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

11B-233.3.4.3 Alterations to residential dwelling units with adaptable features.

The building standards for residential dwelling units with adaptable features do not apply to the alteration, repair, rehabilitation or maintenance of residential dwelling units constructed for first occupancy on or prior to March 13, 1991. Multifamily dwelling units with adaptable features constructed for first occupancy after March 13, 1991 shall be maintained in compliance with the accessibility standards in effect at the time of construction.

Exception: Where any portion of a building’s exterior is preserved, but the interior of the building is removed, including all structural portions of floors and ceilings and a new building is constructed behind the existing exterior, the building is considered a new building for determining the application of this chapter.