Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsEasy
A plumber is installing a 2-inch drainage pipe in a residential bathroom. The pipe will serve a single lavatory and a shower. What is the maximum developed length allowed for the trap arm connecting the shower P-trap to its vent, assuming a 2-inch trap arm?
- A6 feet 0 inches
- B5 feet 0 inches
- C3 feet 6 inches
- D8 feet 0 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 5 feet 0 inches
The maximum developed length of a trap arm is determined by its diameter. For a 2-inch trap arm, the maximum developed length allowed by most plumbing codes is 5 feet 0 inches.
Why the other options are wrong
- A. This length exceeds the maximum allowed for a 2-inch trap arm and would likely lead to trap siphonage.
- C. This length is typically associated with smaller trap arms, such as 1 1/2-inch.
- D. This length significantly exceeds the maximum allowed for a 2-inch trap arm and would definitely lead to trap siphonage.
Trap Arm Developed Length
The maximum horizontal distance from the outlet of the trap to the vent pipe opening, ensuring proper venting and preventing trap siphonage.
- Varies by trap arm diameter.
- Critical for preventing loss of trap seal.
- Measured along the centerline of the pipe.
Memory trick: Long arm, no seal, bad smell.