Yet another code question about moving a kitchen sink

Angie_DIYJune 30, 2011


Allow me to introduce myself. I generally post on the Kitchen Forum, but need some help in moving my kitchen sink during a total renovation.

Here are two pictures of my current plumbing setup:

and a closeup:

(The second trap is for a dishwasher discharge. I may or may not include a second trap in the new setup.)

I would like to move the sink one or two stud bays (16 or 32") to the right. However, there is an obstruction in the basement under those bays, so I cannot just drop straight down and angle the lines over in the basement. I am trying to figure out if it is up to code to make the lateral connection in the stud bays on the kitchen level, then use the existing downpipes to the basement. In this picture, blue is the vent stack, and red is the waste pipe for the sink. (They wye together near the basement floor.)

Would such an arrangement meet code?

Thanks so much!


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The bad news is that your proposed plan will not meet code because you have a horizontal vent line below the flood level rim of the fixture being served. (The blue line).

The GOOD NEWS is that there is a much simpler way to move your drain and connect the vent.

First off, that blue line is redundant and totally un-necessary.

In plumbing, any line which rises at an angle of 45deg or more is said to be a "vertical line".

I have reworked your photo to illustrate the proper way to move your drain.

Note that I show the 45deg vent running through the second stud and continuing on to the horizontal drain. If you do not care to cut that second stud you could run the vent 45deg down to the point where I show the dotted yellow line, then drop the vent straight down to your drain line.

Personal note: Although it is not required by code, if it were my house I would use a sanitary tee to connect the horizont drain to the drain riser on the left side. Then install a "street 1/4 bend turning out and put a thread adapter with a cleanout plug on the top of that vetical drain line.

    Bookmark   June 30, 2011 at 2:14PM
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Dear Lazypup,

Thank you so much for your time and effort on this forum. You are very kind! (You must get sick of explaining the 45 deg rule, which I have read on many of the previous posts I found by searching!) Clearly, you are NOT a lazypup.

Would the situation change if I told you that the blue horizontal vent line is actually ABOVE the flood rim? (I know it may not look like it; that window is rather high on the wall, which provides kind of an optical illusion.) The centerline of the present horizontal vent line will be about 1" above the countertop itself.

If I have understood what you said, AND if I am correct about the flood rim issue, then wouldn't this do it? (The circle is supposed to be a cleanout plug above the sanitary tee you suggested.)

Thanks again!

    Bookmark   June 30, 2011 at 3:29PM
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You must be a minimum of 6" above the flood level rim before you can have a horizontal vent.

You could arrange the line as you have it but instead of that short horizontal vent at the top of the riser from the trap, just make a short 45Deg line from your riser to the existing vent.

    Bookmark   June 30, 2011 at 3:38PM
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Got it, Lazypup. (Just like you showed initially with your yellow dotted line, huh? ;^)

Is there any limit to the length of a horizontal drain line? (I know about the limits on horizontal *vents*.)

Again, thank you! A_D

    Bookmark   June 30, 2011 at 4:21PM
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The section of horizontal drain line from the trap to a vent is defined as the "fixture arm" and the maximum length is defined by the diameter of the line, but once the line is vented, all pipe downstream of the vent is defined as a vented drain and there are no lenght limits, providing of course that you can maintain the pitch.

    Bookmark   June 30, 2011 at 7:57PM
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Oh, dear. I hope I hadn't given incomplete information.

I just realized that one of the two vertical pipes (the galvanized in the picture) also serves as a vent for a lavatory in the basement. Unless I have my terms confused, the arrangement you described for me would then become a "vertical wet vent." (Am I right so far?)

I have a copy of my state/municipality's code. As best as I can tell, vertical wet vents are allowed for two fixtures that are on the same floor. It makes no mention that I can see of fixtures on different floors, which I take to mean that that arrangement is not allowed.

Can anyone please help me determine if my understanding is correct, or, perhaps I should say, indicate what the best way to handle this venting is?

    Bookmark   July 5, 2011 at 2:34PM
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You are correct in your understanding of code however there is still and easy fix from right here.

Cut the existing pipes in the three places as shown and remove all that cut away copper and galvanized.

Begin at the galvanized vent on the right side of the window and drop an 1-1/2". At the point where the existing horizontal galvanized ties in install a sani-tee (upside down so the slight radius curves up instead of down)

Run an 1-1/2" PVC horizontal and drop it down to connect to the galvanized vent for the basement. This line is well above the flood level rim of the basement fixture so it may go horizontal at this point.

