CSLB C-36 Plumbing ContractorRough-in PlumbingMedium
A plumbing contractor is installing a new drain, waste, and vent (DWV) system in a single-family home. The main building sewer line is being connected to the public sewer lateral at the property line. What is the minimum required slope for this 4-inch building sewer pipe, according to the California Plumbing Code (CPC)?
- A1/8 inch per foot
- B1/2 inch per foot
- C1/16 inch per foot
- D1/4 inch per foot
Show answer & explanationAnswer & explanation
Correct answer: A. 1/8 inch per foot
The California Plumbing Code specifies minimum slopes for building sewer pipes to ensure adequate flow velocity for self-scouring and to prevent solids from settling. For a 4-inch building sewer pipe, the minimum required slope is 1/8 inch per foot.
Why the other options are wrong
- B. 1/2 inch per foot is an excessive slope that can cause solids to be left behind as water rushes past.
- C. 1/16 inch per foot is generally too shallow for any building sewer pipe and would lead to blockages.
- D. 1/4 inch per foot is the minimum for smaller diameter drains (e.g., 3-inch or less) but not the minimum for a 4-inch sewer.
Building Sewer Slope
The minimum downward incline required for the main building sewer pipe to ensure gravity-assisted flow of waste to the public sewer or septic system.
- Prevents solids from settling and causing clogs.
- Ensures self-scouring velocity.
- Varies by pipe diameter, specified in plumbing codes.
Memory trick: Sewer Slopes Sustain Steady Flow.