Plumbing Fixtures and Fixture Fittings
What this domain tests
Fixture selection, fixture-unit values, water consumption limits, setting dimensions, trap and trap-arm rules, and backflow protection at the fixture.
Core rules
- Consumption limits carried into code: water closets 1.6 gallons per flush, urinals 1.0 gpf, showerheads 2.5 gpm at 80 psi, kitchen faucets 2.2 gpm, public lavatory faucets 0.5 gpm per cycle.
- Clearances: a water closet needs 15 inches from centerline to any sidewall and 21 inches of clear space in front; a lavatory needs 15 inches centerline to wall.
- Every fixture not specifically exempt needs a trap with a 2- to 4-inch water seal; S-traps and crown-vented traps are prohibited because they siphon.
- Trap-arm length is limited by trap size (about 5 feet for 1¼ inch, 6 feet for 1½ inch, 8 feet for 2 inch) and the arm must slope uniformly to the drain.
- Backflow protection at the fixture: vacuum breakers on hose bibbs and hand showers, air gaps at food-service sinks and water treatment, flushometer valves protected against cross-connection.
- Drainage fixture units: a bathroom group of water closet (3 dfu), lavatory (1 dfu), and tub/shower (2 dfu) totals 6 dfu.
Worked example
Three identical bathroom groups tie into one horizontal branch: 3 × 6 = 18 dfu. A 2-inch branch carries only 6 dfu, so it fails. A 3-inch branch handles 20 dfu, so the correct call is a 3-inch branch with individual 1½- and 2-inch fixture drains.
Traps that cost marks
Counting a bathtub and shower separately when they are one combination fixture; ignoring the 21-inch front clearance; sizing the branch on the largest single fixture instead of total dfu; using an air admittance valve where the code requires a real vent.