The minimum slope recommended for a composition-shingle roof is 2:12. This means that for every 12 horizontal units, the roof should rise at least 2 vertical units. A slope of 2:12 is significant because it helps to ensure proper drainage of rainwater, reducing the likelihood of leaks and water pooling on the roof surface.
If the slope is too low, there is a higher risk of water infiltration, which can compromise the integrity of the roofing materials and lead to potential damage to the structure beneath. A 2:12 slope offers a balance between aesthetics and functionality, making it a standard practice in roofing installation for this type of material.
In contrast, steeper slopes provide better drainage but might not be necessary for all applications. Slopes greater than 2:12, such as 3:12 or 4:12, may be used to enhance drainage further, but they are not considered the minimum for composition shingles. The 1:12 slope is too low and is generally not suitable for shingle roofing, as it may cause more issues with water management.