What Is a Roof Valley?

A valley takes the water from two roof planes and concentrates it into one narrow path, so it sees more flow than any other part of the surface. There are three common ways to build one. An open valley leaves a strip of metal exposed down the center, with shingles trimmed back along both sides. A closed-cut valley runs the shingles from one plane across the valley line and cuts back the other, so no metal shows. A woven valley interlaces shingles from both planes. Underneath, a waterproof membrane or valley metal supplies the protection the shingles alone cannot.

Valleys are measured in linear feet, and the number of them says a lot about the job. A cut-up roof with many valleys, dormers, and intersecting gables takes more labor and produces more waste than a plain gable, and an estimate that treats the two alike has either overcharged one or underbid the other. Inspectors look at valleys for worn granules, debris buildup, and lifted edges, because that is where water pools and ages the roof fastest.

Valleys get mistaken for hips. A valley is an inward angle where slopes drain toward each other; a hip is an outward angle where they slope away. Field mistakes are usually about nailing: fasteners driven too close to the valley centerline create leak paths, and manufacturers specify how far back they must stay. Leaving old valley metal under new shingles carries the previous roof’s wear into the new one.