For a 2-1/2 inch building drain with a 1/4 inch slope per foot, what is the maximum number of dfu allowed to be connected?

To determine the maximum number of drainage fixture units (dfu) that can be connected to a 2-1/2 inch building drain with a 1/4 inch slope per foot, it is important to reference the plumbing code or standards, which specify how many dfu a particular drain size can accommodate.

A 2-1/2 inch building drain is often permitted a certain capacity in terms of dfu due to its diameter and the slope applied. The slope of 1/4 inch per foot is a standard and effective drainage slope that helps facilitate proper wastewater flow, ensuring that solids do not settle and block the drain.

For a 2-1/2 inch building drain, the plumbing code indicates that it can typically handle up to 24 dfu under normal circumstances, taking into account the diameter, slope, and other design considerations. Therefore, the correct answer of 24 dfu reflects the maximum that can be safely and effectively connected to that size drain.

The other options suggest fewer or more dfu than what is typically permissible for this size drain with the given slope. This reinforces the importance of knowing specific plumbing code guidelines when planning or inspecting residential plumbing systems.