International Residential Code (IRC) Plumbing Practice Test

The minimum slope for a drainage line is specified to ensure proper flow and prevent the accumulation of wastewater or sewage in the pipes. A slope of 1/4 inch per foot is established as an industry standard for most drainage applications. This slope is effective in maintaining a self-cleansing velocity, which helps to carry solids through the system and reduces the risk of blockages.

Choosing a slope too shallow, such as 1/8 inch per foot, may lead to inadequate drainage, causing sediment to settle in the line and potentially resulting in clogs. Conversely, a slope that is excessively steep, like 1/3 inch or 1/2 inch per foot, may create high flow velocities that can lead to erosion of pipe materials and noisy operation, while also increasing the chances of siphoning or trapping air, which can cause the system to fail.

Therefore, a slope of 1/4 inch per foot strikes the right balance to promote efficient drainage and system longevity, adhering to the requirements outlined in the International Residential Code.