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918.4 Location.

Individual and branch-type air admittance valves shall be located a minimum of 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.

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An AAV has to be above the flood level of the fixture it is connected to. These are all wrong, regardless of what code the dwelling falls under.

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.

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An AAV has to be above the flood level of the fixture it is connected to. These are all wrong, regardless of what code the dwelling falls under.

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.

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What does stack venting mean?

image12541.jpg

That doesn't look right. Vent stack and soil stack both begin at the building drain at the bottom and rise above the roof deck. The difference is that the individual drains branch off only from the soil stack and the individual vents branch off only from the vent stack.

I'm not saying the drawing is wrong, just that the terms used are in the wrong place.

Vent stacks are rare here. Mostly what we have are combination soil/vent stacks. They don't need to be separate here.

Marc

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