Sink drain line

homeantFebruary 10, 2006

I am about to start a major kitchen remodel. The kitchen designer has moved the sink (on paper) across the kitchen from where it currently is.

The floor will come up during the reno to run a new drain line across the kitchen to tie into the existing waste stack.

The home is a bilevel, so there is no basement, and no access from the rooms below.

So here's the question(s) -

1. The horizontal run of the sink drain line will be about 10 feet, but can only drop about 9 or 10 inches in that span because it will be in the existing floor. Is this acceptable?

2. Unfortunately the floor joists run perpindicular to the piping run I need to make. What is the accepted method of getting from the sink to the waste line? Notch beams? Drill beams and use a flexible line? No clue.

Any thoughts?


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The length of your run is 10' and you are required to have a 1/4" per foot pitch, therefore the drop is 10 x .25 = 2.5".

You may not cut notches in the center 1/3 of the overall span of a joist.

the maximum depth of a notch may not exceed 1/6 the overall depth of the joist.

You may drill holes anywhere in the length of the span, however no hole may be closer than 2" from the top or bottom edge face of the joist and the maximum diameter of the hole may not exceed 1/3 the depth of the joist.

Another problem you will need to figure out is venting. A kitchen sink requires an 1-1/2" waste line, and under the International Residential Code the maximum distance an 1-1/2" line may run from a vent is 6' from the trap weir to the vent opening. Under the Uniform Plumbing Code that distance is reduced to 3'6".

This means that you will need to plan on creating a vent at the new sink location.

    Bookmark   February 10, 2006 at 10:57AM
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Thanks lazypup.

I've been thinking this over since your reply.

The floor joisrs are 10 inch, and given the code specs you outlined, I think I can make it from the new sink location to the wet vent where the current sink drains, and still be within the guidlines.

I will create a vent at the new location by either going up through the roof, or using an AAV in the attic or under the sink.

A contractor friend also suggested cuting a section of joists out and installing headers to create a bay in which the drain line can be run. There are two walls below this area that would carry the headers. He thinks this might be better than drilling holes. Sounds like more work to me.

Another thing - if I go with drilling holes, the only way to get 10 feet of pvc through there is to do it in several pieces with couplings. UNLESS there is a flexible 1.5 inch pipe available. Is there such a thing that can be used?


    Bookmark   February 21, 2006 at 8:06AM
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There is no flexible pipe that is approved for DWV service. The major national codes require Sched.40 ABS or PVC, while some local codes will permit sched.30 PVC.

Do not confuse sched.30 PVC with SDR-30 PVC. SDR pipe is made to the SDR (size dimension ratio) standard and while it is approved for use in house sewer or storm drain lines, it may not be used inside a structure.

    Bookmark   February 22, 2006 at 9:05AM
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OK, I'll make sure it's Schedule 40 PVC.

I've seen comments in other threads regarding the AAV's (Studor). I know that a plumber would much prefer a "real" vent that "breathes" in and out. In your experience, have you seen problems with using an AAV? This

Also, which method would you find more acceptable to run the drain line:

1. Drill holes through floor joists and use short pieces of pvc with couplings tomake the run (probobly 4 or 5)

2. Create the "bay" as described in the post above, which would give a clear run, and no piecing. This method would require some major construction work (by me).

    Bookmark   February 22, 2006 at 10:20AM
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I have a situation like this. What can I use to span 10' to the outside basement wall then another 16' to the septic out?

I can use 2' from the joist to get to the wall where the 10' is started.


    Bookmark   October 31, 2006 at 11:21AM
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The International Residential Code requires all structures to have one "Main Vent". After that you may have an unlimited number of AAV's. By contrast, the Uniform Plumbing Code only permits a maximum of one AAV per structure, with the expressed approval of the Authority Having Jurisdiction in your area.

In all cases when an AAV is used it must be in and accessible location to permit periodic inspection and replacement if necessary.

In function an AAV is simply a small spring loaded rubber diaphram that will open when the pressure inside the pipe drops below standard atmospheric pressure to allow air to enter the pipe.

In reality standard atmospheric pressure is only 14.6psi and the pressure differential between atmospheric pressure and the reduced pressure in the pipe is seldom more than 2-3psi so at best it is an iffy situation. Couple that with the fact that kitchen waste will often contain hot cooking oils that will vapor off in the drain then condense on the inside of the pipe or on the diaphram leaving a sticky film that will further retard the AAV's ability to perform. For this reason most plumbers regard the use of AAV's as a last resort type option. In a situation where you cannot achieve a vertical vent through the roof a much better option is to create an "Island Loop Vent".

To create an island loop vent you install a vertical riser from the drain up to the desired waste arm location and install a Tee for the Waste arm then you extend upwards, install an 1/8bend(sanitary 45deg elbow) extend up slightly and install a 1/4 bend. You will have a line entering 1/4 bend at 45deg so the quarter bend will now make an outlet downward at 45deg on the opposite side. Extend that downward equal to the first 45 deg. then install an 1/8 bend turning down. On this riser at the elevation of the waste arm you install another sanitary Tee with a cleanout plug then continue the line down to the horizontal drain line. You now have two risers interconnected on top that form a loop with the horizontal drain below. (If you would like an illustration of the island loop vent send me an email to and i will be glad to return you one.)

While building a bay is certainly an option given that I am neither an engineer or certified framer and understanding the cost of creating one, I would consider that a last resort.

You will find that 1-1/2pvc is quite a bit more flexible than what it appears. If you start the run from the low end where the holes are closest to the bottom of the stud you should be able to push the pipe through. If not, you may use an unlimeted number of couplings and make the run with sections of pipe.


Code permits both sched.40 Pvc and ABS pipe for both the DWV run inside the structure and the sewer pipe from the structure to the septic tank or municipal sewer however code does not permit glueing dissimilar pipe (PVC to ABS). Therefore the best choice of material would be to continue with whichever product is used to make your present DWV layout. If you have cast iron DWV pipe, you may then use cast iron, PVC or ABS. the choice is yours.

    Bookmark   October 31, 2006 at 12:44PM
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Hi -
I am the original poster from way back in Feb.
The job is done and went w/o a hitch.

I ran the drain line from the existing stack on one side of the kitchen, to the other side of the kitchen 12 feet away, turned left and continued for another 6 feet.

The 12 foot run went through 7 2x10 floor joists. I drilled each joist, keeping within the code limitations of distance to top and bottom of joist. Each hole, of course was consecutively higher to maintain the proper pitch. I wound up using a coupling between each joist. As lazypup mentioned however, the pvc is more flexible than you might imagine.

I did not go with an AAV after all. I found a way up a wall, into the attic and out the roof. After talking to several plumbers, they scared me out of it.

Job is done, sink drains fine, no leaks, no gurgles.

Thanks for all who helped me out.

Donald - The folks here are amazingly helpful and professional. Be sure to state your situation and question clearly, and they are sure to help you out.


    Bookmark   October 31, 2006 at 12:59PM
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