Uniform Plumbing Code - Drainage, Waste and Venting
What this domain covers
This domain tests drainage slope, fixture units, traps, cleanouts, backwater protection, sumps and venting. Questions often ask whether a drain will flow properly, whether a trap is protected, or whether a cleanout is accessible.
Core rules
- Horizontal drainage pipe slopes at 1/4 inch per foot for 2 1/2-inch and smaller pipe, and 1/8 inch per foot for 3-inch and larger pipe.
- Size drainage piping by drainage fixture units from the UPC tables, not by fixture count alone. A bathroom group, kitchen sink, laundry tray and floor drain each add load.
- Each trap must be vented. Trap arms are limited in length by pipe size and slope; S-traps, crown-vented traps and double-trapped fixtures are prohibited.
- Provide cleanouts at the base of stacks, at changes of direction and at required intervals, and keep them accessible. Provide backwater valves where fixtures are subject to backflow, and properly sized sumps or interceptors where required.
- Vent every trap, terminate vents properly above the roof, and use air admittance valves only where the UPC permits them.
Worked example
A 3-inch building drain runs 60 feet at minimum slope. The required fall is 60 × 1/8 inch = 7.5 inches. If the same run were 2-inch pipe, minimum slope would be 1/4 inch per foot and fall would be 15 inches. The inspector checks the slope, the cleanout at the base of the stack, and venting before approving the rough-in.
Traps that cost marks
Using 1/4 inch per foot for 3-inch pipe; omitting a vent or installing a flat vent; treating an air admittance valve as a substitute for any required vent; blocking cleanout access; and missing a backwater valve at a below-grade fixture.