What is the slope required for a built-up roof in terms of rise to run?

A built-up roof typically requires a minimum slope of 1/4 inch rise per foot of run. This ratio is essential for ensuring proper drainage, preventing water pooling on the roof, and reducing the risk of leaks and structural issues over time. The 1/4 slope allows water to flow towards drains or scuppers, facilitating effective runoff and helping to maintain the integrity of the roofing materials. A lower slope, such as 1/8 or 1/16, may not provide adequate drainage, leading to potential water accumulation, which can compromise the roofing system's lifespan. On the other hand, a slope of 1/2 might be unnecessarily steep for most built-up roofs, increasing the complexity and cost of installation without added benefit. Thus, the requirement of 1/4 inch rise to 12 inches run is established as a standard to balance drainage efficiency and maintain roofing performance.