Piping, Materials, Joints, and Water/Drainage System Installation
Materials, joints, and support
UPC piping must be approved for the intended service. Match pipe, fittings, and joining method: PVC and ABS use solvent cement per manufacturer; no-hub cast iron uses listed couplings with a shield; copper joints follow the listed solder/brazing standard; transition between dissimilar metals with a dielectric fitting or approved isolation. Potable water piping must not use lead-based solder. Support spacing, hangers, and protection from freezing, corrosion, and structural damage must follow the code and manufacturer instructions.
Drainage, vents, and water lines
- Gravity drainage must slope in the direction of flow. Under common UPC rules, 2-1/2-inch and smaller pipe slopes at 1/4 inch per foot; 3-inch through 6-inch pipe may slope at 1/8 inch per foot. Less slope than required risks solids settling.
- Traps must be vented, and trap arms must stay within the allowed length for their size. Vents must terminate properly and cannot be used as a drain.
- Cleanouts are required at the base of stacks, at changes of direction over 45 degrees, and other code locations; they must remain accessible.
- Water supply lines need backflow protection, freeze protection, and pressure testing before concealment.
Worked example
A 3-inch PVC building drain runs 20 feet at the minimum allowed slope. For 3-inch pipe, use 1/8 inch per foot: 20 ft × 1/8 in/ft = 2.5 inches of fall. If the layout provides only 1 inch of fall, the slope is about 1/20 inch per foot, below the minimum, so the drain must be redesigned. Do not use 1/4 inch per foot as the “only” legal slope for 3-inch pipe; the code allows the smaller minimum, but the pipe still must drain.
Traps that cost marks
- Mixing PVC cement and ABS fittings.
- Using a shielded coupling on pressure pipe or a solvent-welded joint on no-hub cast iron.
- Measuring slope from the wrong end or ignoring fitting make-up.
- Concealing a cleanout or vent terminal.
- Testing with air where water is required, or skipping the test.