Core TradesQuestion 154 of 700

In an open valley on a shingle roof, metal valley flashing is installed primarily to:

a.Hold the shingles down against wind uplift
b.Channel concentrated water runoff and prevent leaks where two roof planes meet
c.Ventilate the attic space
d.Serve as decorative trim

Explanation

A valley collects runoff from two intersecting planes, so metal valley flashing forms a durable, watertight channel to carry that concentrated flow off the roof. It is not primarily a fastener, a vent, or decoration; those roles are served by other components.

Law Reference: 2025 CA Residential Code §R905.2.8

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