CSLB C-36 Plumbing ContractorRough-in PlumbingMedium
A plumbing inspector is reviewing the rough-in for a new multi-story commercial building. The inspector observes a common vent serving two adjacent lavatories, both located on the same floor level. What is the maximum developed length permitted for the common vent from the farthest trap weir to the vent connection?
- A5 feet
- B6 feet
- C2 feet 6 inches
- D8 feet
Show answer & explanationAnswer & explanation
Correct answer: A. 5 feet
The Uniform Plumbing Code (UPC) specifies maximum developed lengths for common vents to ensure proper air circulation and prevent siphonage or backpressure in the drainage system. For fixtures like lavatories, the maximum developed length of the vent pipe from the trap weir to the vent connection is limited.
Why the other options are wrong
- B. This length is typically associated with trap arm lengths, not common vent developed lengths.
- C. This is too short and not a standard maximum length for common vents in this scenario.
- D. This length is generally too long for a common vent serving two lavatories, risking ineffective venting.
Common Vent Developed Length
The total length of a vent pipe, measured along the centerline, from the trap weir of the farthest fixture to the point where it connects to the vent stack or another vent pipe.
- Ensures adequate air supply to traps.
- Prevents siphonage and backpressure.
- Length limits vary by fixture and code.
Memory trick: Common Vents 'Keep Traps Breathing' within their limits.