A plumber is designing the venting system for a battery of three lavatories in a commercial washroom. Each lavatory has a 1.25-inch trap arm and is located within 0.75 metres of the proposed soil stack. To optimize material usage and minimize penetrations, which of the following venting arrangements, where permitted by local authority, would be the most efficient while still providing adequate venting for all three fixtures?

Question: A plumber is designing the venting system for a battery of three lavatories in a commercial washroom. Each lavatory has a 1.25-inch trap arm and is located within 0.75 metres of the proposed soil stack. To optimize material usage and minimize penetrations, which of the following venting arrangements, where permitted by local authority, would be the most efficient while still providing adequate venting for all three fixtures?

Answer options:

• Individual vents for each lavatory.
• Wet vent all three lavatories through the branch drain.
• Use a common vent for the two end lavatories and an individual vent for the middle one. ✅ Use a circuit vent for all three lavatories, connecting into the branch drain after the last fixture.

Correct answer: Use a circuit vent for all three lavatories, connecting into the branch drain after the last fixture.

Explanation: A circuit vent is an efficient method for venting a battery of fixtures (fixtures installed on a common horizontal branch drain) and would be appropriate here. The circuit vent connects to the branch drain immediately downstream of the most downstream fixture and rises to connect to the vent stack or another approved vent, thereby serving all fixtures on that branch. Individual vents would use more material, while wet venting multiple lavatories directly may not always be permitted or practical for this configuration, and a common vent for only two of three would be inefficient.