Roof Valley

A roof valley is formed wherever two pitched roof surfaces meet at an internal angle, creating a low channel that collects and concentrates all the rainwater from both roof planes. The drainage area feeding a roof valley can be two to four times larger than an equivalent length of single-slope eave, which means the gutter section at the valley discharge point receives proportionally more water during rain events.

In Sacramento, roof valleys are a common source of gutter overflow complaints because the standard gutter sizing for the rest of the roofline is often inadequate at the valley point. The solution is typically one or more of: an additional downspout outlet positioned directly at the valley discharge point; a splash guard (a small raised flashing installed inside the gutter to redirect water away from the gutter corner); or a 6-inch gutter where 5-inch was used elsewhere on the roofline.

Roof valley flashing — the metal sheet lining the valley itself — is a separate concern from gutter sizing. Open metal valley flashing (exposed metal running the length of the valley) and closed-cut valley flashing (shingles from one side overlapping the valley line) direct water down to the eave and into the gutter. Failed valley flashing is a roofing contractor scope item, while the gutter sizing at the valley discharge point is the gutter contractor's concern.