Cal. Health & Safety Code § 17959.5

The housing appeals board may, upon appeal or upon application by the owner, grant variances from local use zone requirements in order to permit an owner-occupant of a dwelling to construct an addition to a dwelling to meet occupancy standards relating the number of persons in a household to the number of rooms or bedrooms. This power of the housing appeals board shall be in addition to, and shall not otherwise affect, the powers of other governmental boards and agencies to allow local use zone variances.