What is the valley on a roof called?

The valley on a roof is simply referred to as a roof valley, which is the internal angle or V-shaped channel formed where two separate roof slopes meet and intersect. Because these areas collect and channel large volumes of rainwater and melting snow running off both intersecting planes, they play a critical role in the overall drainage system of a home. Depending on the architectural style and aesthetic preferences of the homeowner, roof valleys are categorized into a few distinct types: open valleys, which feature an exposed metal channel down the center; closed-cut valleys, where shingles from one roof plane continue smoothly across the intersection; and woven valleys, where shingles from both sides alternate and overlap in a crisscross pattern. Regardless of the specific construction method, the roof valley must be reinforced with robust waterproof underlayment and flashing to prevent moisture from penetrating the home.