What is the minimum height a standpipe for a clothes washer should be above the trap?

In plumbing for clothes washers, the minimum height a standpipe must be situated above the trap is 18 inches. This height is essential to ensure proper drainage and to prevent siphoning, which can lead to issues such as backflow or foul odors in the washer compartment. Maintaining a sufficient vertical distance from the trap allows for adequate drainage while minimizing the risk of sewer gases entering the living space. Thus, the specification of 18 inches is a critical requirement in plumbing codes to ensure both functionality and health standards in residential plumbing systems. Understanding this height requirement helps ensure that installations adhere to industry standards, promoting safe and effective operation of washing machines.