Air Admittance Valve Installation Check (IPC 918)
The AAV is sold as the thing that saves you a vent through the roof, and IPC 918.7 says plainly that it does not: at least one vent pipe must still extend to the OUTDOORS. A valve admits air to relieve NEGATIVE pressure and does nothing about POSITIVE pressure -- the air a discharging stack pushes ahead of it needs a path out, and a building vented entirely on valves has none. No amount of correct placement fixes that. The rest is placement and capacity: not less than 4 in above the branch or fixture drain served (918.4), not less than 6 in above insulation (918.6), in a VENTILATED space, ACCESSIBLE because a diaphragm eventually fails, and rated in DFU per its ASSE 1051 or 1050 listing (individual, branch, and stack types are not interchangeable). Whether AAVs are permitted at all is the first question and varies by jurisdiction.
Formula and source
pass requires an outdoor vent present, a ventilated space, accessibility, height above the branch or fixture drain >= 4 in, height above insulation >= 6 in where insulation is present, and a valve DFU rating >= the DFU served where both are entered.
IPC 918 - air admittance valves located not less than 4 in above the horizontal branch drain or fixture drain being vented (918.4), installed not less than 6 in above insulation materials (918.6), located in a ventilated space and remaining accessible, and at least one vent pipe extending to the outdoors even where air admittance valves are used (918.7).
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