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Flashing A Humpy Old Roof Valley

November 27, 2015

Flashing a humpy old roof valley requires a little give and take, and a backup plan.


This valley has seen its better days, but the critical spot, carrying water past the dormer has not leaked.

The roof will get a layer of peel and stick membrane and the valley will get an additional layer of metal flashing on top.

But first, clean up the valley of shingle scraps, loose nails, sawdust, and wood chips.

Once the valley is clean, Lynn applies a peel and stick membrane running up the valley.

Because he is working alone—or with the limited help of me, the cameraman—he covers the valley with two pieces of membrane—starting—at the bottom where he needs to tuck the membrane below the step flashing.

He uses the split-release paper on the back to stick the membrane to one side of the valley at a time.

With the first side stuck, he can adhere the other side.

Finally, he goes to the top and fills in the last section tucking it under the ridge vent.

Now Lynn can turn to installing metal valley flashing. First he snaps a straight line up one side of the valley.

The metal follows the line and is tacked in place to allow adjustment.

He uses shims made with shingles to smooth out the divots.

The top piece of flashing is trimmed to the shape of the ridge.

With the metal placed, Lynn adjusts the fit to try to smooth out the puckers, but notes that some pucker is inevitable —

—Lynn Hayward is a builder and remodeler in Northport, ME

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