Plumbing Fixtures and Fixture Fittings
Fixture requirements
Know the occupancy-based minimum fixture table, accessibility clearances, and the flow and flush limits on fittings. Typical limits: water closets 1.6 gpf maximum, urinals 1.0 gpf, showerheads 2.5 gpm at 80 psi. Every fixture is individually trapped except where the code expressly allows otherwise; the trap seal is 2 to 4 in., the trap must be level and self-cleaning, and it needs an accessible cleanout plug. Floor drains need trap primers where the seal could evaporate.
Fixture fittings
Shower and tub/shower valves must be pressure-balanced or thermostatic with a temperature-limiting device. Hose bibbs and sillcocks require vacuum breakers. Flushometer valves need about 15 psi residual pressure at the fixture, compared with 8 psi for gravity flush-tank closets. Sinks, lavatories, and drinking fountains need strainers or guards where the code requires them, and fixtures used for food or handwashing must deliver hot and cold water.
Traps in questions
- Do not confuse drainage fixture units (DFU) with water-supply fixture units (WSFU); they come from different tables and are never summed together.
- Trap size follows the fixture outlet; installing a larger trap is not an upgrade and can violate the code.
- Double trapping and S-traps are prohibited - the trap arm slope is fixed, not bent to fit the room.
- Compartment and clearance dimensions are measured to finished surfaces.
Worked example
A plan shows a 2 in. trap arm running 9 ft to its vent. At 1/4 in./ft the allowable trap-to-vent distance for 2 in. is 8 ft, so the layout fails even though the trap itself is correct.