Gov. Code, § 66321

(a) Subject to subdivision (b), a local agency may establish minimum and maximum unit size requirements for both attached and detached accessory dwelling units.

(b) Notwithstanding subdivision (a), a local agency shall not establish by ordinance any of the following:

(1) A minimum square footage requirement for either an attached or detached accessory dwelling unit that prohibits an efficiency unit.

(2) A maximum square footage requirement for either an attached or detached accessory dwelling unit that is less than either of the following:

(A) Eight hundred fifty square feet of interior livable space.

(B) One thousand square feet of interior livable space for an accessory dwelling unit that provides more than one bedroom.

(3) Any requirement for a zoning clearance or separate zoning review or any other minimum or maximum size for an accessory dwelling unit, size based upon a percentage of the proposed or existing primary dwelling, or limits on lot coverage, floor area ratio, open space, front setbacks, and minimum lot size, for either attached or detached dwellings that does not permit an accessory dwelling unit with at least 800 square feet of interior livable space and with four-foot side and rear yard setbacks to be constructed in compliance with all other local development standards.

(4) Any height limitation that does not allow at least the following, as applicable:

(A) A height of 16 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit.

(B) A height of 18 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit that is within one-half of one mile walking distance of a major transit stop or a high-quality transit corridor, as those terms are defined in Section 21155 of the Public Resources Code. A local agency shall also allow an additional two feet in height to accommodate a roof pitch on the accessory dwelling unit that is aligned with the roof pitch of the primary dwelling unit.

(C) A height of 18 feet for a detached accessory dwelling unit on a lot with an existing or proposed multifamily, multistory dwelling.

(D) A height of 25 feet or the height limitation in the local zoning ordinance that applies to the primary dwelling, whichever is lower, for an accessory dwelling unit that is attached to a primary dwelling. This subparagraph shall not require a local agency to allow an accessory dwelling unit to exceed two stories.