Journeyman Plumber ExamFixtures, Faucets, and Other AppliancesMedium
A client wants to install a new kitchen island sink. Due to the island's location, it is impossible to run a conventional vent pipe directly up through the roof or connect to a nearby vertical vent stack. Which of the following alternative venting methods is generally accepted by plumbing codes (e.g., UPC/IPC) for an island fixture?
- AAn air admittance valve (AAV) installed directly under the sink in the cabinet.
- BAn island fixture vent (loop vent) installed to connect to a branch vent above the flood level rim.
- CA circuit vent connecting the island sink to the main building drain.
- DA common vent shared with a nearby bathroom group via a horizontal pipe below the flood rim.
Show answer & explanationAnswer & explanation
Correct answer: B. An island fixture vent (loop vent) installed to connect to a branch vent above the flood level rim.
For island sinks where traditional venting is impractical, an island fixture vent (also known as a loop vent or Chicago loop) is the most common and code-approved alternative. It provides the necessary air circulation by looping the vent pipe up above the fixture's flood level rim and then back down to connect to a branch vent or stack.
Why the other options are wrong
- A. While AAVs are permitted in some jurisdictions and specific situations, they are often considered a secondary option to a full island loop vent, and their use can be subject to local amendments and limitations, making the loop vent a more universally accepted 'generally accepted' method.
- C. A circuit vent is used for multiple fixtures on a horizontal branch, not typically for a single island sink, and often requires specific conditions for its application.
- D. Connecting a common vent horizontally below the flood rim would create a potential cross-connection and is not a valid venting method.
Island Fixture Vent (Loop Vent)
A specialized venting arrangement for island sinks that cannot be conventionally vented, involving a vent pipe that rises above the fixture's flood level rim before connecting to a branch vent.
- Also known as a loop vent or Chicago loop.
- Ensures adequate air supply to prevent trap siphonage.
- Requires the vent portion to rise above the flood level rim of the fixture.
Memory trick: Island sink's vent, a loop it must bend, to keep the air flowing 'til the very end.