Clothes Washer drain size

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.

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.

Gary Swart said:

From your description, you are just fine.

Click to expand...

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.

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.

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

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.

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