Adding 2nd toilet 8' from main stack

[Andrew Schrader]

Hello everyone,

I'm adding a second toilet to my home (up/ down duplex if that matters). For my side, the upstairs, I currently have 1 bathroom. The current toilet is 1'-2' from the main stack. I want to add a second toilet in my laundry room that adjoins the bathroom. The new toilet closet flange would be ~8' from the main stack.

Per UPC (MT follows UPC) I should add a 1-1/2" vent for 3" drain or I can run a 4" drain without a vent. Per IPC I can run a 3" drain from the W.C. to the main stack without a drain. If I run a 4" (or even a 3") drain will there be any issues with one toilet draining the other bowl? Since the current toilet is so close to the stack I assume it'll work.

I plan to replace some of the current toilet's drain piping and use a combo wye to connect the new toilet & the current toilet. The new toilet is coming from where I was sitting while taking the picture. Since the new toilet is ~30" horizontally over from the stack, would it be better to do 2 rolled 45s with a steeper section in between, or to drop the ~6-12" elevation vertically and keep the rest of the piping at 1/4" per ft slope?

Thanks,
Andrew

 

[Andrew Schrader]

Thanks in advance for your time viewing and any comments.

 

[Sponsor]

 

[wwhitney]

Per UPC (MT follows UPC) I should add a 1-1/2" vent for 3" drain or I can run a 4" drain without a vent.

That's contrary to my understanding of the UPC, do you have a reference for that? I understand every toilet to require a 2" vent taken off within 6' of developed length, under the UPC.

Cheers, Wayne

 

[Andrew Schrader]

@wwhitney I guess I interpreted / assumed that based on if the main 4" stack vent was within the required 10' from the water closet. Since I would be 8' from the main stack, if I were to run a 4" drain then it wouldn't require an additional vent. But I could have been mistaken.

 

[wwhitney]

Up.codes doesn't have Montana's version of the UPC, but it has California's, and I don't think they've amended the relevant section:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/10/traps-and-interceptors#1002.2

Note 2 to the table says the WC vent has to be taken off within 6'.

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#703.2

And this table says a 1-1/2" vent is good for 8 DFUs, but then note 3 says "except for six-unit traps or water closets". So you need at least 2".

The UPC does allow wet venting within a single bathroom group, so depending on what else is with the toilet and how the drainage and vents are connected, you could wet vent the toilet. But as the stack is venting the existing toilet, I don't think you can combine the existing toilet drain with any other drain before the stack.

Cheers, Wayne

 

[Andrew Schrader]

@wwhitney
It'll just be a water closet & a utility sink using that 3" drain line. So I'll vent it with a 2" pipe.

I plan to connect them at the connection on the main stack. The new & current water closets drains will run together for the length of a long sweep combo, <1', probably <6" before dumping into the stack.

Thanks Wayne

 

[wwhitney]

I plan to connect them at the connection on the main stack. The new & current water closets drains will run together for the length of a long sweep combo, <1', probably <6" before dumping into the stack.

I think that 6" - 12" is a technical violation, and what you're supposed to do is use separate entries to the stack--either stacked sanitary tees, or a double combo fitting. Or else take a vent off the existing toilet line before you combine it with the new toilet line.

On the other hand, I believe it would work fine. Depending on how the new toilet line is run, the IPC would consider it acceptable to wet vent the existing toilet via the new toilet.

Cheers, Wayne