Cal. Pub. Util. Code § 780.5
The commission shall require every residential unit in an apartment house or similar multiunit residential structure, condominium, and mobilehome park for which a building permit has been obtained on or after July 1, 1982, other than a dormitory or other housing accommodation provided by any postsecondary educational institution for its students or employees and other than farmworker housing, to be individually metered for electrical and gas service, except that separate metering for gas service is not required for residential units which are not equipped with gas appliances requiring venting or are equipped with only vented decorative appliances or which receive the majority of energy used for water or space heating from a solar energy system or through cogeneration technology.
Ca. Pub. Util. Code § 780.5