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

11B-809.10.5.1 Clear floor space.

A clear floor space 30 inches (762 mm) minimum by 48 inches (1219 mm) minimum shall be located with the long edge of the clear floor space parallel to the side of the bathtub or bathtub-shower combination. Controls shall be located on the wall at the foot of the bathtub. The edge of the clear floor space shall be flush with the control wall surface. The area under a lavatory, located at the control end of the tub, shall be permitted to encroach on the clear floor space provided the lavatory is 19 inches (483 mm) maximum in depth, and knee and toe clearance complying with Section 11B-306 is provided. Cabinets under lavatories and toilets shall not encroach on the clear floor space.