In open valleys with two plies of mineral-surfaced roll roofing, the bottom layer width and the top layer width are

In open valleys with two plies of mineral-surfaced roll roofing, the bottom layer width and the top layer width are

• A. 18 inches, 36 inches
• B. 36 inches, 18 inches
• C. 36 inches, 36 inches
• D. 18 inches, 18 inches

Answer: (A)

In open valleys with two plies of mineral-surfaced roll roofing, the bottom layer is narrower and the top layer acts as the cap. The bottom layer is 18 inches wide and the top layer is 36 inches wide. This setup lets the wider top ply cover the bottom ply and extend up the roof slopes on both sides, providing a proper waterproof overlap and a clean edge in the valley. If both plies were the same width or the widths were swapped, you’d risk inadequate valley coverage or improper seam placement, which can lead to leaks.

In open valleys with two plies of mineral-surfaced roll roofing, the bottom layer is narrower and the top layer acts as the cap. The bottom layer is 18 inches wide and the top layer is 36 inches wide. This setup lets the wider top ply cover the bottom ply and extend up the roof slopes on both sides, providing a proper waterproof overlap and a clean edge in the valley. If both plies were the same width or the widths were swapped, you’d risk inadequate valley coverage or improper seam placement, which can lead to leaks.