Open valley lining consists of how many plies of mineral-surfaced roll roofing?

• A. One ply
• B. Two plies
• C. Three plies
• D. Four plies

Answer: (B)

Open valley lining typically consists of two plies of mineral-surfaced roll roofing. This construction method is employed to enhance the durability and waterproofing of roof valleys, which are crucial areas where water can accumulate and flow down the structure. The two-ply system allows for a more robust barrier against potential leaks, as each ply over-laps, reducing the chances of moisture penetration.

Having two plies also helps in accommodating the thermal expansion and contraction that roofing materials undergo. This is particularly important in regions with varying temperatures and weather conditions. By using a mineral-surfaced roll roofing, the surface can withstand UV exposure and wear better over time, making it a suitable choice for roofing applications.