UPC 422: How Many Plumbing Fixtures a Building Must Have

Section 422 and Table 422.1 set the minimum fixture count. The count runs off two things. The first is the occupant load, the number of people the space is built to hold. The second is the occupancy group, meaning what the space is for. An office, a restaurant, a store, and a school are each a different group. Table 422.1 lists a fixture ratio for each group. As the occupant load rises, the required number of fixtures rises with it.

The table sets separate ratios for water closets (toilets), lavatories (hand sinks), urinals, and drinking fountains. The ratios are not the same across groups. A restaurant or bar packs many people into a small floor, so it needs far more fixtures per person than a warehouse does. The code also splits the required count between the sexes:

The minimum number of fixtures shall be calculated at 50 percent male and 50 percent female based on the total occupant load.

Any fraction rounds up. A result of 1.2 toilets means you install 2.

This is a commercial rule. It comes up on every new restaurant, office, retail, or medical space. It also comes up on most tenant improvements that change the use or add people. Turn a small shop into a busy cafe and the occupant load climbs. That can push the required fixture count up too. This is why the count gets checked early, at plan review, before any walls go up.

Separate restrooms for each sex are generally required once a space passes a set occupant load. Small spaces below that load can sometimes share a single unisex restroom instead. The table and its notes set where that line falls for each type of use.

If you are planning a commercial space in Phoenix, the fixture count drives your floor plan. Restrooms need floor area, drain lines, and venting. So the count shapes the layout from day one. Guess low and plan review rejects the drawings. Guess high and you spend money and floor space you did not need.

Nail down the occupant load first, because every fixture number flows from it. Get the design team and a licensed plumber to run your numbers against Table 422.1 before you sign a lease. Restroom count can decide whether a space even works for your use. A restaurant build-out also brings grease interceptor sizing and floor drain requirements into the plan. The fixtures you install must also meet Arizona low-flow fixture rules, and public restrooms have to meet ADA commercial restroom plumbing rules on top of the count. Our commercial plumbing service can run these numbers with your design team.

UPC Section 422 and Table 422.1 are part of the Uniform Plumbing Code. IAPMO publishes and holds the copyright on them. The excerpt above reflects the rule as adopted. Exact ratios shift between code editions, so the current table is the authority, not any single number. Phoenix enforces the 2024 UPC with local amendments as part of its Building Construction Code. Read the current section on UpCodes or in the IAPMO 2024 UPC. Confirm local amendments through the City of Phoenix Planning & Development Department at phoenix.gov/pdd.