CSLB C-36 Plumbing ContractorRough-in PlumbingEasy
A plumbing contractor is installing a new residential drain, waste, and vent (DWV) system. What is the minimum required slope for a 4-inch horizontal drainage pipe?
- A1/16 inch per foot
- B1/2 inch per foot
- C1/8 inch per foot
- D1/4 inch per foot
Show answer & explanationAnswer & explanation
Correct answer: C. 1/8 inch per foot
According to the California Plumbing Code (CPC), horizontal drainage pipes 3 inches or larger in diameter require a minimum slope of 1/8 inch per foot to ensure proper drainage and prevent clogging.
Why the other options are wrong
- A. This slope is typically too shallow for effective drainage in pipes 3 inches or larger.
- B. This slope is excessive and not generally required for horizontal drainage pipes, potentially causing issues with water sealing traps.
- D. This slope is typically required for pipes smaller than 3 inches in diameter.
Horizontal Drain Slope (Large Pipes)
The minimum downward angle required for horizontal drainage pipes 3 inches or larger in diameter.
- Ensures proper waste flow.
- Prevents solids from settling and causing blockages.
- Specified by plumbing codes.
Memory trick: Sloping drains keep things moving, like a gentle downhill stream.