California Code, Health and Safety Code - HSC § 114266

(a) Each permanent food facility shall be fully enclosed in a building consisting of permanent floors, walls, and an overhead structure that meet the minimum standards as prescribed by this part. Food facilities that are not fully enclosed on all sides and that are in operation on January 1, 1985, shall not be required to meet the requirements of this section until the facility is remodeled or has a significant menu change or significant change in its method of operation.

(b) Notwithstanding subdivision (a), this section does not require the enclosure of dining areas or any other operation approved for outdoor food service.

(c) Notwithstanding subdivision (a), a produce stand that was in operation prior to January 1, 2007, shall have no more than one side open to the outside air during business hours.