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Is elbow in drain pipe OK?

Posted by emily_mb (My Page) on
Sun, Jul 25, 10 at 8:33

I live in a high rise with one floor above and several below. I want to move my kitchen sink 2 feet left from where it was originally. But, there is a water line (pipe?) to the left of the drainage pipe that is in the way of a straight line. So, to move the sink, the sink drain pipe would have to go around the water pipe to reach the building's drain pipe. Can I use an elbow to go around the water pipe?
The general contractor told me that after the kitchen sink trap, the rest of pipe (the extension) that runs to the drainage pipe must be straight else the water will not drain well. I want other opinions.


Follow-Up Postings:

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RE: Is elbow in drain pipe OK?

Ask this in the Plumbing forum.
It would help to know the type of filling that is in the wall and how close the the water line is.
Another limiting factor can be the height of the drain line connection above the finished floor.
However, I would cut the stack, adjust the height as necessary to accommodate the sink you are going to use, rotate the fitting as far as I could and than use 22-1/2 and or 45 degree fittings to accomplish the "dirty arm" you are attempting.


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RE: Is elbow in drain pipe OK?

I assume you're talking about the piping under the cabinet vs in the wall?
Can the water line be moved?


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RE: Is elbow in drain pipe OK?

What you are doing is foolish and illegal without a licensed plumber.


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RE: Is elbow in drain pipe OK?

Not necessarily true. Not foolish to ask questions and collect information. Not at all. This is what forums are for.

Agree that a Master Plumber will be the best resource to consult to determine finally what length the trap arm in question can be developed out to. Not illegal to lengthen a trap arm if it meets the criteria.


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RE: Is elbow in drain pipe OK?

I wasn't referring to asking but to performing an inappropriate DIY project but you knew that and for some reason wanted to twist my words.

It's a multi-family high-rise building. Any non-repair modification of the plumbing is highly likely to require a licensed plumber and a permit even if the unit is part of a condominium. I thought it would be helpful for the OP to know that in order to avoid unnecessary trouble. That's indeed what forums are for.


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Lengthening the trap arm might require enlarging the pipe or adding a vent. Would you want someone in an apartment above you modifying the drain pipes? A simple mistake could cost a small fortune in water damage and the building/unit insurance might not cover an illegal modification.


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RE: Is elbow in drain pipe OK?

good to know: there are plumbers in other forums (like terrylove.com/forums) who give lots of information. As far as I know, from having been at that forum for many years and having helped hundreds with my posts, the trap arm never takes "venting". It is the portion of the drain system between the P trap and the fixture. This might help the above post be reconsidered. It might also explain why the "foolish and illegal" statement was made. But don't just take my word for all this: go get real plumbers to comment. Licensed plumbers.


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RE: Is elbow in drain pipe OK?

'the trap arm never takes "venting". It is the portion of the drain system between the P trap and the fixture."

Actually, its the piping between the P trap and the waste/drain line fitting.


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RE: Is elbow in drain pipe OK?

yes you are right; my mistake.


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RE: Is elbow in drain pipe OK?

Nothing in plumbing codes that prevents a trap arm from being vented.

Licensed plumbers or permits may not be required for this job.

In my state, neither permits nor a licensed plumber would be required.


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RE: Is elbow in drain pipe OK?

"Nothing in plumbing codes that prevents a trap arm from being vented. "

You never vent before the trap.

Doing so would defeat the purpose of the trap unless it was a completely separate vent for all other vents.
The vents contain sewer gas, and venting the trap arm into a vent with sewer gas would remove the trap protection.

The trap is the only thing between sewer gas and the occupied space.


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RE: Is elbow in drain pipe OK?

It is true that a trap arm might have a vent after the P trap, in the wall, and before it joins the rest of the DWV drain. That might be how the venting was arranged .

Trap arms are not subject to the exact same rules that apply to the rest of the "Drain, Waste, Vent" fittings and the "Drain, Waste, Vent" pipe geometry (slopes, curves, cleanouts, connection fittings, etc). Those who learn a lot about the rules on DWV plumbing, often don't get it that trap arms are subject to a slightly different set of rules. I think the problem is due mostly to the fact that Code documents never spell out rules for trap arms in a separate section; instead they put an asterisk here and there and say in a footnote " (*except trap arms)" This makes it hard to follow. I've seen many cases where the GC or some other knowledgeable person claims that a proposed route for a trap arm is not "code", and then we all find out later that it would have been OK. The big point is that there is a difference between the rules that apply to trap arms and the rules that apply to the rest of the DWV system (the rest of the DWV system = that begins after the DWV vent, in the wall). What emily_mb has been asking about is the trap arm.

Guys, tell me if this is the best way to ask her questions:
Q1: Can I lengthen my kitchen trap arm by 24 inches? I'll keep the same 1/4" per foot slope. Right now my kitchen trap arm is __X__ inches long (distance from the wall) and it dumps into a vented stack (pipe) in the wall. It's a condo building so I'm sure that the riser pipe it connects to has venting.
Q2: I would add two bends totaling 90 degrees, or one bend of 90 degrees. Does this change anything to the previous response?

Note that this assumes the 1.5" diameter pipe will remain the same size.


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RE: Is elbow in drain pipe OK?

It seems that everyone is confused as to what a "Trap Arm"is. A trap arm is the length of pipe from the trap to the vent opening. Once the line is vented the pipe on the downstream side of the vent opening is defined as a "Vented Branch".

Code tables list all the different types of fixtures and it defines a DFU (drainage fixture unit) load value to the fixture.

By example, a kitchen sink has a rating of 3DFU's.

We then consult another table to determine the correct size of pipe. By example, under the IRC (International Residential Code) an 1-1/4" pipe may only serve 1DFU so for a kitchen sink we have to use an 1-1/2" pipe, which is rated for up to 3DFU's max.

Under the UPC (Uniform Plumbing Code) both an 1-1/4" & an 1-1/2" are rated for a max of 1DFU so we would have to use a 2" pipe.

When computing the length of a fixture arm we must begin measuring at the "Trap Weir", which is on the underside of the trap where the U section meets the trap tailpiece (the exact point were water spills out of the U section and into the drain line). We must then measure the physical length of the pipe from the trap weir to the vent opening.

Under the IRC an 1-1/2" fixture arm run with a 1/4" per foot pitch may be a maximum of 6ft total developed length.

Under the UPC a 2" fixture arm with a 1/4" per foot pitch may be up to 5ft total developed length.

you could make the offset you desire, providing you use 1/8 bends (45deg elbows to make the offset and the total developed length does not exceed the maximum.

If it exceeds the maximum, you could still make the offset but you would be required to install an auxiliary vent within the code mandated maximum length


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