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Community and Q&A

Siding over T1-11

J6204 | Posted in General Questions on

I have a house with T1-11 as it’s siding/ sheathing. It has a flat roof and no overhang. I want to put horizontal and vertical siding over the T1-11 with some  WRB and coraplast strips behind it. The facia has vents drilled in it currently. In this case would you recommend eliminating the vents. ( the roof has virtually no pitch ). Would you create an air gap at the top of the siding or not?

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  1. Expert Member
    Dana Dorsett | | #1

    I need a picture to visualize more clearly what's going on here.

  2. Expert Member


    Rain-screen cavities perform better when vented top and bottom - but they perform just fine when vented at the bottom only.

    I'm sorry, I don't have enough experience retrofitting flat roofs to comment on the fascia-vents.

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like you are asking two questions -- one about the usefulness of a rainscreen gap behind your siding, and one about the best way to vent a low-slope (flat) roof.

    For more information on rainscreen gaps, see this article: "All About Rainscreens."

    For more information on venting a low-slope (flat) roof, see "Insulating Low-Slope Residential Roofs."

  4. J6204 | | #4

    This is what it looks like

  5. user-1072251 | | #5

    Building Science has a graph (which I cannot find right now) showing the depth of overhang compared to damage from water running off the roof to siding - turns out that the larger the overhang, the better the siding holds up. Before you add new siding, increase your overhangs.

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