Need help with venting for basement bathroom

[Scott Wilton]

I have a house with an existing basement full bathroom that has also been roughed out for another full bath (with a shower). I want to build out this second bath. For this second bath I don’t know exactly what’s under the concrete but there’s a toilet drain coming to the surface of the concrete, a 2 inch drain pipe in a 2x4 “box” in the concrete so you can add a p-trap and hook up a shower, and a 2 inch drain/vent pipe coming vertically out of the floor where an unfinished wall is for the sink/vent. The other existing bath is downstream from this potential new bath.

The shower drain for this new bath is the farthest fixture in both the new bath group and the whole basement, then comes the toilet 5 feet away (will be 6 feet with the trap for the shower) and the 2 inch drain/vent is 2 feet from the toilet connection and appears to be downstream from the toilet though I’m not sure of that.

The basement has a separate and apparently dry 2 inch vent that runs horizontally near the basement ceiling that I can connect this new bath venting to, which I plan to do.

I have reviewed a lot of threads about wet vents etc. but some of the rules are confusing and I need some help. My question is whether I need to add a separate vent for the shower. I can break up some of the concrete and run some pipe for a vent in a wall I will build about a foot or two away from the shower drain, but would rather save the time if I don’t need to. My understanding is that the toilet sharing the lavatory drain/vent is fine, but I’m unclear about the shower.

Please let me know if I need to add a shower vent, and make any other comments if I’m missing something else. This venting stuff can be complicated. Thanks.

 

[PlumbNuts]

I do not like making assumptions but in this case I will assume that the basement underslab rough-in was done during original construction by the plumbing contractor.
If this is an accurate assumption then the drainage and vent requirements were considered by them and already approved.
Your lavatory will provide the proper wet venting for your bathroom addition, just extend your vent to the exisitng vent.
Best wishes to you, keep us posted.

 

[Sponsor]

 

[Scott Wilton]

I do not like making assumptions but in this case I will assume that the basement underslab rough-in was done during original construction by the plumbing contractor.
If this is an accurate assumption then the drainage and vent requirements were considered by them and already approved.
Your lavatory will provide the proper wet venting for your bathroom addition, just extend your vent to the exisitng vent.
Best wishes to you, keep us posted.

Thanks for the reply.

Yes, it was approved and actually has a sticker from the inspector on the vent/drain. I wasn’t sure that this means the vent system was approved, but I guess you’re right that they would have asked the plumbing contractor to do a vent for the shower if it wasn’t sufficient. I just don’t want to finish everything and find out that the shower trap is siphoning or something. Again these venting issues seem complex sometimes and if I need to do something now is the time.