Laundy/Utility Sink Wet Venting

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Dzakich

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Hello, I am redoing the laundry area in my 1967 home. Currently there is a 1.5 inch laundry stack that I will be changing to 2" to accommodate the new washer capacity. I have an original utility sink in the garage that (looks like) wet vents the washer. My plumber says that in the current configuration, even with 2" expansion, it is illegal to have utility sink wet venting like this. The only code compliant solution is to deprecate the sink and have a dedicated stack only for washer machine. I trust him, but want to understand the rationale behind the regulations and educate myself. Is this really the case and can anything be done to save the utility sink and be code compliant?

https://pasteboard.co/lrdSM1iZBgDV.jpg
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Dzakich

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wwhitney

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I'm having a hard time telling what size the pipes are in your pictures, and what the lower san-tee has coming in on the side entry.

That said, if you have access to a 2" branch drain (that is not wet venting anything downstream), and a 1.5" vent, those can jointly serve both a laundry standpipe and a laundry sink. Each one needs to have a separate dry vent takeoff (or wet vent as below), but the vents can combine at 6" or higher above both flood rims to connect to a single 1.5" vent. Each needs a 2" drain, but the drains can combine to a single 2" branch drain.

So typically your standpipe would use a 2" trap and would be vented via a 2x2x1.5 san-tee. While the laundry sink would use a 1.5" trap and be vented via a 2x1.5x1.5 san-tee. Note that under the California Plumbing Code (UPC), the landry sink drain has to be 2" after the san-tee, just like on a kitchen sink.

Oh, and vertical wet venting would be allowed with the laundry sink on top; the washer standpipe can't be on top, as it is 3 DFU, and vertical wet venting is limited to carrying discharge of 2 DFU fixtures. So then you'd have a 2x1.5x1.5 san-tee for the laundry sink above a 2" san-tee for the washer standpipe. That requires that both fixtures are within the correct distance from the stack, so the trap arm length limits are not exceeded: 60" for the 2" standpipe trap arm and 42" for the 1.5" laundry sink trap arm.

Horizontal wet venting is not allowed for either the laundry sink or the washer standpipe.

Cheers, Wayne
 

Dzakich

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I'm having a hard time telling what size the pipes are in your pictures, and what the lower san-tee has coming in on the side entry.

That said, if you have access to a 2" branch drain (that is not wet venting anything downstream), and a 1.5" vent, those can jointly serve both a laundry standpipe and a laundry sink. Each one needs to have a separate dry vent takeoff (or wet vent as below), but the vents can combine at 6" or higher above both flood rims to connect to a single 1.5" vent. Each needs a 2" drain, but the drains can combine to a single 2" branch drain.

So typically your standpipe would use a 2" trap and would be vented via a 2x2x1.5 san-tee. While the laundry sink would use a 1.5" trap and be vented via a 2x1.5x1.5 san-tee. Note that under the California Plumbing Code (UPC), the landry sink drain has to be 2" after the san-tee, just like on a kitchen sink.

Oh, and vertical wet venting would be allowed with the laundry sink on top; the washer standpipe can't be on top, as it is 3 DFU, and vertical wet venting is limited to carrying discharge of 2 DFU fixtures. So then you'd have a 2x1.5x1.5 san-tee for the laundry sink above a 2" san-tee for the washer standpipe. That requires that both fixtures are within the correct distance from the stack, so the trap arm length limits are not exceeded: 60" for the 2" standpipe trap arm and 42" for the 1.5" laundry sink trap arm.

Horizontal wet venting is not allowed for either the laundry sink or the washer standpipe.

Cheers, Wayne

Hello Wayne, and thank you for the reply. The _current_ sizes are as follows:
- Washer Standpipe is 1.5"
- Vent pipe 1.5"
- Utility sink drain 1.5"
Lower san-tee that's coming from the concrete slab is 2" x 2" x 1.5" (1.5" is side-entry arm (going to the right is the current utility sink drain from the garage)
Upper san-tee is 2" x 1.5" x 1.5"

Does this provide any more information and alters your evaluation?
 

