Laundry Washer/Sink Code Question

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Patrick75

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I'm rouging in for a washing machine and laundry tub in my garage. IPC code says:

"The trap and fixture drain for an automatic clothes washer standpipe shall be a minimum of 2 inches (51 mm) in diameter. The automatic clothes washer fixture drain shall connect to a branch drain or drainage stack a minimum of 3 inches (76 mm) in diameter."

I'm unclear about the specific definition of "fixture drain" and "branch drain." Do I have to transition from 2" to 3" immediately after the vent or where the laundry tub ties in to the drain pipe from the washer or can I do it at some later point? I'll be tying into my 3 inch main drain line in the crawl space about 30 feet from the washer. I was planning to transition to 3" for the 25' in the crawl space, but was hoping to stick with 2" for the part inside the garage so it would fit in the wall.

Is there an alternate way to plumb a washer and a sink under IPC avoiding the 3"? [eta: nm, i see 802.4.3.1. Not sure I want to do that, but would appreciate clarification about where I have to transition to 3" if I use 2 traps.]
 
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Jeff H Young

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That's the way I understood the code but I think a member here that's usually active Wayne said there has been some change perhaps it was just places that have IRC but hope he sees this and Replies
 

wwhitney

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The first point is to check whether the IPC applies to a residential install. The quoted section is not in the IRC, and in states that have adopted the P (plumbing) chapters of the IRC, those take precedence over the IPC when applicable.

Up.codes says that NC has adopted Chapter 27 of the IRC, and it looks like they amended P2718:


I guess it is saying that any horizontal pipe carrying the washer drainage needs to be 3", but verticals can be 2". So your plan is fine.

As to your underlying question, see the definitions in Chapter 2. A fixture drain is a drain carrying the output of just one fixture, and a branch drain is a drain carrying the output of 2 or more fixtures. So the branch drain begins at the wye or tee where the two fixture drains combine.

Cheers, Wayne
 

Patrick75

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The first point is to check whether the IPC applies to a residential install. The quoted section is not in the IRC, and in states that have adopted the P (plumbing) chapters of the IRC, those take precedence over the IPC when applicable.

Up.codes says that NC has adopted Chapter 27 of the IRC, and it looks like they amended P2718:


I guess it is saying that any horizontal pipe carrying the washer drainage needs to be 3", but verticals can be 2". So your plan is fine.

As to your underlying question, see the definitions in Chapter 2. A fixture drain is a drain carrying the output of just one fixture, and a branch drain is a drain carrying the output of 2 or more fixtures. So the branch drain begins at the wye or tee where the two fixture drains combine.

Cheers, Wayne
Oh cool, so the 3" branch drain isn't code in NC? To be clear, it's almost all horizontal. I don't really have a vertical stack (1 story house with crawlspace. The only vertical section is about 2 feet long coming down from the garage into the crawlspace.

The waste from an automatic clothes washer shall connect to a vertical drain of not less than 2 inches (51 mm) in diameter, or a horizontal drain of not less than 3 inches (76 mm) in diameter.

[eta: re-reading, if the place where the sink drain joins the washer drain is considered a horizontal drain, then I guess it has to be 3", not 2". Is that right?]
 
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wwhitney

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Depends on how you join the sink and the washer. If you want to avoid vertical 3", I would do washer trap -- 2" trap arm -- 1-1/2" vent takeoff - 2" fixture drain turns down -- sink joins on the 2" vertical -- 3" LT 90 elbow to go horizontal in the crawl space (with 3x2 bushing in the top).

Or if you need a little offset getting into the crawl space, you can do: sink joins on the 2" vertical -- 2" 45 to go diagonal - 3" 45 to go horizontal in the crawl space (with 3x2 bushing in the inlet).

Cheers, Wayne
 

Patrick75

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I'm trying to find some pictures of an actual 802.4.3.1 rough in. I know that the standpipe and sink tailpiece have to be < 30" apart horizontally, but can the actual pipes connecting them be longer than 30" total? For connecting the sink to the trap-less arm, would I just use the elbow piece from my sink trap kit?
 

wwhitney

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I would take the 30" limitation as measured along the path of the sink horizontal tailpiece.

