Cal. Health & Safety Code § 19851

(a) The official copy of the plans maintained by the building department of the city or county provided for under Section 19850 shall be open for inspection only on the premises of the building department as a public record. The copy may not be duplicated in whole or in part except (1) with the written permission, which permission shall not be unreasonably withheld as specified in subdivision (f), of the certified, licensed or registered professional or his or her successor, if any, who signed the original documents and the written permission of the original or current owner of the building, or, if the building is part of a common interest development, with the written permission of the board of directors or governing body of the association established to manage the common interest development, or (2) by order of a proper court or upon the request of any state agency.
(b) Any building department of a city or county, which is requested to duplicate the official copy of the plans maintained by the building department, shall request written permission to do so from the certified, licensed, or registered professional, or his or her successor, if any, who signed the original documents and from (1) the original or current owner of the building or (2), if the building is part of a common interest development, from the board of directors or other governing body of the association established to manage the common interest development.
(c) The building department shall also furnish the form of an affidavit to be completed and signed by the person requesting to duplicate the official copy of the plans, which contains provisions stating all of the following:
1. (1) That the copy of the plans shall only be used for the maintenance, operation, and use of the building.
2. (2) That drawings are instruments of professional service and are incomplete without the interpretation of the certified, licensed, or registered professional of record.
3. (3) That subdivision (a) of Section 5536.25 of the Business and Professions Code states that a licensed architect who signs plans, specifications, reports, or documents shall not be responsible for damage caused by subsequent changes to, or use of, those plans, specifications, reports, or documents where the subsequent changes or uses, including changes or uses made by state or local governmental agencies, are not authorized or approved by the licensed architect who originally signed the plans, specifications, reports, or documents, provided that the architectural service rendered by the architect who signed the plans, specifications, reports, or documents was not also a proximate cause of the damage.
(d) The request by the building department to a licensed, registered, or certified professional may be made by the building department sending a registered or certified letter to the licensed, registered, or certified professional requesting his or her permission to duplicate the official copy of the plans and sending with the registered or certified letter, a copy of the affidavit furnished by the building department which has been completed and signed by the person requesting to duplicate the official copy of the plans. The registered or certified letters shall be sent by the building department to the most recent address of the licensed, registered, or certified professional available from the California State Board of Architectural Examiners.
(e) The governing body of the city or county may establish a fee to be paid by any person who requests the building department of the city or county to duplicate the official copy of any plans pursuant to this section, in an amount which it determines is reasonably necessary to cover the costs of the building department pursuant to this section.
(f) The certified, licensed, or registered professional’s refusal to permit the duplication of the plans is unreasonable if, upon request from the building department, the professional does either of the following:
1. (1) Fails to respond to the local building department within 30 days of receipt by the professional of the request. However, if the building department determines that professional is unavailable to respond within 30 days of receipt of the request due to serious illness, travel, or other extenuating circumstances, the time period shall be extended by the building department to allow the professional adequate time to respond, as determined to be appropriate to the individual circumstance, but not to exceed 60 days.
2. (2) Refuses to give his or her permission for the duplication of the plans after receiving the signed affidavit and registered or certified letter specified in subdivisions (c) and (d).