Bathroom addition

I would like to add a 1st. floor full bathroom. We have a powder room on the 1st floor, but need a full bath for my elderly mother. The location of this new bath is almost right below a full bath on the second floor. The soil stack from the second floor bath ties into the waste drain (3" PVC) approximately 8ft. from where the new toilet would be located. We will also have a shower stall and a vanity sink as well. My question is does this new bath installation need a new vent run, or would the soil stack from the second floor serve as the vent?
Thanks

Yes it needs a new vent. Now, that vent line doesn't need to go all the way up through the roof, but you must attach it 42" (or higher) above the floor (or 6" above the flood rim of the highest drain, whichever is higher). You could connect it in that attic.

bathroom

You need a new vent system. The upstairs bathroom complicates your installation, it does not make it easier.

Studor vents

If they are code in your area, you could use studor vents. A studor vent is device that allows air into the line when there is a vacuum (like from water falling down a pipe). Otherwise, it remains closed so that sewer gas cannot get through. They are allowed by code in some places and can save a lot of wall opening and piping for bathroom additions in basements and first floors. To learn more, google 'Oatey Sure Vent' or just 'studor vent'.

seattleplumber said:

If they are code in your area, you could use studor vents. A studor vent is device that allows air into the line when there is a vacuum (like from water falling down a pipe). Otherwise, it remains closed so that sewer gas cannot get through. They are allowed by code in some places and can save a lot of wall opening and piping for bathroom additions in basements and first floors. To learn more, google 'Oatey Sure Vent' or just 'studor vent'.

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Studor Vents, Shure Vents, and AAV's are not allowed in all areas. They are used by lazy plumbers, and on jobs where the GC's are tightwads. They originally wer used a lot on the plumbing on tin houses on wheels. Lately they have been making their way into multi million dollar home while trailer manufacturers have started shying away from them. It's funny how the people buying trailers don't want them because of the smells and noises they make... Go Figure!

Redwood said:

They are used by lazy plumbers

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I kind of resent that comment. But agree with the Contractor one.

Here in Florida they are used everywhere. I personally would rather see contractors have to make plumbing chases and 2x6 walls everywhere plumbing is located, but thats not going to happen. The building codes also dictate what we have to do here when it comes to location of vents thanks to the hurricanes. If was was up to me we would be back to cast iron, lead and oakum joints and copper , but that not going to happen either.

To answer your question bigguy, you will need to have a vent for that bathroom group.