Plumbing Double Sinks

[jyl]

A newbie plumbing question.

Designing a double vanity. Want to sacrifice as little volume to the plumbing as possible. Can you connect both sinks with horizontal pipes into a wye then to a single, shared P-trap?

[A930Rocket]

I’m going to say no, as I’ve never seen that set up before. Each sink has their own p trap and it’s tied into a single waste line in the wall.

[VINMAN]

Originally Posted by jyl

A newbie plumbing question.

Designing a double vanity. Want to sacrifice as little volume to the plumbing as possible. Can you connect both sinks with horizontal pipes into a wye then to a single, shared P-trap?

Yes you can. ( not necessarily with a wie, but a sanitary tee...)Normal configuration by code. Thats how i always do it.

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[908/930]

You can but, more chance of odor from the drain and the horizontal pipe with the P trap being far away.

[look 171]

I think its actual legal here too but we never do that. We always have separate p-traps for each sink and make connection with a long radius Tee way down below or behind the wall into the waste pipe

[look 171]

The other reason is noise. You will hear water draining from the other sink. No good

[VINMAN]

Double p- traps are against code here in NJ

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[70SATMan]

Originally Posted by VINMAN

Double p- traps are against code here in NJ

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Don’t think he’s referring to double trap on a single fixture (against code here as well AFAIK).

I just went through this design work myself. The sinks can be installed with a single p-trap as long as they are within 30” of each other. When I laid it out, I preferred separate p-traps into the wall, down through the floor into the crawl space where I teed them together.

In the event of having to work on leaks in the vanity, I liked the idea of not affecting both sinks at the same time. Also, the plumbing took up more space with a T layout before the trap YMMV.

[look 171]

Originally Posted by 70SATMan

separate p-traps into the wall, down through the floor into the crawl space where I teed them together.

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This, like I mentioned earlier, better work too. Unless its a slab, then connection should be behind the wall.

John, you have come this far, it isn't worth the small amount of trouble of opening up drywall and patching. GEt it done correctly.

[jyl]

I was not thinking of avoiding in-wall work. I am more thinking about maximizing the usable volume inside the vanity for drawers etc. Like, maybe I could have a single P trap in the center of the vanity, between the sinks, and thus have a full stack of drawers beneath each sink.

We’ve decided to replace our always-irritating single pedestal sink with a double vanity. There is 66” of width available. We looked at various double vanities, the <$1,000 ones were press-board and the actually-wood ones were $3,000++. So I’m thinking of two more options: i) find a super cool old dresser, something with a bombe front or etc, and convert it, or ii) have a double vanity custom-made to measure. Either way, if we’re going to spend money on this, I want maximum storage. The bathroom is small :-(

[look 171]

If you are doing all that, I have a solution for you but it will require some mods to the dresser drawers. I am just about to go to work now, but will get back to you later this evening.

[rockfan4]

One P-trap one sink.

I'm assuming what you're hoping for is "her sink" and "your sink".
You're not going to get that.

What I currently have is "her sink", surrounded by so many bottles of potions and elixirs that there's no way I could use it without knocking half the stuff onto the floor.
The other sink contains a makeup bag, an open giant container of Q-Tips, and both a curling wand and a hair straightener, rendering it completely unusable.

Just add more drawers. Don't expect access to any of them.

Wash your hands in the kitchen sink, or use the hose outside.

[dad911]

I did that (drawers under sinks) Each sink got a std trap, and I made rough was centered on each sink. Kept traps high with vessel sinks, and they just needed a narrow notch in each upper drawer.

[jyl]

Actually, one sink will be “hers” (wife) and the other will also be “hers” (daughter). I’ve already been pushed out to the half-bath on the ground floor, and am periodically chastised for having my stuff in view of the guests who might be offended by the sight of it.

Oregon Plumbing Code permits two sinks on one trap, with conditions

"One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry tubs of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed."

[unclebilly]

I’m pretty sure we’ve discussed this before.

In our kitchen, I installed 2 p traps for the double sink. Code allows for 1 or 2. Our dishwasher discharge ties in between them and the dishwasher hose acts as a p trap in itself.

We don’t hear any burbling when we drain one sink, neither has ever plugged, it works great.

I’m surprised any jurisdictions would not allow for one trap per sink… I suspect that like many Canadian codes, the wording allows for one trap for both sides and people read it as must be only one trap for both sides of the double sink.

[unclebilly]

As I suspected from the NJ plumbing code of 2021…

One trap for a multi compartment sink is allowed… (exception 3) but it is a ‘May’ not a ‘shall’. This means you can do one trap per sink compartment or one trap for both.

What is NOT allowed is putting 2 traps in series (one after another) without a vent between them (5.1c).



Read the code in your jurisdiction, be mindful of the ‘shalls’, ‘Mays’, and ‘musts’…

[unclebilly]

Originally Posted by VINMAN

Double p- traps are against code here in NJ

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See my post above…

[VINMAN]

Completely aware of "may"and "shall". Been a contractor for over 30 years.
I speak on experience with dealing with numerous jurisdictions and their requirements. I've done tens of kitchens, baths. Residential and commercial.
Just saying what I run into.

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[unclebilly]

That screen capture is the NJ code. Double p-traps are NOT against code in NJ (unless you meant connecting 2 traps in series).

[VINMAN]

That is what I'm talking about. Because one will draw the water out of the other.

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