Siding over T1-11

J6204 | Posted in General Questions on November 15, 2018 11:11am

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?

Answer

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Replies

Expert Member

Dana Dorsett | Nov 15, 2018 05:36pm | #1
I need a picture to visualize more clearly what's going on here.
Expert Member

MALCOLM TAYLOR | Nov 15, 2018 06:23pm | #2
Jim,

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.
GBA Editor

Martin Holladay | Nov 16, 2018 05:17am | #3
Jim,
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."
J6204 | Nov 16, 2018 09:42am | #4
This is what it looks like
user-1072251 | Nov 16, 2018 11:57am | #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.