For one of the Pros on the board to answer your question about wall cavity condensation, where are you located and what is the zone?

    I'm in So Cal. I went with exterior polyiso not for the winter performance but for summer. Breaking that thermal path from exterior to conditioned space is useful in all the extremes of the year though.

    1. kpklein | | #6

      Thanks Mike, I’m in De Luz, zone 3 (inland/dry), an area in the hills west of Temecula, CA...

  4. Granular | | #7

    Joe Lstiburek always recommends exterior insulation - it's his Perfect Wall (and roof and floor) assembly. Go watch some of his hour-long presentations on YouTube - well worth your time.

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