13-25 Standpipe to laundry tub

Question: 13-25Code Section: 7Date: 13 December 2013OBC 2012 Reference:

Question Submitted: I wanted some insight to the following code reference that has been revised for the new 2012 OBC  ( Div B Part 7 table The trap size for clothes washers has been changed from 1 ½” to 2”. My question basically is if a plumber does not install a standpipe off the laundry tub and the discharge from the washing machine is connected indirectly into the laundry tub (Basically using the laundry tub as the stand pipe) is the laundry tub still required to use a 2” trap? Or if a laundry box is installed with a 2” trap is the laundry tub still required to have a 2” trap or is an 1 ½” sufficient ?


1) The size of the trap for the laundry tub which receives the indirectly connected washing machine drain, would be 1 ½” as per Table (item 18) if the tub is less than 3 compartments.

2) If a drain is installed to serve a laundry tub and a standpipe (aka. standing waste pipe) for a washing machine (ie. laundry box), the common p-trap and the piping that serves the stand pipe would require to be min. 2” size as per Table (item 9) See sketch.