3. For closed valleys (valleys covered with shingles), valley lining of one ply of smooth roll roofing complying with ASTM D 6380, and at least 36 inches (914 mm) wide or types as described in Item 1 or 2 above shall be permitted. Self-adhering polymer modified bitumen underlayment complying with ASTM D 1970 shall be permitted in lieu of the lining material.

Valleys in Steep-Slope Shingle Roofs

Code Interpretation

This section of the code defines the types of construction methods and materials required for valleys of steep-slope shingle applications. The valley is defined as the internal angle formed by the intersection of two sloping roof planes. In steep-slope shingle applications, the valley protection can be constructed in an open or closed method.

• In the open valley method, the steep-slope roofing material on both sides of the valley is trimmed at each side of the valley, leaving the valley flashing exposed.
• In the closed valley method, the steep-slope roofing material covers the valley area.

This section of the code is specific about the types of underlayment materials that are required for valley flashings in each method. In open valleys, corrosion-resistant metal must be applied over the valley substrate and two plies of mineral-surfaced roll roofing. Types of valley lining materials are listed in Table 1507.2.9.2.

 In closed valleys, one ply of smooth-surfaced roll roofing or self-adhered modified bitumen underlayment is required over the valley substrate prior to steep-slope roof cover application. Steep-slope roofing manufacturers typically provide specific materials and application requirements for valley flashing application to be used with their materials.