correct horizontal gap between t1-11 panels?

mixwhitJuly 9, 2009

The bottom of my t1-11 type siding is rotting in places. To fix, I've been cutting off the bottom 20" (a height safely above the rot) and installing new panels. But now that it's raining like mad I can see that the upper panels are wicking water up from the flashing. You can see it on the inside of the garage, above the flashing's lip. And outside I can see that water is just sitting in that gap and holding there.

How big should the gap be between the flashing and the panel above it?

I set mine at 1/8" after following the suggestion on the This Old House site:,,1064764,00.html . I"m thinking now that this isn't big enough.

The other question is whether maybe the flashing needs a bit of a downward angle to it? The flashing I have is all 90 degree angles. 2" for the rear, 5/8" for the kickout, and not much for the lower part (maybe 3/8"). Perhaps I should install the flashing, then bend it downward a bit, and then nail the new panel underneath, but without pushing the flashing back up?

Here's what I did in more detail:

-bought new siding, cut into 20" tall pieces, and stained faces and edges

-cut the bottom 20" off the house

-stained the newly cut edge

-slipped z-flashing up under the new cut edge and left 1/4" gap between the bottom of the upper panel and the flashing

-overlapped flashing seams at least 2"

-nailed the flashing in place through the siding right at it's top (about 2" above the kickout point of the flashing)

-ran a bead of caulk across the top of the new panel

-slipped the panel underneath the flashing, held firm up against the flashing, and nailed into place with 8d galvanized ring shank nails

Thanks for any help!! It looks like I'll have to tear off all this work and try again.

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If you're saying that water is sitting in the horizontal part of flashing then, yes I'd say you need to slope that part to the outside so it rolls off.

I'm not sure what your bead of caulk does but it couldn't hurt.

Hope this helps.

    Bookmark   July 9, 2009 at 3:53PM
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Cut the bottom edge of the sheets to a 30 degree angle, and keep it 1/4" above the flashing. Most important!: prime the bottom edge, and up a foot on the back side. Use oil primer. Maybe even go so far as to pre-paint the bottom edge before installing. This detail will keep the water dripping off the plywood, and prevent it becoming waterlogged.

    Bookmark   July 9, 2009 at 10:07PM
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