Island Sink AAV and Washer Branch in a Converted Apartment
A 24-year-old six-unit apartment building has four storeys, a 4-inch cast-iron soil stack, and a 2-inch galvanized water service. The owner converts the ground floor into a laundry and a small kitchenette. The contractor proposes two 2-inch PVC washing-machine standpipes connected to a single 2-inch horizontal branch that ties into the soil stack, plus a 1.5-inch island sink trap vented by an air-admittance valve (AAV) mounted inside the closed base cabinet. The contractor says no separate vent is needed because the AAV breathes and the branch is short. The building official rejects the plan, citing venting and trap-seal protection. The owner asks you, as the reviewing master plumber, to resolve the dispute without demolishing the new finishes. Site conditions: the island is 9 ft (2.7 m) from the nearest wall, the soil stack is 22 ft (6.7 m) from the washer branch, and the laundry has no floor drain.
1. Is the proposed AAV acceptable for the island sink? Explain the code tests and give at least two compliant alternatives if it is not.
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An AAV is not a universal substitute for a vent. It must be listed and sized for the fixture drain, installed above the trap arm, and accessible for inspection and replacement. Mounting it inside a closed base cabinet without an access panel fails the accessibility test. It also cannot be used where back-pressure or a positive-pressure condition can occur. For a 9 ft island, a 1.5-inch trap arm at 1/4 in/ft has a maximum developed length of about 6 ft, so the trap cannot reach a wall vent. Compliant options include: an island loop vent (foot vent) connected to a vent stack above the highest fixture, with the drain and vent arranged to protect the trap seal; an AAV listed for the application with a removable access panel and a vented cabinet; or relocating the sink to a wall. The reviewer should require a detail and a smoke test.
2. Evaluate the washer branch: fixture-unit load, venting, standpipe trap, and connection to the soil stack. What corrections are needed?
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Two washing machines at about 3 DFU each produce a small hydraulic load, so the 2-inch branch is not the main issue; venting and trap-arm distance govern. Each washer standpipe needs a 2-inch trap and an individual vent, or a common vent sized for the total load, taken off before the branch enters the soil stack. A 22 ft unvented trap arm far exceeds the 8 ft limit for a 2-inch trap arm, so the standpipes would siphon. The branch must connect to the stack at or above the fixture outlet level and must not be wet-vented through the lavatory. Add a 1.5-inch or 2-inch vent rising to the roof or tying to an existing vent at least 6 inches above the flood-level rim of the highest fixture. Also add a floor drain with a trap primer if the laundry is subject to flooding. Test with water and smoke.
3. What permits, inspections, and signatory requirements apply to this renovation?
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Work requires a plumbing permit and approved plans before installation; the contractor cannot legalize it afterward. The master plumber of record signs and seals the plans and the application, and only a licensed master plumber may supervise the plumbing work. Required inspections include rough-in before covering, vent and trap-seal inspection, water supply pressure test, DWV water or air test, and final inspection. The building official may require as-built drawings for the unpermitted work. The owner should be advised in writing that approval of the AAV and washer vent corrections is conditional. A certificate of occupancy should not be requested until the final inspection passes.