I just bought a house with an unfinished second floor. The bathroom has a 3" soil stack roughed in and stubbed, but thats it. The first floor stack vent is closeby, so theres no problem continuing the second floor stack to meet the venting the first floor stack.

The problem is that the soil stack is in the left hand corner of the room. I want to put the toilet in the right hand corner which would be 6'6" from the stack, and tie the sink and shower into the toilet drain line in between the toilet and stack. I will dry vent both the shower and sink.

Stack... toilet
O ----o----o---- O
... |... |
... |... |
... vent... vent
... |... |
... shower.. sink


Since the toilet is more than 6 feet from the stack (albeit only 6"), do I really need another vent for the toilet, and where would I put it? Or should I just give up the 6" and have a smaller sink cabinet?

Sorry Steve,

Your diagram may be real simple for you since you have it all in your minds eye but it's all greek to me. Let me show you a simpler way.
Toilets 3" drain to stack. The lavatory to connect to the toilet drain and run out the roof or revent back to existing dry vent and the shower to connect to the lavatory vent and be wet vented by it as will the toilet. Sound like a plan? Cheers, tom

I may not have my terminology correct. The 3" pipe that is stubbed drains into a branch that drains to the sewer. That existing drain also serves all the first floor fixtures and goes to a 3" vent out to the roof. So the second floor stub is parallel to the existing 3" vent and about 4' away, and drains almost directly to the sewer (its the lowest branch).

So, according to your response, is it true that I dont need to T the 3" stub so that in connects to the second floor drain and to the existing 3" vent? Instead I can just connect the new toilet drain to this stub, connect the lav and shower to this toilet drain and vent through the lavatory vent? Does this vent serve as the toilet vent was well?

Hey Steve,
What do you mean by, "The bathroom has a 3" soil stack roughed in and stubbed,"
The bath has a 3" dry vent that's stubbed up and capped? The bath has a 3 inch stub up roughed for a toilet and connects back into the main sewer?
I think you meant the first one but I want to be sure. The term, "roughed in" threw me.
Assuming that you have a 3" dry vent that's been capped off.

" is it true that I don't need to T the 3" stub so that in connects to the second floor drain and to the existing 3" vent?"
Now I'm confused again. Is the "second drain" the first floor stack vent"
If it is you can not connect the bathroom group to it and use the capped off stack for a vent. That would be discharging a major fixture past a unvented minor one. The minute you run a discharge into a vent stack it becomes a stack vent.
So what are we left with? If the 3" pipe is dry down to the main and has no first floor fixtures draining or venting into it you may connect the toilet drain to the stubup. It is now a stack vent drom the connection down and a vent stack from the connection up. The lavatory drain will connect to the toilet drain and be revented back to the vent stack,( which in turn can be revented back in the attic to the existing roof vent). The shower will connect to the lavatory drain line and be wet vented by it as will the toilet.

I hope I didn't confuse you with the terms stack vent and vent stack. It's simple. Stack vent= a vertical pipe that carries discharge. Vent stack= a vertical pipe that's dry and acts as a vent. So a pipe can be a stack vent up to the last fixture that discharges into it but from there on through the roof it morphs into a vent stack. Did I confuse you farther? Regards, Tom

Its getting clearer! The stub must be a 'stack vent' as it goes directly from the second floor to the sewer without any intervening fixtures. So if I put a sanitary T on the stub, connect the T to the toilet drain to the toilet flange, and extend the pipe up through the roof (or connect it to the existing roof vent), the vertical pipe becomes the "vent stack".

Now I connect the lav drain to the toilet drain and vent the lav to the vent stack I just added.

There's still two things I'm not clear on. 1) The shower is opposite the lav, so I can't drain it into the lav drain (the toilet drain is in between the lav and the shower). So, can I also drain the shower directly into the toilet drain and have a separate dry vent for the shower (its about 4' from the toilet drain, and 5' from the lav drain). 2) the distance between the stack and the toilet flange is 6'6" measuring from the closest rim distances - doesnt this violate code for having tha maximum wet vent distance for a 3" pipe? Or does the lav vent act as a dry vent for the toilet?

Hey Steve,

"Its getting clearer! The stub must be a 'stack vent' as it goes directly from the second floor to the sewer without any intervening fixtures. So if I put a sanitary T on the stub, connect the T to the toilet drain to the toilet flange, and extend the pipe up thru the roof (or connect it to the existing roof vent), the vertical pipe becomes the "vent stack"." You got it!!

"Now I connect the lav drain to the toilet drain and vent the lav to the vent stack I just added." Right!

"can I also drain the shower directly into the toilet drain and have a separate dry vent for the shower?"

Yes,but since this will be a dry vent that is not washed by a fixture the fitting that you take off for the vent will have to be rolled up on a 45 degree angle. The reason for this is that vent such as the lav vent's washed and scoured by the lavs drainage while the if the shower vent fitting were flat crud could build up in the opening and block the vent. If the fitting's rolled up the crud drains on by and doesn't enter then vent fitting.
Don't blaime me, it's code! The toilet will be wet vented by both vents.

Good luck, Tom

Thanks a lot, tom, and I appreciate your patience with me... I've also read many of your other responses - you're extremely helpful.