What is the minimum slope required for a flat roof in terms of rise per foot of run?

The minimum slope required for a flat roof is generally recognized as 1/4 inch per foot of run. This slope is essential for effective water drainage, helping to prevent pooling and potential water damage. A slope of 1/4 inch per foot allows water to flow towards drainage points such as gutters or scuppers, reducing the risk of leaks and extending the longevity of the roofing materials.

While other options may suggest different slopes, a slope of 1/8 inch per foot would be insufficient for proper drainage, potentially leading to water buildup. A slope of 1/2 inch per foot or 3/4 inch per foot, although they would provide adequate drainage as well, are steeper than necessary for a flat roof, possibly resulting in unnecessary complexity and expense in construction. Thus, 1/4 inch per foot strikes the right balance between effective drainage and practicality for flat roof design.