Bathroom - Converting from double sink vanity to single

Calyptra4March 7, 2012

Hello all!

New poster here on Gardenweb but I have been a lurker for a very long time. Quick info: live in a 1918 fixer upper. Master bath was redone in the 70's, bad. We have a 66 inch double vanity that takes up a whole wall and I want to rip it out and install a single sink 48 inch vanity. I haven't open up the wall yet but I wanted to know: is there a way to cap the plumbing for one of the sinks? Is there a way to do this without calling a plumber? We are in the planning stage for our hopefully DIY remodel and so any suggestions appreciated!

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Unless you have a really weird setup the sinks join in the cabinet and then go into one drainage pipe. The same for the water lines. One set (hot and cold) come into the vanity then split for both sinks.

    Bookmark   March 7, 2012 at 8:10PM
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Count mine as really weird then! (and on only a 54" vanity!)

I definitely have 2 drain lines, and 2 sets of supply lines for my double vanity. I will be interested to hear what the OP has.

    Bookmark   March 8, 2012 at 1:12AM
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You will need to make a couple slight alterations however it is impossible to know for sure what you will have to do until the wall is opened up and we can see the present layout of the water & drain lines. The good news is that even if you have to make alterations, they are very simple and certainly well within the skill level of an experienced DIY'er.


(See attached illustration)

Assuming that the two sinks were put in to code it is not nearly as weird as Hendricus would have us believe.

Under both the UPC & IRC if the horizontal center to center distance between the two drain openings does not exceed 30" they may be combined in the same manner as connecting a kitchen double sink, then connected to a single trap & waste arm.

Under the IRC if the CTC distance exceeds 30" you may attach a double wye on the waste arm and run a separate line to each trap, with a cleanout on the end of the WYE, Providing the TDL (total developed length of either drain does not exceed the code mandated maximum trap weir to vent opening distance.

Under the UPC if the horizontal distance exceeds 30" each sink must be provided a separate fixture arm. (UPC prohibits connecting two traps to one fixture arm).

    Bookmark   March 8, 2012 at 8:42AM
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lazypup thank you for all the illustrations. We are planning to get a look behind the wall this weekend. But from what I can see so far, our sink looks like the UPC greater than 30. If this is the case, should we cap the second sink waste line? Or can we cut them both bank to the central line and rebuild one from there? I have absolutely no plumbing experience so I apologize if I need things explained to me like a 5 year old.

    Bookmark   March 8, 2012 at 11:57PM
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I would love to tell you that you can just cap those lines then install a fixture arm stub out where you need it, but I cannot give you a finite answer until we know where the vent is connected.

If I might suggest, as soon as you have the wall opened up take a picture of the layout and email it to me. I will then be able to see how the lines run and where the vent is connected, then I could give you a final answer. Also try to get the water supply lines in the photo and I can advise you how to correct those as well.

Email to

I check my email a half dozen times a day so I should be able to get a quick solution back to you and I will then post the solution so others watching this post will be able to see the results.

    Bookmark   March 9, 2012 at 4:31AM
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Silly me...I seem to have a typo on my own email address above..

    Bookmark   March 9, 2012 at 5:04AM
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Sorry for not responding anytime sooner. I got a bad case of the flu and had to hold off taking out the vanity. Unfortunately, before we could take out the vanity, a pipe burst in the bathroom and flooded it, the downstairs kitchen, and my basement. We are in the process of getting the insurance to come look at it and hopefully pay for some of the damage. We are going to have our contractor change the plumbing out so we don't have to worry about doing the conversion from double to single ourselves. I really appreciate all your input, esp. lazy pup. That diagram was awesome and really helped me to understand what was going om under our sink. Here are some pics from our flooded house:






    Bookmark   March 20, 2012 at 2:33PM
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