What is the main concern with roll roofing regarding water drainage?

The primary concern with roll roofing in relation to water drainage is ponding. Ponding refers to the accumulation of water on a flat or low-slope roof surface that does not drain properly. This can occur when there are insufficient slopes or drainage pathways for water to flow off the roof, leading to water pooling.

Ponding can have several negative effects on a roof system, including:

1. Increased Weight: Accumulated water adds extra weight to the roofing structure, which can potentially lead to structural issues over time.

2. Material Deterioration: Prolonged exposure to standing water can lead to degradation of the roofing material, especially in roll roofing systems, which are typically made from asphalt. This can contribute to leaks and the overall reduced lifespan of the roofing material.

3. Mold and Mildew Growth: Standing water can create an environment conducive to mold and mildew growth, which can pose health risks and also further damage the roofing and underlying structure.

Understanding and addressing the risk of ponding is crucial in the design and maintenance of roofs using roll roofing materials. Ensuring adequate drainage and slope is essential to mitigate this concern and maintain the integrity and longevity of the roofing system.