California has passed more ADU legislation in the past six years than most states pass in a generation. The result is a statewide floor that strips away most of the barriers local governments used to block accessory dwelling units — but the floor is not a ceiling, and municipalities still control enough variables that you need to read the local code before you count on a project penciling out.

The Core Laws and What Each One Did

Four bills form the backbone of California's ADU reform. Understanding what each one actually changed — rather than treating them as one undifferentiated wave of reform — matters because different provisions interact with different projects.

AB 68 (2020): The Foundation

AB 68 was the first major statewide reset. It eliminated minimum lot size requirements for ADUs, prohibited local rules requiring a garage replacement if an ADU converts an existing garage, and capped permit approval timelines at 60 days. It also banned local governments from requiring owner-occupancy as a condition of ADU approval — a requirement that had been used to chill investor activity in many jurisdictions. AB 68 established that ADUs are a ministerial, by-right approval: if your project meets the objective standards, the city has to issue the permit.

SB 9 (2022): Lot Splits and Duplexes

SB 9 did not specifically target ADUs but dramatically expanded what you can build in single-family zones. It requires cities to ministerially approve a lot split on most single-family parcels and to allow a duplex on each resulting lot. Combined with ADU rights, a single-family parcel that qualifies for a lot split could theoretically support four units total. SB 9 applies to most urban and suburban areas and does not require a variance or hearing — it is by right. Local design review for objective standards still applies.

AB 2221 (2023): Size and Height Clarifications

AB 2221 addressed an ongoing dispute between the state and local governments over how to measure ADU size limits. It clarified that cities cannot use floor area ratio rules to prohibit an ADU that would otherwise comply with the state minimums — at least 850 square feet for a studio or one-bedroom, 1,000 square feet for two or more bedrooms. It also set a minimum height of 16 feet for detached ADUs, which prevents cities from using height limits to effectively ban construction of a reasonably functional unit.

AB 976 (2024): Owner-Occupancy Eliminated Permanently

AB 976 closed a loophole. Earlier law prohibited owner-occupancy requirements but allowed existing local ordinances that predated the state law to remain in effect until 2025. AB 976 made the prohibition permanent and retroactive — no California municipality can require an owner to live on the property as a condition of building or renting an ADU. This matters for investors who purchase properties specifically to build and rent ADUs without intending to occupy them.

Junior ADUs: Different Rules Apply

A junior ADU (JADU) is a unit up to 500 square feet carved out of the existing living space of a single-family home — a converted bedroom, basement room, or attached garage. JADUs have their own set of rules that are more restrictive in some respects. Local governments can still require the owner to occupy either the primary home or the JADU (though not both), meaning the owner-occupancy prohibition that applies to standard ADUs does not apply to JADUs. The JADU must have an efficiency kitchen with a cooking facility and a food preparation counter, and it must have its own exterior door, though it can share a bathroom with the main house. For investors who intend to operate entirely as landlords without residing on site, a standard ADU rather than a JADU is usually the appropriate path.

What Municipalities Can Still Control

The state law sets minimums, not a uniform statewide standard. Local governments retain meaningful control over several variables that affect project feasibility.

  • Setbacks: Cities can require up to 4 feet of rear and side setbacks for new detached ADUs. Some cities require less. Existing structures converted to ADUs are generally exempt from setback requirements.
  • Design review: Objective design standards — things like roof pitch, exterior materials, and window placement — are still allowed. What cities cannot do is apply subjective architectural review that gives a reviewer discretion to reject a project for aesthetic reasons.
  • Parking near transit: Within half a mile of a transit stop, cities cannot require any parking for an ADU. Outside that buffer, they can require one parking space per ADU, though not more.
  • Height limits for multi-story ADUs: The 16-foot minimum protects single-story ADUs. For taller structures, local height limits apply, though cities near single-family zones in specific contexts must allow up to 25 feet.
  • Short-term rental restrictions: The state ADU law does not require cities to allow ADUs to be used as short-term rentals. Many California cities prohibit or limit Airbnb-style rentals in ADUs. If your investment thesis depends on vacation rental income, check the local STR ordinance separately.

The Practical Research Checklist

Even with strong state preemption, you cannot skip local due diligence. Here is what to verify before committing to a California ADU project:

  1. Pull the local ADU ordinance — most cities post it on their planning department website or link to it from the permit portal.
  2. Confirm the setback requirements for the specific parcel, including whether an existing structure qualifies for the conversion exemption.
  3. Check whether the parcel is in a historic district, a very high fire hazard severity zone, or a coastal zone — all of which layer additional review requirements on top of standard ADU rights.
  4. Confirm utility connection fees. State law limits connection fees for ADUs under 750 square feet to zero in many circumstances, but larger units and new construction units have different rules.
  5. Check the short-term rental ordinance if rental income projections assume STR use.
  6. For JADUs, confirm whether the local ordinance requires owner-occupancy and whether that constraint affects your intended ownership structure.

Why State Law Isn't the Whole Story

California's ADU reforms have genuinely opened up the market. By-right approval, no owner-occupancy requirements for standard ADUs, and minimum size guarantees mean that a well-sited project on a standard lot is very likely approvable somewhere in the permitting process. But "approvable" is different from "financially viable." Impact fees, utility connection costs, construction costs in high-labor-cost markets, and local design standards can all compress margins. The state law tells you whether you can build; a full project underwrite tells you whether you should.

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