Government Code § 66323(a)(3) requires cities to ministerially approve accessory dwelling units inside existing multifamily buildings, in portions not used as living space — storage rooms, boiler rooms, passageways, attics, basements and garages. At least one per building, and up to 25% of the existing unit count. Combined with § 66311.7, a pre-2020 unpermitted basement unit in an apartment building is squarely covered.

The by-right pathway in § 66323(a)(3) is written for space that wasn't living space. But § 66311.7(a)(2) separately bars a city from denying a permit for a pre-2020 unpermitted unit on the grounds that it "does not comply with this article" — which includes those standards. The unit still has to meet the definition of an accessory dwelling unit, and the only ground for denial is a substandard-building finding. We have taken units through this that we did not expect to qualify.

SB 543 (Stats. 2025, ch. 520) moved it. The text is substantively unchanged. Most published material still cites the old section.

Section 66311.7(e) prohibits impact fees and connection or capacity charges on a previously unpermitted unit built before January 1, 2020. The single narrow exception is where utility infrastructure must be upgraded to meet health and safety standards.

Sprinklers are not required in an accessory dwelling unit if they are not required in the primary residence, and creating the unit does not trigger a sprinkler requirement in the existing building.

Section 66329 preserves the Coastal Act but speeds the process: a decision within 60 days, no public hearing required, and processed alongside the ADU permit. In Redondo Beach, Manhattan Beach and Long Beach the city issues it. In Hermosa Beach west of Ardmore, and the thin coastal strip of Torrance, the Coastal Commission does.

Proposition 13 protects the base year value of the existing units. Only the new portion is assessed. There may also be an exclusion available for units completed before 2030, but that is a question for your tax advisor and we won't tell you it applies until they confirm it. Whether you notify the Assessor proactively is your call to make with your own advisor — we don't do it for you.

A city may deny only if it finds that correcting the violation is necessary to meet the substandard-building threshold in Health & Safety Code § 17920.3. Where work is genuinely required, the city must approve the permits to do it, and cannot penalize you.