Converting single sink vanity to double vanity

**xceebeex** · 11-20-2011, 02:57 PM

I am refinishing our master bathroom (as part of the process of getting everything back together from the flood) and I am going to convert from a single sink vanity to a double. I don't necessarily want to take the "easy" way out just to get it plumbed, I want it to be as close to the right way to do it as I can.

The existing plumbing is kinda weird where the drain comes out of the wall off center and then goes towards the center where the single sink was. I have a feeling I am going to have to redo this anyway when I switch to a new vanity since most vanities have drawers and whatnot. I want to make sure both sinks are vented properly and have the right type of trap/drain as well so I don't run in to problems.

Attached are a couple pictures, one of what it looks like in the bathroom and the others are what it looks like from in the basement. Luckily, I have pretty easy access to everything, but unfortunately it is 2x3's which is going to make it a tight fit for the PVC. So can anyone photoshop something that is the "right" way to do it?

Thanks!

**mtcummins** · 11-21-2011, 12:23 AM

so i assume you want one bowl left of where the existing one is and one right of it? if so, you should take out that angled drain and put in a normal straight out pipe for the left bowl, then probably the best bet would be to copy what you see in the basement and bring another drain line up where you want the new right bowl. this way you reduce the holes in the 2x3 studs, and you have easy access, so might as well. above that, you'll have to take the vent off the top of the new line up and over through the studs to tie into the existing line, unless there's some better solution that i can't see higher above the picture. Often it is easier to take the vent up into the ceiling and then over to tie in to the existing line, but I can't see that.

if the water lines are in a location that won't be in the way, you can simply buy a splitter to put on the top of each supply, and run a longer set of braided stainless supply lines from each side of each splitter to each sink. If you're comfortable soldering, I'd take advantage of your easy access and put in a new set of supply lines under each sink. Also, i'd move the supply lines into the wall cavity rather than bringing them up through the floor... take them about 20" up inside the wall and turn them 90 degrees through the wall and put the shutoffs there. much cleaner install and leaves floor of your cabinets free.

**xceebeex** · 11-21-2011, 05:57 AM

Originally Posted by mtcummins

so i assume you want one bowl left of where the existing one is and one right of it? if so, you should take out that angled drain and put in a normal straight out pipe for the left bowl, then probably the best bet would be to copy what you see in the basement and bring another drain line up where you want the new right bowl. this way you reduce the holes in the 2x3 studs, and you have easy access, so might as well. above that, you'll have to take the vent off the top of the new line up and over through the studs to tie into the existing line, unless there's some better solution that i can't see higher above the picture. Often it is easier to take the vent up into the ceiling and then over to tie in to the existing line, but I can't see that.

if the water lines are in a location that won't be in the way, you can simply buy a splitter to put on the top of each supply, and run a longer set of braided stainless supply lines from each side of each splitter to each sink. If you're comfortable soldering, I'd take advantage of your easy access and put in a new set of supply lines under each sink. Also, i'd move the supply lines into the wall cavity rather than bringing them up through the floor... take them about 20" up inside the wall and turn them 90 degrees through the wall and put the shutoffs there. much cleaner install and leaves floor of your cabinets free.

Thanks for the response! Can I split off of the 1.5" pipe in the basement to run the second drain pipe up or do I have to tie in to the 4" pipe exactly like the existing one? I am thinking about re-running the supply lines in to that cavity so I don't have to drill/cut in to a brand new vanity (plus I hate having the pipes come up through the floor like that, the toilet is the same). Also, I am assuming since I will be running two separate drains then I would want a trap for each sink just like the existing one? As far as tapping in to the vent pipe, I can't really tap in any higher than what you see in the picture because right above where the drywall is cut out there is a medicine cabinet that is recessed so I can't pass behind there.

**mtcummins** · 11-21-2011, 08:41 AM

you could, but with the main line right there easily accessible, i'd just tie it in direct.

If venting is a big problem, you could put an AAV under the right lav, but this isn't preferable when you have the ability to hard vent it fairly easily.

yes, i believe it is required for double bathroom sinks to have 2 traps. in most areas, kitchen sinks don't have this requirement (my area requires it for double bowl kitchen sinks too)

**xceebeex** · 11-28-2011, 09:22 AM

Ok, well I am getting ready to go get all of the pipe and fittings I need to redo the plumbing but have another question. I am probably going to cut the supply lines in the basement and re-route them to come up through the cavity and out of the wall to the sinks, but my question is if it is worth it to go with pex? I would think it would be a little easier for me to run, but I am not sure if it is a great idea to go from copper to pex to the sink. If pex is a good way to go for this application, what is the proper way to tie in the shutoff valves and whatnot so they are “rigid”?

Also, would you do separate shutoffs for each sink or just one shutoff for the main supply?