Fixtures, Fixture Fittings, and Appliances
Fixture unit values
Drainage fixture units drive sizing. Common private-residential values: water closet 3 dfu, lavatory 1, bathtub or shower 2, kitchen sink 2, floor drain 2, clothes washer standpipe 2, dishwasher 2. Public water closets count higher (often 4 dfu, or per flush valve). Supply values are given in wsfu, with flush tanks and flush valves counted separately.
Spacing and accessibility
Know the water closet compartment: 30 inches wide by 60 inches deep, with the centerline of the fixture at least 15 inches from any sidewall and 15 inches from a bathtub. Fixtures must be reachable for cleaning and repair, and fixtures in dwelling units must be provided in the required numbers. Lavatories need safe access to the trap for service.
Water efficiency and materials
Federal standards cap showerheads at 2.5 gpm, lavatory faucets at 2.2 gpm, and urinals at 1.0 gpf; Michigan's code and law require new water closets to be 1.28 gpf or less. Fixtures must be listed and installed per the manufacturer's instructions, which the code makes part of the installation requirements.
Appliances
Dishwashers need an air gap or air break before connecting to a drain. Water heaters need a temperature and pressure relief valve, piped full size, without a reducing fitting, terminating not more than 6 inches above the floor or to the exterior, with no threaded end. Clothes washers need a properly sized standpipe and trap.
Worked example
Bathroom group dfu = water closet 3 + lavatory 1 + bathtub/shower 2 = 6 dfu before adding a floor drain (2), giving 8 dfu for the branch.