Double sink on single drain dilemma

[AZHobie]

Good evening,

Looking for friendly advise on this problem. I took the mirror down and updated what I found.

The picture is what I have now as was originally built in 1988. The left sink horizontal drain is 2", the right sink is reduced to 1 1/2". The vent is 1/2" above the cross and 2" below that. There is a vertical clean out just below the cross connection going to the exterior of the house. The vent continues up to 48" above the floor then left turn horizontal for 36" then turns up between two high long (wide) windows through the roof. The orange tape represents where the vent is and where I would like the the new sinks, X marks the two spots.

The problem..I am adding new cabinetry and the new sinks need to be moved. The left one will move left another 30" bringing its new location 72" from the vertical stack. But the right sink will have the center of 33" cabinet almost exactly where the vertical drain/vent is currently located. Any Idea how I can fit the right sink drain so that it is near center of the cabinet. Glendale is IPC code.

Thanks for all the help from everybody. I assumed the vent deviated toward the right wall on the first post.

 

[wwhitney]

Several comments:

Do you know if your plumbing code is the IPC or the UPC? It may vary across Arizona, I understand.

The pipes you've called 3" are 2" pipes (2-3/8" OD), and the pipes you've called 2" are 1-1/2" pipes (1.9" OD or so).

Where a drain trap arm emerges from the wall into the cabinet doesn't have to be centered on the sink. In many ways, it's better if it's 1" off. And if it needs to be 12" off, that's OK.

What is limited is the distance from the trap under sink to the vent takeoff, along the path of the drain (i.e., the length of the trap arm). Your current vent takeoff is that 2" double fixture fitting (the cross). The UPC limits a 1-1/2" trap arm to 42", and a 2" trap arm to 60". The IPC allows 72" and 96", respectively, but those limits are only achievable if your trap arm has exactly 1/4" per foot slope, no more, no less.

The left hand trap arm was made to be 2" because it is so much longer, it presumably would have exceeded the maximum trap arm length of a 1-1/2" trap arm. It should have had a 2" trap under the sink, which is unusual but doable.

So if the left hand trap arm is presently between 42" and 60", that's evidence the previous plumber thought that that you're under the UPC. [You need to allow 6" to 12" within the cabinet to reach the trap when measuring the trap arm length.] If the trap arm is between 72" and 96", that's evidence that the previous plumber thought you're under the IPC.

In any event, moving the left sink another 30" left is a problem, as you are likely to exceed the maximum trap arm length. The simplest solution is to take the mirror down and run a new vent for the left hand sink that reconnects to the existing vent at least 6" above the sink flood rim. [So if the mirror is at least 9" above the sink, you could probably do that without removing the mirror.]

Cheers, Wayne

 

[Sponsor]

 

[AZHobie]

Thanks Wayne,

I'll check the measurements, Glendale looks to be IPC. The mirror is coming down anyway. I think I can shorten the right a few inches and it will clear the cabinet and be within 12" of the P-trap. I believe I understand what you are saying about adding a high vent line above the flood line of the sinks.

Thanks for your detailed explanation, big help!

John

 

[wwhitney]

P.S. It would be helpful to know the left-right offsets between the current vertical drain/vent center line and the center lines of the new left and right sinks. Depending on those numbers, and which code you are under, if the lefthand trap arm is just a little too long, one option you have is this:

Cut off the drain 1" above the plate and cut off the vent 1" below the mirror. Each of those gets a wye with the side branch pointing to the left. The current vertical path gets a san-tee pointing out of the wall for the right hand sink. The branch of the drain wye rises at the 45 angle until a few inches below the vertical midpoint of your cuts, and then gets a street 45, san-tee pointing left, and street 45 for the vent to reconnect to the vent wye. I would think you could reduce your trap arm about a foot this way. Actually making it up would require several shielded rubber couplings.

Cheers, Wayne

 

[AZHobie]

Thanks,

The new left sink center is 72" and right sink center is 2" right of the vertical vent. Not sure how to work around the 2x4 on the right side.

John

 

[Reach4]

Any Idea how I can fit the right sink drain so that it is centered in the cabinet. Does it have to be centered in the cabinet.

First, you tend to not want exactly centered for a p-trap, but maybe 2 inches off of center ideally. That gives you more flexiblity. You also have the option to come out at an angle.

 

[wwhitney]

To minimize further boring of the studs, consider the option diagrammed below. I would put stud shoes on all the holes. The green is 1-1/2", and the red is 2". The lefthand trap arm vent take off is an upright combo, and it can go in whatever stud bay is required to keep the trap arm length/drop under the maximums. [Bearing in mind that 6" - 12" of the trap arm is inside the cabinet itself.]

Cheers, Wayne

 

[AZHobie]

Thanks Wayne, I think I can do this, especially since I now know the vent line goes horizontal to the left at 48" high. You have been a big help.