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Community and Q&A

Flashing detail where roof meets upper wall

Scott Wilson | Posted in General Questions on

I have seen several images from siding manufacturers showing their siding installed so that the bottom edge is tight against the top of an adjoining roof (pic 1). How much of a gap should be left between the siding and the roof, not only along a horizontal section but also along a diagonal section (pic 2)?

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  1. Expert Member
    Michael Maines | | #1

    Scott, your images didn't load, but in any case it depends on the type of siding. Vinyl siding and Boral Truexterior siding can be placed directly on the roof below. Wood or fiber-cement siding should be held up at least 3/4" or 1" above the roof shingles, though that rule isn't always followed, creating steady repair work.

  2. Deleted | | #2


  3. Scott Wilson | | #3

    Michael, I just found this article by Martin Holladay. I don't know why the pictures won't load.

    Under Rule #9 he states: "Step flashing should be generously sized; the vertical leg should be at least 6 inches high, although 8 inches is better. Remember, you aren’t going to be bringing your siding down to the roof, so at least 3 inches of step flashing will remain visible under your siding. Each piece of flashing should be bent from a piece of sheet metal measuring at least 8 inches by 12 inches; crease the flashing so that it has two 6-inch-wide legs."

    That covers step flashing, but what about the flashing that runs horizontally along a roof ridge that meets a second story wall? Should you also leave about 3" of gap between the bottom of the wall siding and the lower roof?

    1. Expert Member
      Malcolm Taylor | | #4


      The purpose of the gap on step flashing is twofold. To stop moisture getting into the siding by capillary action, and to leave a gap so debris doesn't accumulate. Depending on the particular circumstances of a build I'd argue the gap could be a small as an inch. Martin is right, and what he advocates makes sense, but if like most roofers you are buying your step flashing pre-finished and pre-made at the lumberyard, the dimensions in both directions are too small to go with the reveal he suggests.

      Without a picture I'm still hazy as to which flashing you are describing in the second part of your post.

  4. Paul Kuenn | | #5

    Scott, there is a lot of splash back at the top of the ridge if your using standard shingling because of the rounded cap shingles but again, it depends on the siding for gap size. Even with vinyl, I like to leave a half inch for easy leaf cleaning in fall. If it's tight to shingles, the leaves really get jammed under the track. For flashing, I like to buy from HVAC guys who keep lots of color (anodized) aluminum in stock rolls about 2 feet wide so you can cut to any dimensions.

  5. Scott Wilson | | #6

    Malcolm, think of a two story house with a one story porch shed roof butted up against it running across the entire front of the house. The point where the upper edge of the porch roof meets the wall is the area I'm concerned with.

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