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Is a 1/4 gap in rainscreen enough?

GBA Editor | Posted in Plans Review on

Your advice and articles are topnotch. I wish I had been reading them before now. Thank you in advance for your help. I am renovating the east wall of my home in northern Vermont. For the past two months the wall has sat- OSB covered with Tyvek. I plan to side this wall with fiber-cement clapboards to match the rest of my house. The OSB is there and the windows are well-flashed, so I would rather not mess with them. I see that many sources recommend a 3/8 in. air gap in the rainscreen. If I do this I must reflash my windows. Do you think a 1/4 in. gap is adequate?

I look forward to your response and your thoughts on the matter.

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Replies

  1. wjrobinson | | #1

    Jeff, the space created by claps works for your siding for your climate. And a
    1/4" space is fine too. Breaking the capillary action doesn't take much. BSC says millimeters work even. Brick and solar drive I guess are the more problematic builds.

  2. silkwj | | #2

    The problem with smaller gaps is that, in theory, the little wrinkles etc in the Tyvek could block the airflow. But with clapboard, you've got little sideways paths to help out as well. I just retrofit a cedar clapboard wall (that had peeling paint) with a 1/4" gap, no more than that for the same reason you've got - existing windows and not much room for extra space. Only time will tell if 1/4" is truly enough, but I think it should be.

  3. DickRussell | | #3

    You should note that the HomeSlicker product from Benjamin Obdyke (http://www.benjaminobdyke.com/visitor/product/key/homeSlicker) comes in two thicknesses. Plain HomeSlicker is 1/4" thick, and HomeSlicker 10 is 11 mm (over 3/8") to satisfy Canadian requirements where a 10 mm rainscreen is required.

  4. Expert Member
    MALCOLM TAYLOR | | #4

    To optmize drying a 10mm cavity open on both the top and bottom is necessary. But those specifications were developed for the coastal rain forests of BC. A simple capillary break is more than adequate for Vermont.

  5. GBA Editor
    Martin Holladay | | #5

    Jeff,
    I think that a 1/4 inch gap is adequate.

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