Adding laundry sink to laundry room with existing washer

[Chris Johnson]

Hi All,
First time poster here. I have a tight laundry room space and would like to add a utility sink. The washer and existing standpipe as well as the AAV were installed and passed inspection a couple years ago. The drain pipe in the wall drops down vertically. There IS a p-trap for the washer standpipe, you just can't see it in the photo.

I'm contemplating two options:
(A) Leave the existing washer standpipe and trap as is. Give the sink its own p-trap and connect the trap arm to the vertical drain pipe in the wall at a lower point than the washer trap arm. I'd use a San Tee on its back before the wall connection to connect the sink arm to the vent at a point above the sink.

(B) Do exactly what's shown in the IRC diagram below. As such, I would lower and extend the existing washer standpipe/p-trap down several inches and connect my new sink drain to the standpipe ABOVE the existing p-trap with a simple horizontal run. The trap arm would then just connect to the vertical drain line in the wall in the same way it currently does, just lower down.

Option B has less exposed piping but is sure to raise some eyebrows despite being IRC compliant.

Note: I'm in Los Angeles which uses the California Plumbing Code (UPC) and not IRC, however, the CPC does say:
"Each domestic clothes washer and each laundry tub shall be connected to a separate and independent trap, except that a trap serving a laundry tub shall also be permitted to receive the waste from a clothes washer set adjacent to it."

Seems nebulous and open to interpretation to me, but what do I know!


Option A:

Option B:

 

[wwhitney]

I'm surprised the AAV was inspected and approved in LA.

Go with (A). Either way you're opening the drywall, since (B) requires lowering your standpipe trap. That means (A) doesn't seem like much extra work.

Is there really just an elbow in the wall to the left in your picture? If you open things up, you could put in two stacked san-tees, the lower one for the laundry standpipe (vertical wet venting requirement), and then put your vent riser in the wall, terminating at a ventilated wall box for the AAV.

You raise an interesting point about the UPC language "that a trap serving a laundry tub shall also be permitted to receive the waste from a clothes washer set adjacent to it." It's commonly understood, I believe, to mean "receive the waste discharged through the laundry tub," but it doesn't actually say that. So you could push the interpretation to mean that the IRC diagram is allowed by that language.

Cheers, Wayne

 

[Sponsor]

 

[Chris Johnson]

Thank you Wayne, that's really helpful. It's wonderful to get such a quick response. Option A has a lot more bulky piping that's all. The ABS is all exposed so minimizing the amount of it (including any new additional venting) is still preferable for me.

And thanks for the tip on hiding the venting. I'm not sure I understand completely. Are you proposing putting two vertical vent pipes in the wall cavity?

Re: the AAV in Los Angeles, check this out:
https://ipscorp.com/pdf/studor/StudorApproval_CityofLosAngeles_Exp_01-01-18.pdf

It was actually the inspector who suggested the AAV to my contractor.

 

[wwhitney]

Thanks for the pointer on AAVs in LA. Item 13 in that document is a potential issue for you: 'Washing machine horizontal branch lines shall be a minimum of 3" in diameter.'

A couple points here per the definitions in Chapter 2 of the UPC: "horizontal branch" can include vertical segments, and it seems to exclude fixture drains, which to paraphrase are drains serving only one fixture. But as soon as you bring in another fixture, you create a horizontal branch (unless you are bringing it into a stack or the building drain).

https://up.codes/viewer/california/ca-plumbing-code-2019/chapter/2/definitions#horizontal_branch

So for you to add a second trap for the laundry tub, you'd need up size the drain to 3" starting at where the laundry tub and standpipe drains join, if you want to continue venting with an AAV. The size and configuration of the drain after it enters the wall is therefore very important.

Your single trap options are to just discharge the clothes washer into the laundry tub, or to use the IRC diagram configuration, arguing that the language in 1000.2 does not require the clothes washer to discharge into the laundry tub basin, just through its trap. I didn't see anything in a quick glance at Chapter 8 that would prohibit the IRC configuration.

Cheers, Wayne

 

[Chris Johnson]

Amazing. You're the best.

Well, can't upsize the drain in the wall and subsequent floor now! It was passed by our inspector as I mentioned, and there's no going back and breaking the wall/floor etc.

I'm inclined to do Option B, the IRC version. I'm not getting a permit for this new sink in any case and I like that you see an argument to be made about the UPC language.

 

[Chris Johnson]

Amazing. You're the best.

Well, can't upsize the drain in the wall and subsequent floor now! It was passed by our inspector as I mentioned, and there's no going back and breaking the wall/floor etc.

I'm inclined to do Option B, the IRC version. I'm not getting a permit for this new sink in any case and I like that you see an argument to be made about the UPC language.

And if I ever sell this house, I can just stick the washer hose in the sink for any inspection and call it a day
That is assuming a 24" or less horizontal run from my sink drain to its p-trap is allowable.

 

[wwhitney]

Well, can't upsize the drain in the wall and subsequent floor now! It was passed by our inspector.

Right, as long as it's just the washing machine, it can be 2". It's just that under LA's acceptance of AAVs, you can't add anything to a 2" drain for a washing machine that is vented by an AAV.

One thing the inspector missed is using the san tee on its back for the vent takeoff. Under the UPC that should be a combo. Since it looks like you're going to have to lower the trap arm anyway for your new laundry sink, when you redo it you can change that to a combo.

Cheers, Wayne

 

[Chris Johnson]

Right, as long as it's just the washing machine, it can be 2". It's just that under LA's acceptance of AAVs, you can't add anything to a 2" drain for a washing machine that is vented by an AAV.

One thing the inspector missed is using the san tee on its back for the vent takeoff. Under the UPC that should be a combo. Since it looks like you're going to have to lower the trap arm anyway for your new laundry sink, when you redo it you can change that to a combo.

Cheers, Wayne

Thank you! I like your idea of using a vertical San Tee and hiding the vent stack with a recessed valve box for the AAV. That would be a San Tee and not a combo in that case (vertical use), right?

 

[wwhitney]

For the UPC:

In drainage, you only use a san-tee when a drain is turning from horizontal to vertical, with another pipe coming out the top. [Note that vertical includes anything up to 45 degrees from plumb, and horizontal includes anything more than 45 degrees from plumb.] If the pipe coming out the top is the vent (wet or dry) for the drain coming in the side, then you must use a san-tee, not a combo. If the pipe at the top is a drain which is not a wet vent, you have the choice of a san-tee or a combo.

And for drainage in other orientations, you need to use a combo. When all three connections are vents, you can use either.

Cheers, Wayne