Section 918 of the International Plumbing Code describes the legal use of Air Admittance Valves as a means of venting a sanitary system.
918.3.2 states the following:
Stack-type air admittance valves shall be prohibited from serving as the vent terminal for vent
stacks or stack vents that serve drainage stacks having more than six branch intervals.
918.4 goes on to say:
Individual and branch-type air admittance valves shall be located not less than 4 inches (102 mm)
above the horizontal branch drain or fixture drain being vented. Stack-type air admittance valves shall
be located not less than 6 inches (152 mm) above the flood level rim of the highest fixture being
vented. The air admittance valve shall be located within the maximum developed length permitted for
the vent. The air admittance valve shall be installed not less than 6 inches (152 mm) above insulation
materials.
The way these sections are worded is confusing. Any advice? @Herin Reynold @simon
I think section 918.3.2 refers to limitations of AAVs used as a vent terminal for venting the stack itself more than six branch intervals while the 918.4 section talks about installing the stack type AAVs not less that 6 inches above the flood rim of the highest fixture being vented for systems that are less than 6 branch intervals. Definitely the way these sections are worded are confusing and also interpreting these sections are little tricky.