Dzakich

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Sorry, I am still trying to read through your message and understand the best way to go about this.:)
 

wwhitney

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How far from the stack to the utility sink? How is that utility sink being vented? The horizontal drain coming in is way too low to be involved in venting that trap, every trap arm needs to be vented before the drain falls more than one pipe diameter (and for a 1-1/2" trap, within 42" of the trap).

My previous answer was based on a laundry sink near the stack, which I took to be instead of the garage utility sink, I guess based on the title of the thread. Are you just looking to upsize the standpipe to 2" and leave the utility sink alone, no laundry sink? Or is there going to be a laundry sink near the standpipe, plus the garage utility sink?

You can see the list of sink types recognized by the UPC by scrolling down to "Sinks" in this table:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#702.1

I'm not sure what category your "utility sink" would fall under, but take a note of footnote 2 and that it applies to most sink types with a 1-1/2" trap. The only sink types with a 1-1/2" trap that are allowed to have a 1-1/2" drain are private bar sinks and exam rooms sinks. Since I'm pretty sure a utility sink is not one of those, your utility sink is supposed to have a 2" drain (after the trap arm, e.g. starting at the san-tee). [And BTW, bathroom lavatories are under Lavatory, not Sink.]

Cheers, Wayne
 

Dzakich

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How far from the stack to the utility sink? How is that utility sink being vented? The horizontal drain coming in is way too low to be involved in venting that trap, every trap arm needs to be vented before the drain falls more than one pipe diameter (and for a 1-1/2" trap, within 42" of the trap).

My previous answer was based on a laundry sink near the stack, which I took to be instead of the garage utility sink, I guess based on the title of the thread. Are you just looking to upsize the standpipe to 2" and leave the utility sink alone, no laundry sink? Or is there going to be a laundry sink near the standpipe, plus the garage utility sink?

You can see the list of sink types recognized by the UPC by scrolling down to "Sinks" in this table:

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/7/sanitary-drainage#702.1

I'm not sure what category your "utility sink" would fall under, but take a note of footnote 2 and that it applies to most sink types with a 1-1/2" trap. The only sink types with a 1-1/2" trap that are allowed to have a 1-1/2" drain are private bar sinks and exam rooms sinks. Since I'm pretty sure a utility sink is not one of those, your utility sink is supposed to have a 2" drain (after the trap arm, e.g. starting at the san-tee). [And BTW, bathroom lavatories are under Lavatory, not Sink.]

Cheers, Wayne
Hello Wayne. I am attaching the image of the current setup to include the utility sink in the garage. Sorry the confusion in the title.
The utility sink p-trap entry ~ 52 in. away from the lower san-tee.
Utility sink and washer machine standpipe share 1.5in atmospheric vent pipe. See the image that depicts why the sink drain is so close to floor level.

"Are you just looking to upsize the standpipe to 2" and leave the utility sink alone, no laundry sink?" - Correct. I would like to preserve the current configuration but make sure it is done properly. No laundry sink.
 

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Dzakich

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I've read throughout that wet venting is not allowed under any circumstances for a laundry group (only for bathroom groups). Washer must have a dedicated venting and it is illegal to have 2" laundry wet vent the utility sink.
 

wwhitney

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Vertical wet venting is allowed for laundry fixtures, with limits. I'm going to call your sink a laundry sink, just to pick a name.

Your current configuration has (2) UPC violations: the laundry sink 1-1/2" trap arm is limited to 42" in length, and the laundry sink can't be wet vented by the laundry standpipe (3 DFUs). The reverse is allowed, the laundry standpipe can be wet vented by the laundry sink (2 DFUs), if the san-tees were in the opposite order vertically.

Your simplest path forward is to make the red changes below. The 42" refers to the distance where the wye branch (the vent) comes off the laundry sink fixture drain. It's also important that the total fall from the trap outlet to the wye fitting is no more than 1-1/2" (but of course at least 1/4" per foot).

You're supposed to also make the green changes, but I don't really see how it matters, and it would be quite hard to do, so it's plausible to me to leave that part out.

Cheers, Wayne


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Dzakich

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Vertical wet venting is allowed for laundry fixtures, with limits. I'm going to call your sink a laundry sink, just to pick a name.

