Gov. Code, § 66323

(a) Notwithstanding Sections 66314 to 66322, inclusive, a local agency shall ministerially approve an application for a building permit within a residential or mixed-use zone to create any of the following units, or any combination of the following units:

(1) One accessory dwelling unit and one junior accessory dwelling unit per lot with a proposed or existing single-family dwelling if all of the following apply:

(A) The accessory dwelling unit or junior accessory dwelling unit is within the proposed space of a single-family dwelling or existing space of a single-family dwelling or accessory structure and may include an expansion of not more than 150 square feet beyond the same physical dimensions as the existing accessory structure. An expansion beyond the physical dimensions of the existing accessory structure shall be limited to accommodating ingress and egress.

(B) The space has exterior access from the proposed or existing single-family dwelling.

(C) The side and rear setbacks are sufficient for fire and safety.

(D) The junior accessory dwelling unit complies with the requirements of Article 3 (commencing with Section 66333).

(2) One detached, new construction, accessory dwelling unit that does not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling. A local agency may impose the following conditions on the accessory dwelling unit:

(A) A total floor area limitation of not more than 800 square feet of livable space.

(B) A height limitation as provided in subparagraph (A), (B), or (C) of paragraph (4) of subdivision (b) of Section 66321, as applicable.

(3) (A) Multiple accessory dwelling units within the portions of existing multifamily dwelling structures that are not used as livable space, including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with state building standards for dwellings.

(B) A local agency shall allow at least one accessory dwelling unit within an existing multifamily dwelling and shall allow up to 25 percent of the existing multifamily dwelling units.

(4) (A) (i) Multiple accessory dwelling units, not to exceed the number specified in clause (ii) or (iii), as applicable, that are located on a lot that has an existing or proposed multifamily dwelling, but are detached from that multifamily dwelling and are subject to a height limitation in subparagraph (A), (B), or (C) of paragraph (4) of subdivision (b) of Section 66321, as applicable, and rear yard and side setbacks of no more than four feet.

(ii) On a lot with an existing multifamily dwelling, not more than eight detached accessory dwelling units. However, the number of accessory dwelling units allowable pursuant to this clause shall not exceed the number of existing units on the lot.

(iii) On a lot with a proposed multifamily dwelling, not more than two detached accessory dwelling units.

(B) If the existing multifamily dwelling has a rear or side setback of less than four feet, the local agency shall not require any modification of the existing multifamily dwelling as a condition of approving the application to construct an accessory dwelling unit that satisfies the requirements of this paragraph.

(b) A local agency shall not impose any objective development or design standard that is not authorized by this section upon any unit that meets the requirements of any of paragraphs (1) to (4), inclusive, of subdivision (a).

(c) A local agency shall not require, as a condition for ministerial approval of a permit application for the creation of an accessory dwelling unit or a junior accessory dwelling unit, the correction of nonconforming zoning conditions.

(d) The installation of fire sprinklers shall not be required in an accessory dwelling unit or a junior accessory dwelling unit if sprinklers are not required for the primary residence. The construction of an accessory dwelling unit or a junior accessory dwelling unit shall not trigger a requirement for fire sprinklers to be installed in the existing multifamily dwelling.

(e) A local agency shall require that a rental of the accessory dwelling unit created pursuant to this section be for a term longer than 30 days.

(f) A local agency may require, as part of the application for a permit to create an accessory dwelling unit connected to an onsite wastewater treatment system, a percolation test completed within the last five years, or, if the percolation test has been recertified, within the last 10 years.