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Metal drip edges along the entire roof perimeter help prevent water from running under the roof shingles and causing latent damage and costly callbacks.

Roof Edges

Metal drip edges along the entire roof perimeter help prevent water from running under the roof shingles and causing latent damage and costly callbacks.

  • Problem

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    Wicking Back
    Without a drip edge and a slight overhang, rainwater runoff and snowmelt can seep (or wick) back underneath the edges of the roof shingles and the roof decking, as well as the sidewall assembly, and behind the gutters. Lack of an overhang can also cause ice dam formation, with similar consequences.

  • Solutions

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    Stop It
    For new construction, the solution is simple: Design for and provide at least ¾-inch overhang beyond the finished sidewall plane, including trim and fascia, at every roof edge. Use a roofing cement or waterproof mastic to secure a pre-formed, sheet metal drip edge or cap under the roof felt or other protective membrane to further direct water off of the roof and over the edge, ideally into a gutter system.

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    Fix It
    If you’ve been called back to fix a moisture-related problem caused by a lack of overhang or drip cap, chances are you’ll have to replace the bulk of the affected roof section (not just the affected shingles or decking) and perhaps the fascia behind the gutters. If you can, extend the new roof deck ¾ of an inch over the sidewall planes and install a drip cap under the new felt and shingles, as described above.

“Probably the most common roofing mistake is where there is no overhang at the eave,” says Ken Pfaff of Criterium-Pfaff, a home inspection firm in Spokane, Wash. “Without a drip edge, runoff wicks back up under the roofing and leads to rot in the roof deck and/or the fascia.”

Inspectors and construction defect experts across the country often see the problem as a callback. Some even report situations where roofers neglected to account for the build-out of the siding or fascia of the sidewall, leaving the roof edge behind that intersecting plane. Others bemoan roofers who place the drip edge over the roofing felt (to keep the felt in place, they say), a reverse-flashing boo-boo that’s almost worse than not installing a drip edge at all.

Obviously, providing a slight overhang, ideally with a sheet-metal drip edge (or drip cap) along the entire perimeter of the roof (including rakes and second-floor structures), is most easily done in new construction.

But if you have to come back to replace the shingles, roof deck, and maybe some siding or trim—perhaps extensively so, if only to match the existing finishes not affected—adding a drip edge is a simple and inexpensive fix.