Too many fails here. Do you live in an area that freezes? Water line inside the wall is concerning on the exterior wall.

Otherwise, how is that drain vented and the slope looks extreme. It can be put in the wall but he may be trying to avoid the framing for some other reason. Possible he wants to have more insulation in the wall and less pipe.

Better idea is to run the vent pipe over to the drain and have the drain go down instead.

Not a fan.

Hi Vish, thanks for your advice it helps a great deal. We're out in California so no freezing. The house is a ranch with wood framing the vent is just past the right side of the window. I'll ask our contractor what's going on.

As far as codes go, the first natural place to ask would be your local inspector. I'm assuming a permit wasn't pulled on this work, otherwise the inspector would be the logical place to start. So what happens to drawer glides when you cut the cabinet? Maybe no glides in that area.

Put a stop to this madness now, otherwise you're in for nothing but headaches. These forums are full of topics where the homeowner knows it's not right, but looking for confirmation after the fact.

agreed roof35. This is under permit so I'll contact the inspector too.

No reason that should be outside the wall at all. Plus with it being outside how is it secured and held in place? You will need to cut the wall open and bore through the wood studs for it to have it fit properly though.

Did you move the sink?

That drain pipe is about 2" OD. A stud is 3 1/2" - you can't notch a stud, leaving only 1 1/2" - I think that's why the drain is on the outside of the wall. It will be hidden by the cabinet.

It depends on whether that is a load-bearing wall or not, and the size of your studs - if they happen to be 2x6 then you are in luck. If the wall is load bearing, you can only notch 25% of the width or bore 40% of the width. If it is not load bearing, you can notch 40% or bore 60%. However, if you double up the studs and bore through no more than two successively, you may bore up to 60% of the width even on a load bearing wall.

the previous comments are correct as far as boring 2 inch holes through a 2x4 stud. but you can run an 1 1/2" "dirty arm" through those studs and be fine. As long as it doesnt extend more then 3' (could be 5' I dont remember exactly) from the stack.

I was wondering would this type of design work instead if I gave this to the contractor?

If you installed it like your drawing, (and the P-trap was under the sink), I don't think there would be a proper vent for the sink drain. If water filled the existing vertical vent it would create suction and could suck the water out of the P-trap under the sink.

In the vertical section behind the P-trap you would need a vent line running straight up to above sink level , and then running across to join the vertical vent.

There is also a picture in this site of an alternative that might work. http://www.familyhandyman.com/kitchen/how-to-plumb-an-island-sink/view-all

Bruce