Which vent rises as near as possible to or above the highest water level in the fixture vented before connecting to the stack or main vent?

Which vent rises as near as possible to or above the highest water level in the fixture vented before connecting to the stack or main vent?

• A. Wet Vent
• B. Roof Vent
• C. Island Fixture Vent
• D. Individual Vent

Answer: (C)

When venting a fixture that sits on an island, the vent must rise through the island and extend to a level at or above the highest water level (flood level rim) of the fixtures it serves before it connects to the stack or main vent. This ensures the vent remains above the water surface as drainage occurs, providing a clear air path and preventing siphon that could pull water from traps. An island fixture lacks a nearby wall vent, so the dedicated island vent must be designed to rise high enough to serve the fixtures before joining the building’s main vent system.

When venting a fixture that sits on an island, the vent must rise through the island and extend to a level at or above the highest water level (flood level rim) of the fixtures it serves before it connects to the stack or main vent. This ensures the vent remains above the water surface as drainage occurs, providing a clear air path and preventing siphon that could pull water from traps. An island fixture lacks a nearby wall vent, so the dedicated island vent must be designed to rise high enough to serve the fixtures before joining the building’s main vent system.