What size drain is required for a washing machine?

Question

What is the plumbing Code for Washing Machine Drain?

I want to install an extra washer and dryer in my detached two car garage.

This is a picture from a house under construction.

I believe the Drain is 2 inches. Then it appears to be upsized to a 3 inch PVC in the crawlspace.

Answer 1

You're correct, the requirement for washing machine drain is 2".

To determine if you have enough drain capacity for an additional machine, you need to consult the Uniform Plumbing Code's Drainage Fixture Unit values and ensure the total fixtures don't exceed the capacity of the drain for your laundry room (or plan an upgrade.)

These tables should help get you started:

• Fixture values https://www.engineeringtoolbox.com/drainage-fixture-unit-values-d_1077.html
• Drain capacity per pipe size in stacks & branches https://www.engineeringtoolbox.com/drainage-fixture-units-piping-load-d_1078.html