One of the bathroom jobs we do most is the one in our Instagram post about "the tub you never use": the old tub comes out and a fully custom walk-in shower goes in. The homeowner in that post wanted a cleaner, safer, more modern bathroom.
What follows is what the building code asks of the new shower. Phoenix builds to the 2024 International Residential Code (IRC), part of the 2024 Phoenix Building Construction Code that took effect on August 1, 2025. Other Valley cities adopt their own editions, so the details can differ by city.
The shower has a minimum size
A shower compartment needs at least 900 square inches of floor inside and at least 30 inches across at its narrowest (IRC P2708.1). Both are measured from the finished walls, at the height of the threshold, and the space has to stay that size up to 70 inches above the drain.
Because it is measured from the finished surface, the backer board and the tile count against it. In a tight alcove that is worth checking before the walls go up. The same section also says hinged shower doors open outward.
The curb, and the slope to the drain
Where a shower has a curb, the code sets its height: 2 to 9 inches from the top of the curb down to the top of the drain, and the curb at least an inch lower than the sides and back of the shower floor (IRC P2709.1).
The floor slopes evenly to the drain, at 2 to 4 percent: a quarter of an inch to half an inch for every foot. That slope is what keeps water in the shower once the tub's high sides are gone.
The valve holds the temperature
An old tub often has a two-handle faucet. The new shower valve has to be a pressure-balancing, thermostatic or combination valve, and it has to be set so the water can't come out hotter than 120°F (IRC P2708.4). It keeps the temperature steady when someone flushes a toilet or runs a tap elsewhere in the house.
Glass near water is a hazardous location
Glass in the walls or enclosure of a shower or tub is a hazardous location when its bottom edge is less than 60 inches above the floor you stand on (IRC R324.4.5). Glazing in hazardous locations, mirrors included, has to pass the impact test the code points to, CPSC 16 CFR 1201 (IRC R324.3). Shower doors and panels are made to that test, which is worth confirming for any glass you choose.
Walls that stay dry
The shower floor and walls need a nonabsorbent finish, and on the walls it runs at least 6 feet above the floor (IRC R327.2). Tile on a proper backer, or a solid surface panel, is what usually goes there.
What this means for your bathroom
A conversion is more than pulling a tub. The size, the slope, the valve, the glass and the wall finish all have rules, and the drain and supply lines move with them, which is licensed plumbing work. If you are thinking about one, we can look at the space with you and talk it through.
Sources
- 2024 IRC, Chapter 27 Plumbing Fixtures: P2708.1, P2708.4, P2709.1, P2710.1, International Code Council
- 2024 IRC, Chapter 3 Building Planning: R324.3, R324.4.5, R327.2, International Code Council
- Phoenix Building Construction Code, City of Phoenix
