If the depth of the street sewer prevents a uniform slope of 1/4 inch per foot for a 6-inch building sewer, what slope may be allowed with special permission?

If the depth of the street sewer prevents a uniform slope of 1/4 inch per foot for a 6-inch building sewer, what slope may be allowed with special permission?

• A. 1/4 inch per foot
• B. 1/8 inch per foot
• C. 1/2 inch per foot
• D. 1/4 inch to 1/8 inch per foot

Answer: (D)

When designing a building sewer, gravity flow requires enough slope to keep wastewater moving and prevent solids from settling. For a 6-inch building sewer, the standard slope is 1/4 inch per foot. If the depth of the street sewer makes maintaining that slope impractical, a special permission can allow a reduced slope. The permitted range is between 1/8 inch per foot and 1/4 inch per foot, so the slope may be set anywhere within that interval with approval. This keeps the flow by gravity while accommodating site constraints. A slope steeper than that is not needed, and a fixed 1/4 inch per foot isn’t required when special permission is granted; the allowable range covers the practical alternatives.

When designing a building sewer, gravity flow requires enough slope to keep wastewater moving and prevent solids from settling. For a 6-inch building sewer, the standard slope is 1/4 inch per foot. If the depth of the street sewer makes maintaining that slope impractical, a special permission can allow a reduced slope. The permitted range is between 1/8 inch per foot and 1/4 inch per foot, so the slope may be set anywhere within that interval with approval. This keeps the flow by gravity while accommodating site constraints. A slope steeper than that is not needed, and a fixed 1/4 inch per foot isn’t required when special permission is granted; the allowable range covers the practical alternatives.