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

The CBC 11B-504.4.1 requirement for contrasting stripes is not included in 2010 ADA Standards. It should be noted that CBC Chapter 10 has a different requirement for contrasting stripes at stepped aisles in Assembly occupancies (not adopted by DSA-AC, as this is a life safety requirement, not an accessibility requirement), as follows:          

1029.13.2.3 Tread contrasting marking stripe.  A contrasting marking stripe shall be provided on each tread at the nosing or leading edge such that the location of each tread is readily apparent when viewed in descent.  Such stripe shall be not less than 1 inch (25 mm), and not more than 2 inches (51 mm) wide.

Exception:  The contrasting marking stripe is permitted to be omitted where tread surfaces are such that the location of each tread is readily apparent when viewed in descent.

Where differing requirements apply, it is compulsory to comply with both, if possible. Where CBC Subsection 1029.13.2.3 applies, it is possible to comply with it and Subsection 11B-504.4.1 by providing contrasting stripes at each tread that are exactly 2 inches wide, located not more than 1 inch from the nosing. Where the Exception at Subsection 1029.13.2.3 applies, contrasting striping at the upper approach and bottom tread are still required to comply with Subsection 11B-504.4.1 at interior stepped aisles, and at the upper approach and all treads at exterior stepped aisles (see scoping requirement at 11B-210.1, Exception 3.