International Residential Code (IRC) Plumbing Practice Test 2025 – All-in-One Resource to Master Your Exam!

The maximum number of fixture units allowed on a 4-inch pipe with a slope of 1/4 inch per foot is determined by consulting the sizing guidelines provided in the International Residential Code (IRC) and plumbing codes regarding drainage systems. The code specifies that the capacity of a specific pipe size in terms of fixture units depends on factors like the pipe diameter, the slope, and the intended application.

For a 4-inch pipe with a slope of 1/4 inch per foot, the code specifies that this pipe can accommodate a higher number of fixture units compared to smaller diameter pipes. According to the plumbing code tables, a 4-inch pipe can support a maximum of 216 fixture units under the specified conditions.

This capacity is based on the ability of the pipe to handle both the volume of water and the flow rate that can occur within a system that has multiple fixtures connected to it. Thus, the 216 fixture unit capacity reflects the optimal performance of the piping system while managing the potential for drainage without causing blockages or overloading the system.