Fixing outdated basement bathroom in remodel

[Dwitting87]

Hi all,

I bought my house 6yrs ago. It was built in MI in the 1970s. I have (what I assume was) a roughed in bathroom in the basement with a toilet well, 2" stub coming out of the ground and a branch from a stack for a 1.5" for what I assume was a sink.

I've decided to look into making this a full bath, including a bath tub. My first thoughts going through this forum is that:

a. Why does it seem like all "roughed in" bathrooms don't have vent provisions?
b. I think I have too many fixtures unvented on this stack

Attached is what currently exists in my house and what I believe will resolve the venting issue. I believe it would be acceptable to have two wet vents--one for my kitchen sink and bathroom sink off my laundry basin, and another off my bathtub for my toilet. Any feedback would be appreciated. I'll be looking at what it takes to install a tub, but my first thoughts are on if I need to run another vent down to the basement (the obvious answer seems yes, I'm just concerned where makes the most sense). I've already resided to the fact that this project is probably going to require busting up the concrete to replace bad preliminary work.

 

[Dwitting87]

BTW this is a bit of a guess as to how things are running under the concrete. I think I'll have to bust it up to see what's really going on.

 

[Sponsor]

 

[Jadnashua]

In your second drawing, the only thing vented in the basement would be the shower. The line below the first floor's sink drain became a drain which cannot be used as a vent below it. Wet venting is only allowed within a bathroom group on the same floor. As shown, the toilet would siphon the sink.