What minimum slope per foot is permitted for a 3 inch building drain?

For a 3-inch building drain, the minimum slope permitted is set to ensure effective drainage and prevent the accumulation of waste and water in the pipe. A slope of 1/8 inch per foot is commonly accepted as a standard minimum for pipes of this size. This slope allows gravity to assist in the movement of wastewater and reduces the risk of clogging, which can occur with insufficient slope.

When the slope is too shallow, such as 1/16 inch per foot, there may be a higher potential for debris to settle within the pipe, leading to blockages over time. Conversely, a slope that is too steep, like 1/2 inch per foot, could result in water flowing too quickly, potentially leaving solids behind and contributing to clogs.

Choosing a slope of 1/8 inch per foot balances the need for effective gravity drainage while minimizing the risk of sediment buildup or other drainage issues, making it the most suitable choice for a 3-inch building drain system.