Attaching vent to back side of closet bend

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puddi

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Hello everyone

I have a configuration where the toilet drain runs in the bay between two floor joists in the “forward” direction - that is, the direction you’d be facing when sitting on the toilet - out to the main sewer. This means that a vent rising vertically from the drain within 6’ of the toilet trap (I’m in UPC territory) would poke up through the bathroom floor - not good. And, because of the prohibition on horizontal vents below FLR, the vent can't jog sideways through a floor joist to a convenient side wall. The joists are only 2x10 so the angle isn’t enough to qualify as vertical.

The wall behind the toilet is the perfect place for the vent to rise, but how to get the vent over there? The FLR/horizontal rule gets in the way just as it did for getting to a side wall.

It seems to me that this situation would be pretty common so I’d assume there’s a solution.

So I’ve got two questions. First, is there any approved way to attach the vent to the back side of a closet bend? Conceptually, like using a quarter bend, with heel for the vent (I know UPC doesn’t permit that). But how about a combo wye and 1/8 bend, with the vent coming out the back? Second, does the FLR/horizontal vent restriction still apply if the vent is washed? I could potentially drain a lav through that pipe.


Thanks!
 

Terry

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That would be like having a santee on it's back. Never a good idea.
And not to code.
A lav can wet vent a toilet when it's run with 2".
 

puddi

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Thanks for the prompt reply, Terry, Yes, I figured that likely wouldn’t be OK.

The toilet is upstairs, above an open area. The drain has to run horizontally forward from the toilet until it can turn down at an exterior wall about 11 feet from the trap. Conveniently, the floor joists run this way too. The drain can’t run in the opposite direction because there is no place for it to turn down. Going sideways from the toilet is also not good for similar reasons, plus the floor joists are a problem.

But the UPC in effect requires that the toilet drain must pass directly beneath a wall within 6 feet of the trap to attach a vertical dry vent . That’s pretty restrictive! Here, the drain won’t pass beneath any walls within 6 feet. Even the bathroom wall beneath which the drain passes is 7 feet away. Only a horizontal vent can reach the exterior wall, or the bathroom side wall.

Could one invoke the “unless prohibited by structural conditions” exemption of 905.3 here? Or am I missing something?
 

Reach4

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A lav can wet vent a toilet when it's run with 2".
Does the vent above the lav santee also need to be 2 inch in UPC?
But the UPC in effect requires that the toilet drain must pass directly beneath a wall within 6 feet of the trap to attach a vertical dry vent . That’s pretty restrictive! Here, the drain won’t pass beneath any walls within 6 feet. Even the bathroom wall beneath which the drain passes is 7 feet away. Only a horizontal vent can reach the exterior wall, or the bathroom side wall.
If you use 4-inch, that distance increases to 10 ft. You may be able to slope 4 inch at 1/8 inch per foot if the inspector is ok with that.

Could one invoke the “unless prohibited by structural conditions” exemption of 905.3 here? Or am I missing something?
I am not a plumber, but it sure seems like it ought to apply to me.

How will you vent the lavatory? Some areas in California will allow AAV, tho that may or may not require permission.

Locating a lav on the vent that you were going to use as a horizontal dry vent would seem to solve your problems.
 

wwhitney

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Does the vent above the lav santee also need to be 2 inch in UPC?
Yes, under the UPC, the entire vent path for a WC has to be 2", both the wet (if any) and dry parts.

If you use 4-inch, that distance increases to 10 ft. You may be able to slope 4 inch at 1/8 inch per foot if the inspector is ok with that.
Under the UPC, oddly not for a WC. A WC is 6' regardless of drain size. And trap arms have to be 1/4" per foot even in 4". See the footnotes here:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/10/traps-and-interceptors#1002.2

Cheers, Wayne
 
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