I am in the process of installing a full bathroom in my basement. The basement is not roughed in so I have to break up the floor slab first. My question is about drain/venting. I have attached my floor plan, I need to know where I should place my vent? Or vents?

Can I place a single vent in back of my LAV in the stud wall that will serve as the vent for all three fixtures?

Thank you.

If you keep the present configuration you will have to run a separate vent for the shower. As it stands now the shower's unvented.
To avoid running a separate shower vent you will have to move fixtures or figure a way to tie the shower drain to the lavatory drain where it will be wet vented. Good luck, Tom

How about if I move the vent to a location between the shower and the w/c?

Or, can I run a vent at the shower a few feet above the floor slab, then run horizontal over to the sink vent and tie in?

See the elevation view diagram attached to supplement my last post.

"How about if I move the vent to a location between the shower and the w/c?"
Then you would be installing a "S" trap on the lavatory. Another no-no.

"can I run a vent at the shower a few feet above the floor slab, then run horizontal over to the sink vent and tie in?"

Why run the vent over the floor line? Since the slab will be torn up anyhow keep it under the slab.
Roll a combination wye and eighth bend up om a 45 degree angle,(this's important) after the trap and take the vent over to the wall. Come up in the wall and revent over to the lavatory vent. You may then take the lavatory vent out the roof of revent back into a existing dry vent in the attic. Good lucki, Tom

I guess I should have said that I already have part of the slab torn out. My original plan was to have only a sink and w/c. Then, after the floor demo, I decided to add the shower. That's not to say I can't do more demo, but I would rather not. I'm attaching another sketch showing the current state of my floor demo.


"Why run the vent over the floor line? Since the slab will be torn up anyhow keep it under the slab."

If I do decide to run the shower vent above the slab, would it be acceptable? It just seems easier than tearing out more concrete.

Break up a little bit more and do the job right. Regards, Tom