From the bottom of the tee drop the 1-1/2" down till you can make the 45deg horizontal offset as shown.

Now connect you new sink drain to the copper drain line as shown by the white line.

    Bookmark   July 5, 2011 at 5:23PM
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Bless you, lazypup. Your kindness continues to amaze me.

Since this is a venting application, it would be okay to use a regular tee (not an upside-down sanitary tee) at the upper right, correct? The reason I ask is that I may try to use galvanized instead of a Fernco coupling. If I can use a standard tee, I can use the same pipes and stud notches. (Obviously, I can do it as you suggest if I decide to just go fernco/PVC.)

I had been pondering the layout after I posted. Based on your previous information, this is what I had come up with (before your latest post):

I think this is okay, based on what you were kind enough to post earlier. In either your setup or this one, I have to rejigger the two vertical pipes so that they don't have to cross in the stud bay. In the basement, they are in a line (as viewed in the same direction as the picture), and then one goes left and the other right. Therefore, it should be pretty easy to make the one that goes left now go to right, and vice versa. (Just thinking out loud, here, I suppose!)

Thanks again!!! Your guidance has made me comfortable that I can do this, whereas before I was uncertain. Thank you.

    Bookmark   July 5, 2011 at 7:02PM
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Well, it only took two days longer than it would have taken a plumber, and only cost me as much in materials as he or she would have charged for the whole job! ;-) But I got it moved okay.

I didn't mention I was doing it in copper, did I? :)

(Don't worry; all fittings in the drain line are DWV.)

Lazypup, thanks again for the patient help you gave me. I could not have done it without your guidance. I appreciate that.

    Bookmark   July 8, 2011 at 7:03PM
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Hi Angie,

I have really appreciated following along with your plumbing problem. I would like to confirm i understand your solution.

1. Your horizontal vent is now no longer venting the galvanized pipe that serves as a vent for a fixture in the basement. But rather
2. it is venting what used to be the waste pipe for your upstairs sink.
3. Your waste from the sink is going to what was the downstairs fixture vent pipe.

Therefore, my two questions are

Is the arrangement having waste going down what was previously exclusively the vent for downstairs fixture, and has it now become a "vertical wet vent" that you asked about earlier. And

What venting is the horizontal vent doing, and for what basement fixtures now?

Again, Great problem!

    Bookmark   January 4, 2012 at 1:56AM
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Hi, Pauled99,

I am not sure I understood your question exactly. It may be easiest for me to try to explain it in my terms.

Both vertical pipes from the basement serve the same purpose they did originally. I just crossed them left-to-right before they came up from the basement.

The leftmost copper pipe, which extends vertically from the basement and makes a right-angle turn to become horizontal and enters the galvanized tee in its middle port, only vents a sink in a bathroom in the basement. Obviously, the horizontal section is well above the flood rim of the basement fixture.

The right copper pipe comes up from the basement, turns 90 deg to the right to become a horizontal drain (sloped at 1/4" per foot), turns vertical, and is teed into the stub-out for the kitchen sink with a sanitary tee. Above this tee, it is now considered a vent. It then turns 45 deg (remaining a "vertical" vent), and then turns 45 deg the other way to go into the bottom port of the galvanized tee.

The vertical galvanized pipe vents both the basement and kitchen fixtures.

In the basement, the two downpipes are joined by a sanitary wye below the point where the bathroom fixture joins the left-hand downpipe. The single drain then goes below the basement floor to join the main (?) house sewer line.

After that picture was taken, I put steel plates over the stud notches to protect the pipes from screws/nails.

The plumbing inspector took a look at the work, *briefly* thought about squawking about the galvanized tee before realizing it was strictly a vent at that point, and then admired the job and gave it a thumbs-up.

If this explanation is not clear, feel free to ask a follow-up question.

What I learned during this process is that the plumbing codes actually make sense, even if not at first to the uninitiated. For example, as a novice, I would have turned the drain for the sink vertically instead of horizontally, and teed it into the horizontal drain line. However, that would have made the section to the right of that tee into an illegal horizontal vent. Stuff that goes down the sink could splash to the right (i.e., upstream). Since there is no water flow there to wash it down, it could get lodged there and obstruct the vent. This was not obvious to the tyro, but makes sense to me now.

Again, a thousand thanks to lazypup.

    Bookmark   January 4, 2012 at 11:52AM
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