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Two toilets...one vent??

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carlspackler

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Discussion starter · #1 ·
I had a plumber come in to estimate some work I need done for a remodel. What I have is a toilet on the top floor that I want to move and on the lower level there is a toilet right below it. The pipe is cast iron and looks to be 4 inches coming up from the basement. Is there any chance this stack could be shared with the toilet or shower below? The pipe converts to 2.5 inches od just above the toilet on the top floor (as there's a stack 4 inches to the roof in another location). There is also another vent pipe coming up about 16 inches away from this stack, but it is only two inches od (could that be for the toilet and shower below?).

Main question is whether that stack could be shared because he thinks we can just cap it. I don't want to break up the nice bathroom below to find out and I don't want to cap a vent for the basement.
 
Discussion starter · #4 ·
What I'm wondering is whether or not the drain that the toilet on the upper level uses is also being used to vent the basement toilet. It is cast iron and looks to be over 4 inches.
 
#6 ·
carlspackler said:
What I'm wondering is whether or not the drain that the toilet on the upper level uses is also being used to vent the basement toilet. It is cast iron and looks to be over 4 inches.
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Yes the 4'' cast iron stack is probably the vent for the basement toilet. It wouldn't make sense to run a seperate vent for a toilet located within a few feet of the stack.
 
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#8 ·
Here, in Idaho we use the Uniform Plumbing Code, floor-to-floor venting is not allowed. And even with wet venting on the same floor, a stack must be increased by one pipe size if there is one fixture above another. So it depends on the code where you are. I've seen houses built here before the turn of the previous century that would have passed the modern code, and I think it's just good plumbing to separately vent different floors.

Old farmhouses in this area commonly had a single main 4" stack and some of the fixtures had no vents at all, predating the codes. Typically, a kitchen sink had no vent and people just put up with the smell and gurgling noises.

Then the old Idaho code came in and every fixture had to be vented. Again, typically, some drains such as kitchens and washing machine drains were undersized. Modern washers tend to overflow them, and the drains tend to be hard to clean. I like the newer codes (~30+ years old) that require 2" drains on washers and kitchens and separate vents from floor to floor. And I really admire the plumbers who, in the late 1800's, plumbed that way.
 
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