2019 California Standards for Accessible Design Guide (effective January 1, 2020 with July 1, 2021 amendments)

11B-809.10.6.4 Reinforcement for grab bars.

Reinforcement for grabs bars shall comply with the following: Continuous reinforcement shall be installed in the walls of showers 30 inches (762 mm) maximum to 38 inches (965 mm) minimum above the finish floor. The grab bar reinforcement shall be 8 inches (203 mm) minimum in height. Glass-walled shower stalls shall provide reinforcement for installation of floor-mounted or ceiling-mounted grab bars.

FIGURE 11B-809.10.6.4 REINFORCEMENT FOR GRAB BARS.