Mechanicals · definition
A one-way vent valve allowing air in without a roof penetration, useful for islands and additions where running a vent is impractical (where code permits).
Source: Oatey — Understanding Air Admittance Valves
Where this term lands on a Columbus budget
The cost pages carry the current local ranges, and the guides explain what moves them. A published range becomes a project number only after someone looks at the site.