Will use of an AAV on a shower arm allow more drop than the inside diameter of the pipe?

[240sxguy]

I have a situation where one bathroom is right above the other and the Ptrap for the upstairs shower hangs down really far into the lower bathroom. I want to move that Ptrap up and tight to the floor. Unfortunately this will create a drop roughly 3x the pipe ID and could cause trap siphoning. My shower arm already has an AAV installed about half way to the main drain/vent stack.

So, in this situation if I re-plumbed the drain and kept the AAV in place, would I be free to increase to a more dramatic drop after the AAV? I'm aware that WI has some unique rules but I wanted to do my homework on this one and find out what the generally accepted practices were.

Thank you!

 

[Terry]

Anything to drops below the venting can result in siphoning of the trap.
On the vertical, that's a santee fitting.

 

[Sponsor]

 

[wwhitney]

So, in this situation if I re-plumbed the drain and kept the AAV in place, would I be free to increase to a more dramatic drop after the AAV?

Not sure on the WI rules for AAVs, but yes, the AAV is your vent, so after the AAV, there's no restriction on the fixture drain's fall.

But the AAV has to be accessible and ventilated. Sounds like the AAV would be in the floor framing? You'd need a ventilated access cover for it.

Cheers, Wayne

 

[240sxguy]

Thanks Terry, that diagram helps.

Wayne - yes it's currently hidden (by the previous owner) and I will move it so it is accessible by a trap door. There's also adequate ventilation for it too. I did talk to a local guy who is a plumber briefly and he said AAVs are okay in Wi.

I appreciate the help!!