to the exterior of the structure. Stack vents and vent stacks are permitted to terminate to a stack–type air admittance valve. The exception is for stack vents or vent stacks that serve drainage stacks exceeding six branch intervals.Because the AAV will not provide relief of positive pressures, there are certain installation requirements that are specified in the IPC to relieve positive pressure. The one open pipe vent required on every building drainage system in Section 918.7, Vent Required, and Section 903.1, Roof Extension, mandates that at least one vent pipe shall extend to the outdoors to relieve the system’s positive pressure. Section 918.3.1 contains measures for pressure relief by requiring the installation of a relief vent where the horizontal branch is located more than four branch intervals from the top of the stack.American Society of Sanitary Engineers (ASSE) has recently developed ANSI/ASSE Standard 1049﹘Performance Requirements for Individual and Branch Type Air Admittance Valves for Chemical Waste Systems.Air Admittance Valves (AAV) that are in compliance with ANSI/ASSE 1049 and meet the requirements of Section 702.5 and tested to ASTM F1412 for chemical resistance are now allowed to serve as the vent for non-neutralized special waste systems as an option to chemical waste vent piping terminating outdoors. It is quite common to see laboratory sinks that receive chemical waste located in islands in the Air Admittance—Individual VentAir admittance valve closes and seals under zero or positive pressuresStudor ChemVent Air Admittance Valve (Courtesy of IPS )Methods of Venting Plumbing Fixtures and Traps in the 2018 IPC 7
middle of rooms. To vent the system for these sinks using vent piping that can only terminate outdoors requires extensive labor and material. The use of the AAV’s will significantly reduce the cost of plumbing these laboratories.Air admittance valves shall not be located in spaces utilized as supply or return air plenums. In these locations, the negative or positive pressure conditions could adversely affect the valves operation. Air admittance valves without an engineered design shall not be utilized to vent sumps or tanks of any type. The illustration below shows an example of one manufacturer’s engineered design for use of an air admittance valve on a sump. This design allows for positive pressure relief.Air admittance valves shall not be installed on outdoor vent terminals for the sole purpose of reducing clearances to gravity air intakes or mechanical intakes.The installation of air admittance valves must conform to the requirements of Section 918.3 through 918.8 and the manufacturer’s instructions. Where differences occur between the provisions of the code and the manufacturer’s instructions, the most restrictive provisions must be applied.