It is my desire to install a sink, toilet and small shower in my basement. Nothing is currently “stubbed” in. My question concerns the Drain/Waste/Vent system requirements associated with this project. In the area of the basement where I want to put this bathroom, I have a 4” vertical waste/drain pipe running down below my basement floor. One floor up from the basement, I have a toilet that (I think) drains directly into this waste/drain pipe. I do not see any separate vent pipe from this toilet. I think (not 100% sure) that this waste/drain pipe is tied into the vent system that runs up through the attic and out through the roof (I think they call this “wet venting?). I will cut through the concrete floor and tie the sink, toilet and shower to the drain line running under the basement floor. The drain line running under the concrete floor is tied to the 4” vertical waste/drain pipe referenced above. Do I need to add a separate vent system for the sink, toilet and shower? If I do, I think the project will be nixed because running a separate vent line from the basement up approximate four levels and through the roof would require massive demolition and repair.

Most bathroom groups are roughed in like this.
Toilet connects to sewer main. The toilet wet vents through the lavatory vent. Lavatory connects to toilet drain and runs a vent out the roof or revents back into a dry vent in the attic off the top the stubout tee. The shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes but also The Standard Plumbing Code Book.

You ask, "Do I need to add a separate vent system for the sink, toilet and shower?"
No, you do not need to vent each fixtures separately unless lolcal codes mandate it. But you will have to vent the basement group. What you can do, if local codes allow, is to install a AAV,(Air Admittance Vent, see image) on the lavatory to serve as a vent for your group. Good luck, Tom

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Originally Posted by speedball1

Most bathroom groups are roughed in like this.
Toilet connects to sewer main. The toilet wet vents through the lavatory vent. Lavatory connects to toilet drain and runs a vent out the roof or revents back into a dry vent in the attic off the top the stubout tee. The shower connects to the lavatory drain and is wet vented by it. This is a normal rough in and is acceptable both by local and state codes but also The Standard Plumbing Code Book.

You ask, "Do I need to add a separate vent system for the sink, toilet and shower?"
No, you do not need to vent each fixtures separately unless lolcal codes mandate it. But you will have to vent the basement group. What you can do, if local codes allow, is to install a AAV,(Air Admittance Vent, see image) on the lavatory to serve as a vent for your group. Good luck, Tom

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Tom,

Thanks for the feedback but I am still confused (dumb in reality on plumbing issues of this sort). Not sure what you mean by 'lavatory vent" or "lavatory" or "lavatory drain"? Is the definition of "lavatory" the shower drain and the sink drain? I apoligize for the question "Do I need to add a separate vent system for the sink, toilet and shower?" it was not worded correctly. I meant to say "Do I need to tie the sink, toilet and shower vent pipes together and run this vent pipe up through the roof"? You suggested that I vent the sink, toilet and shower "group" using a AAV. Do you know where I would install this? (above the basement floor?) and would I tie this to the 4" vertical stack? Any advice would be helpful and again, thanks for the feedback.

Go back and read my post. Study how the typical bathroom group is roughed in. One vent off the lavatory will service the entire group. This will be installed on the tee that the lavatory stub-out comes out of. A lavatory is a bathroom sink. Regards, Tom

A long time ago plumbers installed over sized waste pipeing so that they would take the load of waste and rain water from roofs as well.
The point is if your connecting on to a 4" pipe u don't need a aav.
the aav might make noise or even over flow if the drain is cloged.
but u will need a 4" backwater valve at the start of your project

Snake, you are out of your comfort zone. Your advice was not good, neither was it practical, neither is it legal.