Vents and Venting
Vents and Venting tests the venting system that protects trap seals: vent types, sizing, wet venting, air admittance valves, and terminal locations. P1 questions often ask whether a vent is properly sized and whether its termination is high enough and far enough from openings.
Vent terminal height
Under IPC 903.1, an open vent terminal must extend not less than 6 inches above the roof. Where the roof is used for any purpose other than weatherproofing, the vent must extend not less than 7 feet above the roof. Terminals must also be located away from windows, doors, and property lines as required by the code.
Vent sizing and wet venting
Vent size is based on drainage fixture units and the length of the vent. A vent must be sized for the fixture units it serves. Wet venting is permitted for bathroom groups under specific conditions, with the wet-vented portion sized to carry both drainage and venting. A vent cannot serve as a drain.
Air admittance valves
Air admittance valves admit air but do not release sewer gas. They must be accessible, installed in the correct orientation, and used only where the code permits. They do not replace a required vent terminal where one is mandated.
Worked example
A vent terminates 4 inches above a flat roof that workers use for maintenance. The 4-inch height fails both rules: it is below the 6-inch minimum and far below the 7-foot requirement for a roof used for purposes other than weatherproofing. The vent must be extended to at least 7 feet.
Traps that cost marks
Candidates forget the 7-foot rule for usable roofs. They also overlook wet-vent sizing limits, install an AAV where it is inaccessible, or use a vent pipe as a drain.