Washing machine pipe sizes

[Johnny_b]

I am having a new house built. Plumbing has been roughed in for under slab. I’m wondering if the pipe in red should be 3” or 2”. My area has adopted IPC code up to 2012 edition. Thank you

 

[Reach4]

2-inch is ok, and much more common.

 

[Sponsor]

 

[Johnny_b]

even with a new age washer? Seems the code reads it must dump into a 3" after the trap.

 

[Reach4]

even with a new age washer? Seems the code reads it must dump into a 3" after the trap.

I am not a plumber.

IPC 2012 802.4 says

802.4 Standpipes. Standpipes shall be individually trapped.
Standpipes shall extend not less than 18 inches (457 mm) but
not greater than 42 inches (1066 mm) above the trap weir.
Access shall be provided to all standpipes and drains for rod-
ding.
​

And then

406.2 Waste connection. The waste from an automatic
clothes washer shall discharge through an air break into a
standpipe in accordance with Section 802.4 or into a laundry
sink. The trap and fixture drain for an automatic clothes
washer standpipe shall be not less than 2 inches (51 mm) in
diameter. The fixture drain for the standpipe serving an auto- 1
matic clothes washer shall connect to a 3-inch (76 mm) or I
larger diameter fixture branch or stack. Automatic clothes |
washers that discharge by gravity shall be permitted to drain
to a waste receptor or an approved trench drain.
​

I suspect that means that after the WM water joins other waste, that must be 3 inch or more. But I could be wrong.

 

[wwhitney]

Indeed, from Chapter 2 Definitions of the 2012 IPC:

FIXTURE DRAIN. The drain from the trap of a fixture to a junction with any other drain pipe.

FIXTURE BRANCH. A drain serving two or more fixtures that discharges to another drain or to a stack.

STACK. A general term for any vertical line of soil,waste, vent or inside conductor piping that extends through at least one story with or without offsets.

Cheers, Wayne