Clothes Washer drain size

[DavidTu]

I apparently mistakenly sized my clothes washer drain based on dfu's, unaware of the special requirement in UPC calling for a 3" drain. I've seen discussion elsewhere saying that enforcement and interpretation of this vary widely inspector to inspector, region to region. I'm in Seattle WA and wondering how I will likely fare with the inspector.

Here is the setup: 2" trap & fixture arm going to 2" horzontal drain, which picks up a laundry sink and two lavs before going into a few feet of 3" pipe then 4" pipe on the horizontal and on down the stack.

Thanks in advance.

[Gary Swart]

From your description, you are just fine. You need a 2" standpipe for new washers which you have and then it increases in size and that too is just fine.

[DavidTu]

From your description, you are just fine.

That's good to hear Gary... just to be clear, though, the horizontal 2" run (w/ 7 dfu) goes for about a total of 16' horizontal before going to 3" and 4" (horizontal for another 14' or so before vertical). Hope that doesn't change your reply.

[Gary Swart]

So long as you maintain the minimum slope of 1/4" per foot. That is required of every drain regardless of diameter of the pipe.

[shacko]

I hope we have a vent somewhere on your hook-up?

[Inspektor Ludwig]

Are you wet venting this installation? Curious, what section of chapter 7 UPC are you referencing? I think I know which section you're talking about, the exceptions at the bottom of the DFU table. That language for 6 DFU is for laundrymats and multi-family laundry rooms where you would have a battery of clothes washers draining at the same time. It requires a 3" horizontal drain to address sudsing. Are there Inspectors that require a single family clothes washer to have a 3" drain on the horizontal? Must be Combo Inspectors because I've never heard of any Plumbing Inspector requiring that.

[Terry]

I think the 3" is an IPC thing on the East Coast.
I've always used 2" in Seattle.