Section 701.1/Drainage System Design
UPC 701 covers sanitary drainage system design using DFU with sizing tables specific to the Uniform Plumbing Code.
Sanitary drainage piping must be sized based on the total drainage fixture unit (DFU) load from all connected fixtures per the UPC fixture unit tables. Horizontal drainage piping must be installed at a minimum slope of 1/4 inch per foot for pipes 3 inches and smaller, and 1/8 inch per foot for pipes 4 inches and larger. Cleanouts must be provided at every change of direction greater than 45 degrees, at the upper terminus of every horizontal drain, and at intervals not exceeding 100 feet for pipes 4 inches and larger. All drainage piping must be supported at the intervals specified in Table 314.1.
Why this section exists
A sanitary drainage system relies on gravity to move waste and water from fixtures to the building sewer. Pipes that are too small cause backups and overflows. Pipes with insufficient slope allow solids to settle and accumulate, creating blockages. Cleanouts provide access for maintenance and clearing blockages without cutting into the piping. The UPC drainage system requirements work together to create a system that drains reliably for the life of the building.
What plan reviewers look for
Plan reviewers check the plumbing isometric or plan for pipe sizes at each segment. They verify sizes against the DFU load from connected fixtures. They check that horizontal runs have the minimum slope noted. They verify cleanout locations at direction changes, building drain origins, and at the maximum interval spacing. They check that the building drain connects to the building sewer at the correct elevation.