Vent Termination Too Close to an Operable Window
During a rough-in inspection of a two-story single-family house, the inspector finds a 2-inch vent stack serving a second-floor bathroom group terminating through the roof. The roof penetration is 3 ft from an operable bedroom window on the same roof plane, and the vent terminates 6 inches above the roof surface. The roof has a 4:12 slope. The vent also passes within 4 ft of a fresh-air intake for the HVAC system located on the same roof. The plumbing contractor argues that because the vent goes through the roof, it is compliant. The bathroom group includes a water closet, lavatory, and bathtub, all on a 3-inch building drain. The inspector must decide whether to approve, fail, or require correction.
1. Evaluate the vent termination location against typical code requirements and state the correction needed.
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Vent terminals must be located a minimum distance from operable windows, doors, and air intakes - commonly 10 ft horizontally, or 2 ft above the window if within that distance, and at least 3 ft above or 10 ft horizontally from a forced-air intake. Here the vent is 3 ft from an operable window and 4 ft from the HVAC intake, both inside the prohibited zone. Terminating 6 inches above the roof is also generally insufficient; the code typically requires the vent to extend at least 6 inches above the roof but not less than 12 inches above the roof surface for a slope up to a certain pitch, and more above snow line. The correction is to relocate the vent so it is at least 10 ft from the window and intake, or raise it to the required height above the window if the horizontal distance cannot be achieved, and extend it to the proper height above the roof. Passing it because it penetrates the roof is wrong - penetration does not cure a proximity violation.
2. The contractor proposes adding an air admittance valve inside the wall instead of relocating the roof vent. Assess this proposal.
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An air admittance valve is not a substitute for a required vent terminal in this situation. AAVs admit air to balance pressure but do not relieve positive pressure or serve as a termination for a stack that must vent to atmosphere, and they are generally limited to individual or branch venting of fixtures, not to replacing a stack vent that also serves as the building's main vent. Using an AAV here would leave the stack without a proper atmospheric termination and would not resolve the window or intake clearance issue. The correct path is to relocate or extend the roof termination. Also verify that the AAV, if used elsewhere, is installed in an accessible location with the required minimum height above the fixture and within the manufacturer's listing, and that the local code even permits AAVs.