We had a single sink vanity in place. Now we're remodeling and will be getting a 60" double sink vanity. Unfortunately I cannot use the stubs/drain that are existing, because the vanity has cabinet/drawer vertical supports that are right where the current supplies stub out.

Can someone tell me how to go about resolving this? I can sweat pipes and know about the fittings for the drain, and the tees, elbows, etc. My main concern is the layout & design since I'm not a plumber. Mainly the drain line - I'll have to drill large holes through several studs to pass the ABS drain through to both sinks. What is code restriction on size of holes to drill through studs? And how many holes can I drill and how far vertically between each hole? I'll have to drill holes for hot, cold, and drain of course.

First check the thickness of the wall, it has to be a 6 wall to get drain pipes through stud. If so, you drill 2 1/2" hole in center leaving 1 1/2 wood to each edge. Or you notch stud and put nail plate over notch. Drain slopes 1/4" per foot. You need 1 1/2 wood to edge for nail protection or nail plates, other than that put supply where you want.

Hmmm... just 2x4 wall (exterior). I guess when my house was built 30 years ago the code was different.

In this case what do I do?

Well you are not going to be able to go through studs. Unless you live where it never freezes you can't put supply in exterior wall. Can you go below, change drainage and come up wall where you need?

I'm in NC - freezes some, but nothing like the northeast or midwest. These supplies for the sink have been in an exterior wall for 30 years.

Also, the drain is already cut through the 2x4 stud as it is - always been that way. Not sure where to go from here.

Are you pulling a permit for this job, will you be inspected?

I have not pulled a permit and will not be inspected (there were electrical things that would have had to come up to code that would have made my cost astronomical). That being said - I don't want to cut any corners... I want to do everything up to code within good reason. I.e. if I'm not suupposed to drill through a 2x4, then I want to figure out how to do it right.

You may have to create all of your drain lines inside the vanity cabinet and then try to exit into the old lateral drain line. Sounds like this would be difficult due to drawers and cabinet walls/supports. Codes are there for a reason, usually someone tried something and it failed so the code was written to prevent pthers from the same mistake. Most of us will shy away from giving advice on skirting code. Maybe the polumbers will pick up on this and have a better slant. Harold's advice re: the studs drilling is correct.

OK, so someone cheated and went through one stud, didn't substantually weaken wall but do you want to go through two or three more. If you have galvanized drain pipe, you ain't going to drive a nail into it. Repeat, can you go under floor?

I repeat! - Definitely not trying to skirt code, and certainly don't want to make my wall weaker! This is why I came to ask you guys.

I believe I could probably go under the floor, adding some more time, but not too bad. However I haven't taken up that part of the floor, so I'm not 100%.

Next questions if I can...
1)If I do go under the floor for the drains, it's OK to drill that whopper hole through the bottom plate of the wall?
2) OK to drill through joists for drainage? If so, I'm presuming I bring them down through the plate into the joist cavity, 1/4 bend & head to where they'll intersect with the existing/main drain, and join in correct?
3) If I pull up the floor to do the drain, should I also handle the supplies in the joist cavity or take them through the studs above the floor (since the holes are smaller).

Correct. Chances are, that if you have a crawl space the horizontial drain pipe will be below the floor joist, not through them. Your choice but I would bring supply up through floor, just to be safe. If horizontial piping is below joist you should be able to tee off drain and come up through wall where you want to. Bottom plate not load bearing between studs and nailed to floor joist so cutting will not harm. Also have to figure out where vent pipe is.

Unfortunately for me this is 2nd story, with kitchen below. So I'll have to go through joists.

What's the posibility of increasing the wall thickness by adding 2x2 to edge of existing studs. Any windows in that wall. Could you give up 1 1/2" of space?

Ugh. There is a window. Also the back of the shower is on that wall, and I just set my plumbing drain in the center (which was a pain!).

I am definitely not being arguementative but if you build it to code but skip the permit you are in violation of the code. That's just how town building departments operate. We are still trying to help you with a fix but its difficult when we can't see everything so we keep asking more questions. How about removing the drywall behind the new vanity and setting the vanity another inch or so into the room, is that posible?

I understand your point about the code, but you must also understand mine - I was only adding an outlet in a circuit - the existing circuit was 15A. Code requires dedicated 20A to the sink, to be shared by nothing else. Basically if I got this inspected, I was going to have to pay an electrician & crew to rewire several circuits and run some new ones & fish wire walls... probably $1000 to $1500. All for a $5 outlet.

I will post some pictures later to get some more info.

Waiting for pics before I dive into this. :)

You can handle the window, could you build out the wall up to or beyond the end of the new vanity then have a joggle in the wall back to original thickness.

Here are two pictures...

In my area it is perfectly OK to drill 2" hole through 2x4 wall. But it has to be drilled not cut with sawzall. Moreover, you will be cutting no more than 1 - 2x4 on each side. You can use 2x 1 1/2" double (cross) SanTee and 1 1/2 pipe to each of your drain. As far as water goes, you can use double angle stops and longer supply lines. Angle stops should fit behind the drawers.

I'm not sure about keeping the stops behind the center - not sure there's room behind the drawers.

Bumpin' back up to get others opinions...

For more info & detail here's my best attempt at a dwv diagram for my situation... The blue box is the room I'm working on. Solid lines are things I can visually see - either the wall is out or the floor is up. Dotted lines are my best guesses at where things are. The red room is an adjacent bathroom.

After seeing you pic, I think I'll back away (just a little ) about the concerns about drilling the studs. It appears that you would only have to drill one more stud to do the drain. I think I would notch that one. That would leave you 1 1/2 material on the far side. Put a piece of strap iron on the front edge, you need nail plate anyway. A strap about 1' long with at least two screws top and bottom should restore structural integrity of the stud. I also notch studs for supply keeping them at the front edge and on the interior side of the insulation. Hopefully the right hand sink won't be too far away from the vent.

Thanks Harold - I'll take that approach I think. 2 questions...

1) Where does one get the strap iron things? I saw some of these type things @ Lowe's, but they were stainless steel and to me didn't look very strong.

2) How do I route the supplies around the existing drain? In other words, as you look at the picture, the supplies will have to be routed to the right, around the drain somehow. But the drain line takes up the whole wall cavity.

Strap iron is just flat metal at HD or Lowe's where they have short lengths of flat metal, angle iron and metal rods. Get the thinnest you can. Something about 1/16 would be best (I don't know what gauge that is). Any metal shop would have thinner stuff, its going to cause bow in drywall but it will be hidden by vanity. 1 to 1 1/2 wide should do.

Hard to tell from photo if you have any space between drain and exterior wall surface. If you do, cut drain right above plate, install a 22 1/2 turn, pushed against exterior wall, then short piece of pipe. Then another 22 1/2 back to drain. If you can't find 22 1/2 use 45's. Hopefully that gives you 1/2" between drain pipe and drywall. If you can't do that, just put supplies on front edge of stud, drywall above and below, cover with tape and mud. Be hidden by vanity.

PS
After thinking about it for a minute probably easiest to just put supplies on front edge of studs. Just tape and mud over to keep drafts out.