Basement bathroom venting question

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I have roughed in *most* of what we should need for a basement bathroom. However, I am having issues understanding what I need from a venting perspective.

We do not have easy access to a main vent stack. Unless we want to rip out walls and vent all the way up through the roof (obviously a last resort), I believe I am left with two options:

1. AAV (may not be code, but....) or
2. Wet vent into an undersized vent (2 inches)
3. Both?

I've included a simple diagram below... any questions, thoughts, critiques, etc., would be very welcome!!!

basement bathroom venting.png


In the Trades
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Berkeley, CA
If the 2" pipe coming off shower fixture drain (i.e. to the right of the WC in your drawing) were all vertical, and you used an AAV on it, that would dry vent the shower, and the shower would wet vent the WC. The lav is dry vented via its AAV.

However, you can't have a horizontal dry vent underneath the floor, So you either need to reroute the the shower drain so that it can pass under or right next to a wall so that the dry vent can come off vertically (or you could instead do that for the WC drain), or you need to change the order of fixture connections so that the sink can wet vent the shower. I.e. make the sink one of the two upstream most fixtures.

Regardless, your shower trap arm, which extends from the trap to either the dry vent takeoff, or the wye where a dry vented drain comes in to wet vent the shower, is limited to 2" of fall, which means at most 8' of length if you get a perfect 1/4" per foot of fall.

Cheers, Wayne
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