Bathroom DWV

I was hoping to get some feed back on a proposed bathroom layout and DWV. I've attached a sketch of the layout and an iso (you may have to rotate it to get the best view). Hopefully, it's not too much of a mess. The scale is not very good, but I just wanted to give you a rough idea. Basically, I wanted to back-vent everything except the guest shower in the common wall, then back vent the shower in the attic, then increase to a 3" pipe and vent through the roof. I wanted to do all of the vents in 2" so I don't have to mess with too many different pipe sizes. My main concerns are:

1. Is the double san-tee for the back-to-back guest lav and one of the master lavs the best way to do this?

2. Should the stack between the back-to-back lavs be 3" instead of 2". I don't think I have another 3" stack in the house and not enough elevation in the attic to put a 3" stack on the toilet and back vent the shower easily.

Thanks for looking at this.

If this is permitted for UPC

The double lav is a double fixture fitting. 2.0 X 1.5 x 1.5 x 1.5

When you roll the wye for the vent on the shower, make sure its above the flow line of the pipe.

Vents for the shower and lav can be 1.5"
Vents on the toilets can be 2"

Or you can just run vents in 2"

Thanks Terry. We're under the IPC down here, but the double fixture fitting looks like the best way to go. I had read somewhere that every house needed at lease one 3" vent through the roof, but I don't know if this is a code requirement or not, and I don't know if that means a continuous 3" vent, or if I could just use the pipe reducer in the attic. Is that a requirement, and would I need to change my bathroom DWV if I don't have any other 3" vents through the roof in my house?

UPC lets you use two 2" vents and one 1-1/2" vent.

I don't know what IPC uses.

vent

I do not know about the IPC because it is very lenient, but the usual requirement is that the aggregate area, not diameters, of the vents through the roof has to equal the area, not diameter, of the sewer into the building. If that applies to your area, then you would need additional vents besides that single 2" one. Why is the shower drain at one end? But even there, it might be within the distance to put the vent in the plumbing wall and run from there to the trap, avoiding the underfloor horizontal vent And connecting it back. Although if it were 2" and extended out through the roof vertically, AND you had a 1 1/2" vent for the kitchen, then they would satisfy the area requirement.

Thanks HJ. The scale on the the diagram is a bit off, but the shower drain will be off-center. I'll be using one of the Kerdi shower kits with an off-center drain and putting in a a shower seat along the common wall. The valve wall will be closest to the drain. I'll check on the IPC vent requirments, and taking that shower vent through the roof may be the best way to go.