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Community and Q&A

Ventilated rainscreen

ERIC WHETZEL | Posted in Green Building Techniques on

Our wall assembly mostly copies Hammer and Hand’s Madrona House project, so we will have 2 layers of Roxul over our Zip sheathing, followed by 2 layers of 1×4 battens or furring strips (first layer vertical, second layer horizontal), before the cedar siding is finally installed on the second layer of horizontal 1×4’s.

My siding installer was asking about the possibility of moisture being trapped at the interface between the vertical and horizontal layers of 1×4 battens. Does anyone believe this is likely, or worth thinking about?

In a YouTube video at their Madrona House project, Sam Hagerman notes (around the 2:58 point) that they expect up to hundreds of air changes per hour with this kind of wall assembly and rainscreen set-up. Based on this, and other things I read during the design stage, this seemed reasonable.

Any reason to believe otherwise?

I know Hammer and Hand strongly emphasize the importance of maintaining an air gap at the top and bottom of the walls (using Cor-A-Vent strips) to facilitate this kind of air movement, so as long as this is maintained around the structure I should be ok, right?

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  1. GBA Editor
    Martin Holladay | | #1

    Most types of siding shed rain water, and most rainscreen gaps are quite dry. The exception concerns so-called "open-joint" siding (or "open-gap" siding) -- a type of siding that leaves deliberate gaps between panels or boards. You didn't describe your siding, but I'm guessing that you will install board-and-batten siding.

    Assuming that your siding doesn't have open gaps, your siding installer's worries are baseless.

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