Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is installing a battery of four commercial lavatories in a public restroom. Each lavatory is assigned 1 DFU. The branch drain serving these lavatories is 2 inches in diameter. What is the maximum developed length allowed for this 2-inch horizontal branch drain before it requires a separate vent or connection to a larger vent stack?
- A12 feet
- B35 feet
- C8 feet
- D24 feet
Show answer & explanationAnswer & explanation
Correct answer: B. 35 feet
The maximum developed length of a horizontal branch drain is determined by its size and the total DFUs it serves. For a 2-inch horizontal branch drain, the maximum developed length permitted before needing additional venting is 35 feet.
Why the other options are wrong
- A. This length is often associated with smaller diameter pipes or specific vent types.
- C. This length is too short for a 2-inch branch drain's maximum developed length.
- D. This length is too short for a 2-inch branch drain; 24 feet is for a 1 1/2-inch pipe in some codes.
Horizontal Branch Drain Max Length
The maximum developed length a horizontal branch drain can be before requiring additional venting to prevent trap siphonage and back pressure.
- Varies by pipe diameter.
- Ensures adequate air circulation.
- Preventative measure against trap seal loss.
Memory trick: Longer the branch, stronger the vent.