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Wall Sheathing & Roof Flashing

Rachel | Posted in Construction Techniques on September 21, 2007 03:14am

I am re-siding my house and I’m interested in creating as much protection against water intrusion without going completely overboard and I’m trying to make a decision on what to do at the four places where wall meets roof. Here’s what I’ve got, what I’ve done and what I’m thinking.

WHAT I’VE GOT: Wood frame, tar paper, wood sheet siding, asphalt shingles, step flashing that goes behind the siding/over the paper.

WHAT I’VE DONE: Tore off siding and paper. Installed struc-1 sheathing (I’m in CA so I’m retro-fitting for EQs) over step-flashing. Planning to wrap and then side w/fibercement sheet product.

WHAT I’M THINKING: Having been traumatized by water intrusion in the past, I’d like to do something to protect the sheathing. I have lots of ideas but wonder whether they are just weird or are likely to be ineffective. Keep in mind that I don’t want to have to touch the roofing. Options: (1) Paint the sheathing w/copper green, stick Bituthene to bottom edge of sheathing and run up the sheathing (don’t stick to flashing because of expansion/contractions needs), install siding. (2) Slather some sort of sealant on the bottom edge of the sheathing and up 8 inches (again don’t stick the sheathing to the flashing w/this), install siding. (3) Install additional step-flashing over the sheathing, working under the shingles as best I can w/out having to take out any shingles, install siding. (4) Paint sheathing w/copper green, install a piece of L-flashing painted to blend w/the roof that sits over the shingles, install siding.

Options 1 or 2 are the easiest but also (perhaps) the least orthodox. I really want to avoid Option 3 because I don’t want to touch the roofing. I recognize that Option 4 is really only about kicking water that hits the wall out onto the roof and I wonder if it creates a possible problem by holding (hydrogen bonding) water in the wall- roof junction.

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Replies

  1. User avater
    SamT | Sep 21, 2007 04:18pm | #1

    Sheathing.

    Step flashing. Start at bottom on top of bottom shingle, slide under second shingle. Flashing covers shingle underneath and slips far under shingle above. Repeat on top of second shingle under third. Repeat to top. Nail to sheathing at top of flashing. Deal with top flashing.

    Drain plane/rain-stop lapped over step flashing. Tar paper, Grace I&W, Bituthene. Depends on siding. Ok to adhere to step flashing.

    Siding.

    Tar paper allows moisture vapor in sheathing to pass to outdoors. Water that gets behind siding hits drain plan, runs down to top of step flashing, then to top of shingles.

    You can paint the step flashing.

    SamT

    1. Rachel | Sep 21, 2007 04:23pm | #2

      Thanks for the reply. Let me get this straight. You're saying to go w/my Option 3. Am I risking busting my shingles that have been in place for seven years and the tabs are now brittle and have probably adhered to each other? Do I just carefully work this additional step-flashing in?

      1. User avater
        SamT | Sep 21, 2007 05:02pm | #4

        I am assuming the the shingles stop before the sheathing. IOW, the vertical plane of the face of the sheathing does not hit the shingles.If that's not so, cut the shingles so the flashing can go over the wall sheathing and under the shingles. The shingles should stop ~1/2" before hitting the sheathing. Caulk or foam the gap between the wall and roof sheathings. Turn the edge of the roof tar paper up onto the wall sheathing under the wall drain plane. If this was new construction, I'd say about 6", but whatever you can get, if any.When the bottom piece of step flashing hits a shingle nail, mark it and cut it so it doesn't extend past the eave edge of the shingle. The rest of the flashing can be cut to fit or left to run long. Unless you import some freezing weather into the East Bay, the shingles will be flexible enough to slide the 20ga - 16ga galvanized sheet metal step flashings between them. The edges will cut through any adhesion. Stop when you touch a roofing nail.Let me edit my post #2 above:
        "Step flashing. Start at bottom on top of bottom shingle, slide under second shingle."
        should read
        "Step flashing. Start at eave on top of bottom shingle, slide under second shingle."SamT

        1. Rachel | Sep 21, 2007 05:05pm | #5

          Thanks again. I'll keep in mind that water runs DOWN and start at the bottom.

    2. Rachel | Sep 21, 2007 04:27pm | #3

      Reading Sam T's Reply made me realize that I'd failed to mention building wrap immediately before "install siding". I'm one of the crazy people who do the "performance" installs when flashing windows. People may make fun of me for it but on a rainy day I'm not worrying about those wall penetrations.

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