What is the minimum size of a building drain for a multi-story building?

The minimum size of a building drain for a multi-story building is established to ensure adequate capacity for the expected wastewater flow and to prevent issues such as clogs or backflow. A 4-inch diameter building drain offers a balance between structural integrity and functionality, accommodating the high volume of drainage typically experienced in multi-story applications.

Larger drains accommodate greater volumes, which is crucial in buildings with multiple floors, where multiple fixtures may discharge simultaneously. Having a drain of 4 inches ensures compliance with plumbing codes that dictate minimum requirements to maintain proper drainage and ventilation within the plumbing system, thus preventing problems that could arise from undersized systems.

The choices of smaller diameters do not provide the same level of assurance in handling the wastewater flow from a multi-story setup, making them unsuitable for this application. Choosing a drain that meets the higher demand of a multi-story building, therefore, emphasizes proper system performance and longevity.