What is used as an island vent alternative method?

• A. Air admittance valve
• B. Roof vent
• C. Direct vent
• D. Fan vent

Answer: (A)

When an island sink can’t be vented through a wall or roof, an air admittance valve provides a practical venting option. This device acts as a one-way valve that opens to admit air into the drainage system when negative pressure occurs as water drains, preventing the trap from siphoning. Once pressure equalizes, the valve closes to block sewer gases from escaping. That makes it well suited for an island installation, where traditional vertical vent piping isn’t feasible. Just keep in mind that it must be installed in accordance with local codes (accessible for service, placed on the trap vent arm, and located in a permitted spot) and is not a substitute for all venting scenarios in every building. The other options—roof vent, direct vent, or fan vent—are not used to vent an island sink in the same way, so they don’t fit this specific application.