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Discussion Starter · #1 ·
In the future, I will be adding a full basement bathroom (tub, toilet, sink) below an exising two-piece bathroom (toilet and sink).

I'll be working on the first and second story walls first, and I want to put any needed vent pipes in the first and second story walls now, since I'll have them open.

On the first floor, the sink is currently unvented (and is 5'6" feet from the toilet drain). Both the toilet and sink connect to a 4” cast iron drain line below the first floor, and which then drops to the concrete slab. Atop the drain line, a 2” iron pipe vent line runs to the roof through the first floor and second floor walls. The main stack for the house is about 18 feet away.

What type of vent pipes should I put in the walls now?

Can I combine the vents and drains for the two bathrooms in order to minimize roof pentrations and the number of slab penetrations?

I obviously have some flexibility in the design of the basement bathroom in terms of what goes where/distances, etc., so any advice is appreciated there too.

Thanks!
 

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A 2" vent will handle the new basement bathroom.
As for combining vents on multiple floors, you can but a vent is sized by what type of fixtures it serves as well as length of the vent used. But one roof penetration is possible
 

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Discussion Starter · #3 ·
If the basement is 7 DFU (sink 1 + toilet 4 + tub 2), and the 1st floor is 5 DFU (sink 1 + toilet 4), can I run a 2" pipe from the basement to the attic, then join the other 2" vent (the one from the 1st floor) in the attic, and have just one 2" pipe out the roof?

The total vertical height of the vent would be about 30 feet.

I believe the maximum is 16 DFU for a 2" vent.
 

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Vent

Yes you can combine in attic. For obvious reasons you can not run inline with first floor vent due to back gas. Connection in attic is the way to go. I am in the process of same project...
 

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Yes you can combine in attic. For obvious reasons you can not run inline with first floor vent due to back gas. Connection in attic is the way to go. I am in the process of same project...
Please explain the obvious to me.
What is run inline and back gas?
 
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