Around here 'A' Rated AAVs are permitted below the rim but must be 6" above the trap. Bill, I never heard of an A rated AAV. Is that an official designation? I thought that AAVs are AAVs and mechanical vents are not. Mechanical vents are only approved for manufactured homes and RVs. I'm specifically referring to AAVs, not mechanical vents for mobile homes. Quality AAVs for branch drains or fixture drains are not required to terminate above the flood rim. Only stack AAVs need to be above the flood level rim of the highest fixture being vented.