What is the minimum required size for a trap arm serving a clothes washer standpipe?

• A. 1 inch
• B. 1 ½ inches
• C. 2 inches
• D. 3 inches

Answer: (C)

The minimum required size for a trap arm serving a clothes washer standpipe is 2 inches. This dimension is specified in plumbing codes to ensure adequate drainage and to prevent issues such as clogs or slow drainage that can occur with smaller diameters.

A trap arm connects the trap to the drain, and its size is crucial for allowing sufficient flow of water and waste from the washing machine. A 2-inch diameter provides the necessary volume and minimizes the risk of backups, which can be particularly problematic given the high volume of water discharged by washing machines during operation. The larger diameter allows for a more effective and efficient drainage system that can accommodate the peak flow rates associated with washing machines.

A smaller diameter, such as 1 inch or 1½ inches, would not support the necessary flow volume and could lead to issues that affect the performance of the drainage system. Thus, using a 2-inch trap arm is essential for maintaining optimal function and compliance with plumbing code requirements.