Plumbing Fixtures and Fixture Fittings
What questions target
Fixture questions test whether you know the installation requirements - spacing, clearance, support, sealing, backflow protection, and accessibility - not just the fixture's name.
Spacing and clearance
Water closets are conventionally set with the centerline at least 15 inches from a side wall or partition and at least 15 inches from the centerline of an adjacent fixture, in a compartment at least 30 inches wide. Lavatories need similar side clearance. Accessible fixtures add reach-range, knee-clearance, and turning-space rules that frequently appear in exam scenarios involving a remodel.
Connections and protection
- Each fixture gets its own trap, sized to the fixture outlet.
- Supply stops must be accessible.
- Hose bibbs and sillcocks need vacuum-breaker protection.
- Fixture outlets must not be obstructed; escutcheons and sealing at wall/floor penetrations are required.
- Floor drains need trap primers, especially in rooms with mechanical equipment.
- Shower and tub/shower valves need scald-limiting (pressure-balancing or thermostatic) protection.
Water efficiency
Modern water closets are commonly 1.28 gpf; urinals and lavatories have their own maximums. Retrofitting an old fixture with a new flush valve must respect the fixture's rated flush volume.
Worked example
A 30-inch-wide alcove with a wall on one side: the water closet centerline must be 15 in from that wall, so the fixture's center sits at 15 in in a 30 in space - exactly minimum. Any structural furring that narrows the space makes it noncompliant.
Traps
Forgetting accessibility clearances on remodels; installing a fixture without a trap primer at a floor drain; and omitting vacuum breakers on hose connections.