Your current configuration has (2) UPC violations: the laundry sink 1-1/2" trap arm is limited to 42" in length, and the laundry sink can't be wet vented by the laundry standpipe (3 DFUs). The reverse is allowed, the laundry standpipe can be wet vented by the laundry sink (2 DFUs), if the san-tees were in the opposite order vertically.

Your simplest path forward is to make the red changes below. The 42" refers to the distance where the wye branch (the vent) comes off the laundry sink fixture drain. It's also important that the total fall from the trap outlet to the wye fitting is no more than 1-1/2" (but of course at least 1/4" per foot).

You're supposed to also make the green changes, but I don't really see how it matters, and it would be quite hard to do, so it's plausible to me to leave that part out.

Cheers, Wayne


View attachment 77482

Thanks for fantastic details. Your description makes sense to me. Based off your description about reversing the wet venting order and max runs for given drain diameters, does Option B (attached) satisfy the code requirements?

- Utility sink drain is enlarged to 2" to allow for a max run of up to 5 ft.
- The max drop is 1x diameter (2in) over run span @ min delta of 0.25 in/ft

The possible issue is the height of the sink trap above the garage floor. From what I read, the standpipe trap should be at least 6 in off the floor which means by the time I get to the wall between the laundry and garage, the drain/trap outlet would be at least at 2.5-3feet off the garage floor. Is there a height limit for p-trap location?

I appreatiate your time answering my questions and sharing the knowledge. I find the physics of plumbing rather fascinating. Thanks for the education.
 

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wwhitney

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Yes, option B is fine code-wise. But 30" to 36" above the garage floor for the sink trap sounds like a deal breaker. And yes, the UPC specifies a minimum 6" height above the floor for the standpipe trap.

Cheers, Wayne
 

Dzakich

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Yes, option B is fine code-wise. But 30" to 36" above the garage floor for the sink trap sounds like a deal breaker. And yes, the UPC specifies a minimum 6" height above the floor for the standpipe trap.

Cheers, Wayne
Thanks Wayne. I'll talk to my plumber to discuss out path forward. I'll update once we wrap up the plumbing.
Stay safe.
Stas
 

Dzakich

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Yes, option B is fine code-wise. But 30" to 36" above the garage floor for the sink trap sounds like a deal breaker. And yes, the UPC specifies a minimum 6" height above the floor for the standpipe trap.

Cheers, Wayne

Hello Wayne,
I am now thinking about deprecating the utility sink and its drain to just have washing machine stack and vent pipe - that's all. What is the best way to go about removing the bottom san tee from the drain that's in the concrete slab? Can I cut the sink drain and cap it (as shown on the image with blue dashed line)?
Thank you
 

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Reach4

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You can feed a laundry sink into 1-1/2 inch, and drain the washing machine into the laundry sink.
 

Dzakich

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You can feed a laundry sink into 1-1/2 inch, and drain the washing machine into the laundry sink.
Hello Reach. This is actually not a laundry sink but a utility sink in the garage. It is out of physical reach as indicated on my picture from before
 

Reach4

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Hello Reach. This is actually not a laundry sink but a utility sink in the garage. It is out of physical reach as indicated on my picture from before
I think you would be allowed to route the WM drain line, through the wall, into the garage sink. But if you consider that, get a confirming opinion.
 

wwhitney

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Can I cut the sink drain and cap it (as shown on the image with blue dashed line)?
As far as I know you can just cut it and cap it. I would suggest a solvent weld cap, and I would suggest leaving enough pipe between the san-tee and the cap so that in the future you could cut the cap off the pipe and have enough clean pipe left to easily solvent weld on a new fitting. E.g. cut it a minimum of 2" from the san-tee hub, maybe 3" or 4" is better.

Cheers, Wayne
 

Dzakich

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As far as I know you can just cut it and cap it. I would suggest a solvent weld cap, and I would suggest leaving enough pipe between the san-tee and the cap so that in the future you could cut the cap off the pipe and have enough clean pipe left to easily solvent weld on a new fitting. E.g. cut it a minimum of 2" from the san-tee hub, maybe 3" or 4" is better.

Cheers, Wayne

Thanks as always, Wayne.
 
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