Plumbing Question

[Robert Olin]

I'm roughing in the plumbing for my two story house before pouring the slab. The downstairs bathroom will have a toilet, laundry sink, clothes washer drain and shower. Everything drains to the 3" main under the slab. Question: Can I combine the laundry sink 2" drain, with the clothes washer drain shower drain or should it have it's own 2" pipe going to the 3"?

Thanks, Bob

[Wayne Whitney]

According to my copy of Code Check from a few years ago:

Under the UPC, clothes washers count as 2 fixture units, showers as 3 fixture units, and laundry tubs as 2 fixture units. A horizontal 2" drain can handle 8 fixture units. So you could drain all three with a single 2" line. Of course, everything has to be properly vented.

Under the IRC, the 2" horizontal drain can only handle 6 fixture units, but the shower only counts as 2 fixture units, so the 2" horizontal line is still OK.

Cheers, Wayne