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Installing rain screen wood siding over stucco??

rebeccamichelle | Posted in Energy Efficiency and Durability on

Hi there. I’m working on a project in Oakland, CA (coastal/foggy) where, due to the winter’s rain/water damage, we are removing stucco from the chimney volume of the 2004-built wood-framed house and replacing it with new sheathing and a rain screen siding system, the contemporary type with 1/4-1/2″ gaps between the horizontal boards, not shiplap or t&g. That’s all fine (I think).

The question is that at the garage volume of the house the stucco is undamaged, and they want to have the same look of horizontal slat rain screen in that area as well. The contractor has said we would just attach 3/4″ furring strips directly to the stucco, then attach the horizontal siding to the furring strips. I asked a waterproofing consultant about this and he said that this would cause “spectacular mold growth” on the stucco under the siding.

As I’ve looked around the web, I see lots of posts about attaching siding to stucco and no one mentions concern about the mold growth. I thought the 3/4″ air gap and air gaps at the top and bottom of the rain screen are meant to allow air to circulate, and potentially avoid mold growth? Please share any thoughts/advice/experience with this application.

See attached images – we’re proposing the siding at the areas where the stucco is painted red.

Thank you!!

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  1. user-2310254 | | #1

    Is this real stucco or EIFS. I suspect that real stucco has more potential to act as a moisture reservoir. EIFS (synthetic barrier over EPS) is probably less problematic (assuming it was installed correctly).

  2. Jon_R | | #2

    With the stucco being protected from most rain and having free air flow, I'd say less mold than shaded stucco alone. But some possible ideas for extra insurance - spray the stucco with Wet&Forget and install Delta Fassade S under the new siding to stop wind driven rain.

  3. rebeccamichelle | | #3

    It's real stucco. Thank you - this is helpful info!

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