valley piece

A valley piece is a specialized tile or shingle installed where two roof planes meet at an angle, forming a valley. It bridges the gap between the adjacent roof surfaces and directs water runoff into the valley channel without allowing it to escape laterally into the joint. Unlike standard roof tiles, valley pieces are shaped or sized to overlap the adjacent tiles from both sides, creating a continuous, watertight seal along the entire length of the valley.

In pitched roofing, valleys are the lowest lines where two slopes intersect. During heavy rain, water concentrates and flows rapidly down these channels toward the eaves. A properly installed valley piece must withstand this high-velocity water flow and the freeze-thaw cycles that occur when water pools or seeps into gaps. The piece must also resist wind uplift, which is strongest at valleys where roof planes meet at an angle that exposes edges to wind pressure.

Materials and installation

Valley pieces are manufactured from the same materials as the surrounding roof: clay or concrete tiles, slate, or asphalt shingles. In tile roofing, purpose-made valley tiles are available with curved or angled profiles that conform to the valley geometry. With asphalt shingles, valley coverage is typically achieved by weaving shingles from alternating sides or, less commonly, by installing specialized valley strips of metal or rubberized material before shingle application. Metal valley pieces, usually galvanized steel or aluminum flashing, are also used as an independent layer beneath tile or slate to provide an additional moisture barrier.

Installation quality determines performance. Poor valley work causes water to back up under surrounding tiles, penetrate the roof deck, and saturate insulation and framing. Common failures occur when valley pieces are fastened too close to the valley centerline, creating stress during thermal expansion, or when overlap is insufficient to shed water reliably during extreme rainfall. The gradient of the valley must also be maintained to prevent pooling.

The term closed valley refers to the method in which tiles are installed fully over the valley line, concealing the valley channel itself. This contrasts with an open valley, where the valley is deliberately exposed, allowing water and debris to flow freely without obstruction. Open valleys are simpler to maintain but more visible; closed valleys are neater and preferred in finished work, but require precise tile sizing and fitting to avoid water entrapment.