Kitchen Sink rough-in placement in front of exterior wall

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Esobocinski

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Greetings all, and thanks for keeping this one of the best DIY resources anywhere.

Background: We're doing a complete kitchen rebuild. I have a general contractor but I'm doing the utilities. The kitchen sink will be along a new exterior wall with 2x6 framing, and will be a deep unbalanced double sink with one disposal. The drain will be PVC, the supplies will be copper.

I hate plumbing coming up through cabinet floors, but I live in Michigan where freezing is a concern. I don't see any Michigan code rules forbidding supply plumbing in an exterior wall, and the wall will be well-insulated, but other discussions that I read here have lead me to believe that I should not do it unless absolutely necessary, and that I should just swallow hard and go through the floor anyway.

I'll be stuck with an AAV and so don't need to worry about vent pipe: A large window above the sink prevents me from getting a vent in the wall vertically 6" above the flood rim while also getting 1/4" slope for 6 ft horizontally. I'm structurally blocked from running the drain horizontally in the wall to a new drain stack beside the window. The inspector shot down my suggestion for a modified island vent. (He won't say why -- he hates DIY'ers and tells us as little as he possibly can). The inspector likes AAVs. I hate them but I don't see a way to do avoid it.

So, the questions:

Am I correct figuring that I'd best go through the floor? Or, is that paranoid with modern insulation and I could go up the wall? I assume that it has to be all one or the other in order to allow the cabinet to be slid over them, right?

Assuming floor installation, what is the minimum distance that I should put between the exterior studs (or finished wall) and the backs of the pipes? In other words, what's the minimum distance that lets the cabinet back slip behind the pipes and still allow adequate working room? I'm basically trying to lose as little cabinet space to plumbing as possible without being stupid.

What is the best placement for both supplies and the drain? My first inclination is to pull the drain up dead center along the back wall to a tee at 14-15". The supplies would be offset 4" on either side up to 18", with a tee to a dishwasher shutoff. Basically, I'd be mimicking a traditional wall configuration for a kitchen sink even though it's coming through the floor. Good idea? Should I do something else?

One trap or two? I'm fine putting in a double san-t for separate traps if that makes my life easier.

Thanks.
 

hj

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If the inspector does not like DIYers, then he is going to HATE that sanitary cross, and he should. Inspectors "inspect", they are NOT advisors, so they look and reject what they don't like and expect the installer to KNOW, or find out, the right way, NOT ask him.
 

Esobocinski

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Yes, I get that my inspector is not my educator. (That's why I'm here.) I'd like to hear at least a one-line reason from him. So it is; that's his right.

Ok, so on re-reading, I see in IRC 3005.1.1 that a pumping appliance is banned from a double san-t. I infer that a double fixture tee is probably also suboptimal though not mentioned in IRC. I'm ok with that. A single trap into a single tee is fine.

So ... rough-in placement suggestions?
 

Terry

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If you decide on two p-traps and using one vent, you can get by with a double fixture fitting. The AAV off the top.
A 2" cleanout needs to be there too.
You can also use one p-trap, and run the disposer into a baffle tee below the second sink.

I would give yourself some room in the back. Does your cabinet go to the wall? Many don't.
 

Esobocinski

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The cabinet that is specified has a full 24" depth. It has a full back; it isn't open so that you can see the wall. However, we haven't ordered it yet. If it makes sense to change the cabinet, we can still do that. It's semi-custom; we have options.

Part of what I'm asking is how far from the studs "some room in the back" might be to a tidy experienced plumber, or any other layout advice. I'm getting the impression from reading online that trying to center the drain laterally or putting hot and cold on either side of the drain isn't necessarily considered "best" anymore.
 

JohnfrWhipple

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I have 2"x6" exterior walls and I ran my 2" waste line through the wall. I failed inspection from the structural engineer because we drilled the holes for the pipe. I had to go back and add another 2"x4" stud to sister each drilled stud and we installed those on the flat. The 2" drain line allowed me to run the waste line over 5' to get around the window and up with a vent. Later we spray foamed the entire wall.

The 2" drain line serves a large farm sink, our dishwasher and the ACO pot filler drain.

No sure what a AAV is but if you are worried about drilling holes in those walls then maybe check with your engineer if adding another 2"x4" might open this up as an option.
 

Cacher_Chick

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I am not clear on what structure you have preventing you from going into the wall. The trap arm can run inside the cabinet to a stack in the wall on either side of the window. This prevents from having to drill the structural support for the window. The DVW is not highly susceptible to freezing, as the trap is the only thing that should ever hold water.
The supply piping can come up on the inside of the wall insulation, and even if you come up through the floor, takes up a miniscule amount of space in the cabinet.
 
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