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Rainscreen behind stucco for closed-cell foam insulated wall?

Andrew Shu | Posted in Energy Efficiency and Durability on

Hello,
I have a question regarding the need for a rainscreen between the lath and building paper on a closed cell insulated wall. What is the best way to do this, and is this necessary if the building is in southern California? I have two inches of closed-cell spray polyurethane foam sprayed against interior of the plywood sheathing.

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Andrew,
    I strongly advise you do include a gap between the stucco/lath/building paper and your plywood wall sheathing.

    This article includes the information you need to know: To Install Stucco Right, Include an Air Gap.

  2. Andrew Shu | | #2

    Thanks for your response. Would the gap be between the lath and building paper or between the building paper and sheathing?

  3. GBA Editor
    Martin Holladay | | #3

    Andrew,
    The answer can be found in the article I linked to. You'll need at least two layers of WRB material (for example, asphalt felt): One behind the three-dimensional plastic drainage mat, and one in front of the three-dimensional plastic drainage mat.

    In the article, I wrote:

    “If you’re installing stucco over OSB or plywood, here’s how to create a ventilated rainscreen gap:
    Install at least one layer of WRB — housewrap, asphalt felt, or Grade D building paper — over the wall sheathing.
    Install a three-dimensional plastic drainage mat (for example, Cedar Breather) over the WRB. It’s also possible to purchase all-in-one products that marry a three-dimensional plastic mat with a WRB backing. Such products include the WaterWay rainscreen drainage mat, the Korax Stucco Rainscreen Panel, the Home Slicker Stone & Stucco rainscreen, the Mortairvent mortar deflection and ventilation system, and Delta-Dry.
    Install at least one more layer of asphalt felt or Grade D paper on top of the drainage matrix.
    Install galvanized (expanded metal) or fiberglass lath, and proceed with a standard installation of three-coat stucco.”

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