Cal. Health and Safety Code § 17958.12

(a) The Legislature hereby finds and declares the following: (1) Building officials, pursuant to this code and the California Building Standards Code, have broad authority as part of their enforcement authority to render interpretations of the code and to adopt policies and procedures to clarify the application of its provisions. (2) A building official has the discretion to apply the building standards that were in effect at the time a residential unit was constructed. This is permissible under the authority to grant modifications on a case-by-case basis and the authority of a building department to approve a material, appliance, installation, device, arrangement, or method if it finds that the design is satisfactory and equivalent to the building standards code. Several jurisdictions were not aware of this existing authority. (3) It is the intent of the Legislature to clarify that when a building permit for a residential unit does not exist, the appropriate enforcement official may make a determination of when a residential unit was constructed and then apply the California Building Standards Code and other specified rules and regulations in effect when the residential unit was determined to be constructed for purposes of issuing a building permit for the residential unit. (b) The department shall propose the adoption of a building standard to the California Building Standards Commission pursuant to Chapter 4 (commencing with Section 18935) of Part 2.5 of Division 13 to authorize, when a record of the issuance of a building permit for the construction of an existing residential unit does not exist, a local enforcement official to determine the date of construction of that residential unit, apply this part, the building standards in the California Building Standards Code, and other specified rules and regulations in effect on that date of construction to that residential unit, and issue a retroactive building permit for that construction. This authorization shall be consistent with the findings and declarations of subdivision (a). (c) This section is declaratory of existing law.