Interesting plumbing system: offset partial wet-vent with branches after reduction. No violation of codes?

[Jan S]

Interesting plumbing system: offset partial wet-vent with branches after reduction. No violation of codes?

The system is typical. Coming up through a concrete crawlspace floor is 4” PVC with a 90-degree elbow below the floor that leads to an on-site septic. The first connection in the stack is a 4” Wye connection for a 4” toilet drain. Then a 2” shower connection. On top of that is a 4” Wye threaded clean-out. Then the 4” diameter stack is reduced to 2” diameter. The reduction fitting has a 2” 45-degree elbow on top.

The 2” PVC is pitched and runs for 4-feet before turning vertical and going up. Beyond the Sanitary Tee connection of for the vent, are two connections for a lavatory sink and a kitchen sink.

All four branches (toilet, shower, lavatory sink, and kitchen sink) use the same 2” vent. For 4-feet (from the reduction off the top of the 4” stack to the Sanitary Tee for the vertical vent) the vent is a wet-vent because the two sinks supply waste water from beyond the connection for the vertical vent.

Appears to be no violation of codes. Can anyone find anything wrong?

 

[Reach4]

Consider painting us a simplified picture with a drawing program. 900x900 pixels max.

"90-degree elbow below the floor" needs to be a long sweep or a pair of 45s.

 

[Sponsor]

 

[Jan S]

Consider painting us a picture with a drawing program. 900x900 pixels max.

"90-degree elbow below the floor" needs to be a long sweep or a pair of 45s.

Yes - the 90-degree elbow is the lowest fitting and it is a long sweep. Thanks for asking

 

[Jan S]

Here is an earlier drawing. Since the time this was drawn, the Lavatory connection has been moved to the opposite side of the vertical vent.

 

[wwhitney]

Wisconsin has its own plumbing code, so you'd need to check its provisions.

What you have posted doesn't qualify as a traditional wet vent, because (a) typically the kitchen sink would not be part of a bathroom horizontal wet vent and (b) almost all venting systems require the vent takeoff for a trap to be at the elevation of the trap, not at the elevation of your horizontal 4" drain.

But you might check the combination waste and vent rules in the WI plumbing code. That's one of the few systems that overcomes (b), the vertical leg to each sink is considered a vent. Not sure in what situations the WI plumbing code allows combination waste and vent and whether the vertical legs are sized properly for that.

Cheers, Wayne

 

[Jan S]

Thanks Wayne.

I utilized the chapter found here:
https://docs.legis.wisconsin.gov/co...and_buildings_and_environment/380_387/382.pdf

That has this chart:

It looks like the 2" diameter of fixture drain, pitched at 1/4 per foot, can have an 8-foot length to the 2" diameter trap of the kitchen sink.

Another interesting concept that I can't find in codes is: wouldn't extending a clean-out arm past the Tee fitting for a drain, provide additional air so that a trap won't be siphoned? Imagine a clean-out arm six feet long past a Tee fitting where a drain meets a wet-vent. There would be so much air space that it would be unlikely that enough vacuum would develop to siphon the water out of the trap.

 

[Jeff H Young]

I dont get into WI code but I dont think any code allows this type venting I concider the kitchen and Lav unvented sort of s trapped situation . Maybe it does count as Combination waste and vent but it rquires aproval by the AHJ befor proceeding with the build in my jusisdiction (UPC code) guys think you can just follow the guidlines but that isnt my code it requires prior aprooval And If inspector comes out and sees a crappy build that he never would have aprooved he might be tickedoff that you didnt run it by him ahead of time.
I wouldnt be suprised though for an inspector to sighn the card thgough half of them dont know a thing about plumbing so its a crap shoot

 

[wwhitney]

It looks like the 2" diameter of fixture drain, pitched at 1/4 per foot, can have an 8-foot length to the 2" diameter trap of the kitchen sink.

Yes, that's right if you have a pitch of exactly 1/4" per foot. That's based on a maximum height difference of one pipe diameter between the trap outlet and the vent takeoff, to avoid siphoning.

But you have a vertical segment between the vented 4" drain and the trap arm. So you have way more than one pipe diameter of height difference, and you have a shape that would definitely support siphoning.

So the only venting system that could allow such a geometry is combination waste and vent, which uses an oversized drain that is supposed to never be able to fill up to allow siphoning. What does the WI code say about about combination waste and vent?

Cheers, Wayne

 

[Jan S]

Yes, that's right if you have a pitch of exactly 1/4" per foot. That's based on a maximum height difference of one pipe diameter between the trap outlet and the vent takeoff, to avoid siphoning.

But you have a vertical segment between the vented 4" drain and the trap arm. So you have way more than one pipe diameter of height difference, and you have a shape that would definitely support siphoning.

So the only venting system that could allow such a geometry is combination waste and vent, which uses an oversized drain that is supposed to never be able to fill up to allow siphoning. What does the WI code say about about combination waste and vent?

Cheers, Wayne

Thanks for your comments. I will do more research.

 

[Jan S]

I dont get into WI code but I dont think any code allows this type venting I concider the kitchen and Lav unvented sort of s trapped situation . Maybe it does count as Combination waste and vent but it rquires aproval by the AHJ befor proceeding with the build in my jusisdiction (UPC code) guys think you can just follow the guidlines but that isnt my code it requires prior aprooval And If inspector comes out and sees a crappy build that he never would have aprooved he might be tickedoff that you didnt run it by him ahead of time.
I wouldnt be suprised though for an inspector to sighn the card thgough half of them dont know a thing about plumbing so its a crap shoot

Thanks for your comment. I will look into combination waste and vent systems.