What is the minimum allowable diameter for a floor drain?

The minimum allowable diameter for a floor drain is 2 inches. This sizing is established to ensure proper drainage and to prevent blockage. A 2-inch diameter is typically adequate to handle the flow of wastewater from most floor areas in residential and light commercial settings while also accommodating debris that may enter the drain.

Using a diameter larger than the minimum can help in areas where higher flows of water are anticipated or where larger debris may be present, but the 2-inch diameter serves as a baseline in plumbing codes for standard applications. This sizing aligns with industry standards and best practices in plumbing design, ensuring efficiency in waste removal and compliance with building regulations.