Applicable venting for basement bathroom.

[Dgeist]

Hello, all. I'm in the process of planning the waste and vent paths for a new basement bathroom (lav, toilet, tub/shower). The home has two finished floors above the basement location, each containing an existing bathroom in a near vertical line going up. In planning the venting, I assume rules around wet venting would only allow using a portion of a vertical run from one of the upper floors as a wet vent if it were lav-ONLY, correct (i.e. no tub or toilet output in a wet vent)?

I'd like to avoid an air admittance valve, but also don't want to completely destroy my finished rooms above. Am I correct that I can't tie the vent for the basement into an existing vent (regardless of diameter) until I'm above the spill line on the HIGHEST fixture that drains to that stack? If I do end up having to run a vent all the way to the attic to egress the roof or tie into an existing penetration, are there any codes that would require more than 2"?

Thanks
Dan

 

[Terry]

Wet venting is only for the same floor, bathroom fixtures.
A waste stack from above does not count as a vent. Venting from below ties in at 6" above flood level of the fixture on the next floor, or through the roof.
2" would work fine as long as that is your local code. UPC allows 2".
Georgia IPC effective Statewide

 

[Sponsor]

 

[Dgeist]

Thanks for the clarification, Terry. I'm guessing that pic gets a lot of use on the forum.
You say "on the next floor" for vent tie in. In my home, each of the existing baths, lets call them "main floor" and "upstairs" has it's own discrete vent stack going all the way up to the attic and roof penetration. If I bring the vent stack from the basement fixtures up adjacent to the "main floor" bath vent, can I tie into that 6" above the highest fixture since none of the fixtures using THAT vent stack will overflow into the drain or does it need to go all the way up and tie in 6+" above the "upstairs" bath? to be above ALL the fixtures in the home. I'm pretty sure A and B are fine, but I'd really like to do C. I want to be sure about the theoretical before I start opening up bathroom walls to explore the actual.



Dan