908.2 Wet Venting a Bathroom Group (UPC)

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Michael MacQuigg

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Hello all. I'm looking for guidance on the attached plumbing configuration for two bathrooms. I had a discussion with a local inspector (UPC, no relevant amendments) who stated that it wouldn't work but did not elaborate.

908.2.1 My dry vent connection is connected at the bathtub trap arm (dedicated 2-in dry vent at each bathtub) and meets 905.2 and 905.3.
908.2.2 The discharge into the wet vent includes the lavatory and bathtub (3 dfu)- I read this section as total dfu going into the pipe upstream of the trap that is wet-vented (the toilets)
908.2.3 Trap arm length on the toilets seem fine (<10 ft), the vent pipe is below the weir but thats ok because its a toilet.
908.2.4 The toilets (water closet fixture drains) are downstream of other wet-vented fixtures (there are none)
908.2.5 The kitchen and laundry drain into the 4-in pipe downstream. Those fixtures are conventionally vented.

wet-vent.jpg
 
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James Henry

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Thanks for the response James. I'll ask that when I talk to him again. Is that linked to particular code section or just an impression of something that might be throwing him off?


Yes, it's in the code, I don't know the section off the top of my head but it's there. I see your trying to plumb back to back bathrooms. Laying a drain on top of a drain is something to be avoided. if the lav and toilet drains were on the same plane he might have approved it.
 
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Jeff H Young

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Im not really up to date on horizontal wet venting as when I did a lot of new home work it wasent code. So it never looks right to me ha ha. But I think the problem is where those 4x2 wyes are and nothing to do with thembeing at the higher elevation. I think the 4x2s need to be between the 4 inch wye and the closet bend. The Lavs and tubs are fine but your W/c s are not vented properly I think you could say the W/C have no vent at all the vent should be taken off downstream upstream dosent count and is not a vent basicaly you just branched off the main and put a toilet in no bueno. Took me a bit of head scratching but thats how I see it .
 

Jeff H Young

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I was thinking this was a bad install but rethinking it as Im not well vered on horizontal wet vents
 

Michael MacQuigg

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Thanks for the responses. I've been asking around and others have suggested that the ~1' stretch between the two toilets breaks the wet-vent requirements because the second toilet is technically wet-vented by the first. I agree with that, at least in terms of code compliance. However, using a double wye there (instead of the two 4" wyes) would have two waste flows colliding. That seems worse that than the having the short stretch that causes the second toilet to be wet vented by the first. Maybe the inspector could appreciate that?
 

Jeff H Young

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I came into plumbing 30 some years ago we could horizontal wet vent, now that things have changed I never really learned it. So had to back off a bit on this.
 

wwhitney

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(2015) UPC 908.2 allows horizontal wet venting for a bathroom group. Per the definition in Chapter 2, a bathroom group includes at most one toilet.

So the problem is the second toilet. If you keep each bathroom group separate, wet venting each toilet, and then combine the horizontal drains further downstream, that should be compliant.

Cheers, Wayne
 
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Jeff H Young

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(2015) UPC 908.2 allows horizontal wet venting for a bathroom group. Per the definition of bathroom group in Chapter 2, a bathroom group includes at most one toilet.

So the problem is the second toilet. If you keep each bathroom group separate, wet venting each toilet, and then combine the horizontal drains further downstream, that should be compliant.

Cheers, Wayne
Thanks Wayne, I get what your saying keeping seperate bathroom groups but is it nessesary to have the wye for the tub and lav downstream of w/c ? or would this been legal if it was the same but just a single toilet? BTW the 2 inch wet vents should have long sweep 90s
 

wwhitney

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I believe the water closet has to be the last wet vented fixture. From the 2015 UPC:

908.2.4 Water Closet. The water closet fixture drain or trap arm connection to the wet vent shall be downstream of fixture drain or trap arm connections to the horizontal wet vent.

Cheers, Wayne
 

James Henry

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(2015) UPC 908.2 allows horizontal wet venting for a bathroom group. Per the definition in Chapter 2, a bathroom group includes at most one toilet.

So the problem is the second toilet. If you keep each bathroom group separate, wet venting each toilet, and then combine the horizontal drains further downstream, that should be compliant.

Cheers, Wayne


I think it's one or two bathroom groups unless it has changed. depends on the year.
 

Jeff H Young

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Ok Michael MacQuigg. I got a handle on whats wrong with it but what did you and your Inspector decide?
 

Mr tee

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I'm too old-timey and too far away from the field to be fluent on horizontal wet vents, but it looks like there are too many turns on the lav for a line without a cleanout.
 

Mr tee

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Thinking on, it might be simpler to plumb the two bathrooms separately and hook them together downstream.
 
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