CSLB C-36 Plumbing ContractorRough-in PlumbingMedium
A plumbing contractor is installing a new drain, waste, and vent (DWV) system. A water closet (toilet) is being installed, and its trap arm extends 4 feet horizontally to connect to a 3-inch vertical stack. What is the maximum allowable length for this 3-inch water closet trap arm, according to the California Plumbing Code (CPC)?
- A2 feet 6 inches
- B3 feet 6 inches
- C5 feet 0 inches
- D6 feet 0 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 6 feet 0 inches
The California Plumbing Code limits the developed length of fixture trap arms to prevent trap siphonage and ensure proper venting. For a 3-inch water closet trap arm, the maximum developed length is 6 feet.
Why the other options are wrong
- A. 2 feet 6 inches is the maximum for a 1 1/2-inch trap arm.
- B. 3 feet 6 inches is the maximum for a 2-inch trap arm.
- C. 5 feet 0 inches is not a standard maximum length for a 3-inch trap arm.
Water Closet Trap Arm Length
The maximum allowable developed length of the pipe connecting a water closet trap to its vent or vented branch, ensuring proper trap seal protection.
- Prevents trap siphonage and back pressure.
- Varies by trap arm diameter.
- Specified in the California Plumbing Code (CPC).
Memory trick: Traps Take Tiny Travels.