How about a photo or diagram of the area? Is the problem with separate traps that the place where you can go horizontal in the crawl space is not close to where you want the standpipe?

Cheers, Wayne
 

Patrick75

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I would take the 30" limitation as measured along the path of the sink horizontal tailpiece.

How about a photo or diagram of the area? Is the problem with separate traps that the place where you can go horizontal in the crawl space is not close to where you want the standpipe?

Cheers, Wayne
It's one of the problems. Along the back wall of the garage, from left to right is the washer, dryer, sink, water heater, then the entry point into the crawl space. It's probably about 8 feet inside the garage and then 25 ft in the crawlspace to the main. I'm having a hard time picturing how to do the actual rough in and a harder time finding pictures of actual rough ins using the shared standpipe/trap. Does the connection between the sink drain and the standpipe have to be a straight piece of pipe, or can I go back into the wall and then across to the standpipe? Does the total length of pipe have to be under 30" or just the horizontal distance?

Is this 802.4.3.1 thing something that people really do, bc I can't seem to find any pictures of it other than drawings. Maybe I'm being silly and should just make the 3" fit.
 

wwhitney

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So can't you do something like the elevation drawing below? Blue is 2", Green is 1.5" (sink trap arm and vent), and red is 3". The circle means the pipe turns out of the wall (for the laundry sink trap connection).

A trap arm can't fall more than one pipe diameter while it must fall at least 1/4" per foot. So if you achieve the exact minimum fall, a 2" trap arm (laundry standpipe) can be up to 8' long, and a 1-1/2" trap arm (laundry sink) can be up to 6' long.

A 3" CO just inside the garage (not shown) would be a good idea or perhaps required (I'm not up on those rules).

Cheers, Wayne

laundry.jpg
 

Patrick75

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Yea, I can do that. I was hoping to use 2" pipe in the penetration between the garage and crawlspace, but what's an extra inch I guess... Question, this arrangement would be a wet vent, which isn't allowed here, right? I was planning something like the following picture (not my picture), except upsizing to 3" where the sink joins in, 2" for the washer, and 1-1/2 for everything else (and it looks like they incorrectly used a sanitary tee horizontally for the washer trap vent.
 

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wwhitney

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IPC allows "common venting at different levels" which is basically vertical wet venting for any 2 fixtures (limit 2).

[IPC also allows a san-tee on its back for a vent takeoff on a horizontal trap arm, but a combo is better if you have room.]

The advantage of the wet venting arrangement I drew is that where the drain is carrying both the sink and the clothes washers, it's 2" only on the vertical, and becomes 3" on the horizontal.

If you are able to move the vent stack close enough to the crawl space (depends on the trap arm length limits), and you have enough vertical height available, you could use the section of 2" branch drain at a 45 to go into the crawl space, so all the 3" is limited to the crawl space. But based on what you've said so far, it would probably be easier to bring the 3" into the first stud bay (and add a 3" cleanout).

Cheers, Wayne
 

Patrick75

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Oh cool, well that makes things easier. Out of curiosity, why do I find so many pictures of rough-ins with separate vents (like my picture)? Is that a UPC requirement? Any idea what the justification is for requiring the upsizing to 3"? It seems unlikely to me that with a high-efficiency washer and a laundry sink that there'd be enough water draining to necessitate 3" when the main serving the entire house is only 3".
 

wwhitney

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Separate vents would just sort of be the default and give you more flexibility in layout. The UPC would allow wet venting a laundry sink over a washing machine, but the wet vent would have to be 3", so it's not as practical.

As to why the IPC has the 3" requirement about washing machines (amended in your case), I'm not sure. Maybe they think the pumped discharge of the washer is going to be problematic compared to gravity draining fixtures.

Cheers, Wayne
 
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