Routing vent under slab?

[JeffeVerde]

How do vent lines get run under a slab? It's my understanding that a vent has to slope a minimum of 45º until it's 6" above the flood line, but I'm not sure how to achieve that with underslab lines.

I'm planning a large walk-in shower, and the wall I'll vent up is the opposite direction from the waste line. The depth of the main waste line (2' below top of slab) doesn't allow for a 45º run back to the venting wall, and the only way to route the waste under the vent wall would be to make a 180º loop from the shower drain to the wall, and back to the main waste in the middle of the room. The shower drain is 2' in from the vent wall, and the main waste is 2' in the opposite direction. I *think* I've got enough rise/run that I could rotate the vent wye up and put a 1/6-bend at the vent wall.

 

[JeffeVerde]

I think I figured it out. Run the waste line all the way to the vent wall, sweep up, sani-T back into the room to the shower drain/trap, and the vent continues up the wall - like this?

There's a tub planned further upstream on the main waste line. Could the shower vent supply the tub as well? That would save me a footing penetration (this is all on slab). The shower branch is 4' long, and it would be another 4' up the main 4" waste to the tub drain -- or I could branch off the shower branch and bring that down to 7' total, from tub drain to vent stack. ------ If the branch length is an issue on sharing the vent, there's a bench seat in the shower, halfway between the tub and shower drains. If I brought my vent stack up there, it would be 3' to the tub drain and 3' to the shower drain.

 

[Sponsor]

 

[hj]

drains

What you show is how I would do it, with the modification of using a "back to back fixture fitting" instead of the tee and run from it to the shower and tub.

 

[JeffeVerde]

What you show is how I would do it, with the modification of using a "back to back fixture fitting" instead of the tee and run from it to the shower and tub.

Where would the back-to-back go? This is slab-on-grade, so everything's "flat" (except for the drain pitch). To add to the fun, the tub is in a bump-out with 15"x18" footings on 3 sides, and the tub and shower are on different wall planes. Here's a plan view. The heavy black line is the existing 4" waste - everything below that is future construction. The thinner black lines are my proposed layout

 

[JeffeVerde]

Went with this layout. Immediately after the combi to the shower, I placed a street-45. This avoids a horizontal vent, and brings my vent thru the floor under the shower bench. When the wall's framed, I'll 45 into the wall to complete my vent to roof.

Inspector's happy, pressure test passed, Underground Soil-pipe sign off done. On to concrete

Thanks, all, for your input.

 

[hj]

Dwv

Our inspectors would NOT have been happy with the shower drain flowing past the tub connection. Your plumbing may have been "flat", (actually almost all plumbing is flat), but it should have been at least 15" deep. The double fitting would have been under the seat, (it could even be installed on a 45 if depth was a consideration), and the vent offset above the floor under the seat.