SB 9 and ADU law in short
| Question | SB 9 (Gov. Code 65852.21, 66411.7) | State ADU law (Gov. Code 66310 to 66342) |
|---|---|---|
| What it allows | Two primary units on a single-family lot, a split into two lots, or both | Accessory units on lots with a house or multifamily building |
| Where | Single-family zones in urbanized areas | Any zone that allows single-family or multifamily homes |
| Minimum size the city must allow | Units of at least 800 sq ft; lots of at least 1,200 sq ft | An 800 sq ft ADU with 4-foot side and rear setbacks |
| Approval | Ministerial, approve or deny within 60 days | Ministerial; complete or incomplete within 15 business days, approve or deny within 60 days |
| Owner occupancy | 3-year residence affidavit for a lot split | None for ADUs; required for a JADU that shares a bathroom |
| Short-term rentals | Rentals must be longer than 30 days | Rentals of state-mandated ADUs and JADUs must be longer than 30 days |
The two laws are designed to work together, HCD's ADU Handbook says. A lot that uses SB 9 without splitting can have two primary units plus the ADUs and JADUs ADU law allows; a lot created by an SB 9 split is limited to two units of any kind.
A naming note: SB 9 here is the 2021 law (Chapter 162, Statutes of 2021). A different 2025 bill, also numbered SB 9 (Chapter 510, Statutes of 2025), amended ADU law. When you read a city notice, check the year.
SB 9 rules for duplexes and lot splits
SB 9 two-unit developments
On a qualifying lot in a single-family zone in an urbanized area, the city must approve up to two primary units ministerially, without a hearing. A city may deny only if the project would have a specific adverse impact on public health and safety or the physical environment that cannot be mitigated. Los Angeles City Planning's examples include two houses plus a detached ADU, a duplex plus two detached ADUs, and two houses plus a JADU.
SB 9 urban lot splits
An urban lot split divides one lot into two of roughly equal size. Los Angeles City Planning states the limits: neither new lot may be smaller than 40% of the original lot, both must be at least 1,200 square feet, and each may have no more than two units of any kind, counting ADUs and JADUs. A lot already created by an SB 9 split cannot be split again, nor can an adjacent lot split by the same owner or someone acting with them.
Local standards a city can and cannot apply
Cities may apply objective zoning, subdivision and design standards, but only if they apply uniformly in the zone, and they cannot be used to block one or two units of at least 800 square feet each or two lots of 1,200 square feet. Cities may require easements for utilities and access to a public right-of-way, but not dedications of right-of-way, off-site improvements or correction of nonconforming zoning conditions.
SB 9 parking and setbacks
A city may require up to one off-street parking space per unit, but none within one-half mile walking distance of a high-quality transit corridor or major transit stop, or within a block of a car-share vehicle. Side and rear setbacks may be no more than four feet, except that an existing structure with a smaller setback can stay as it is. Front setbacks follow the zone.
SB 9 owner affidavit and rental terms
An owner applying for a lot split must sign an affidavit that they intend to live in one of the units as their principal residence for at least three years from approval, unless the applicant is a community land trust or nonprofit. Rentals created under SB 9 must be for more than 30 days.
Where SB 9 does not apply
SB 9 is not available if the project would demolish or alter housing that is rent-restricted for moderate, low or very low income households, is under rent or price control, or was occupied by a tenant in the last three years. It also does not apply on a parcel where units were withdrawn under the Ellis Act in the last 15 years, to historic resources and contributing structures in historic districts, or on listed sensitive or hazardous lands such as wetlands and prime farmland.
SB 9 amendments in 2024 and 2025
SB 450 (Atkins, 2024) limited the design and zoning standards cities can impose on SB 9 projects. AB 1061 (Quirk-Silva, 2025) clarified the historic district exclusions. HCD has issued letters to Riverside, Fort Bragg, Laguna Beach, Long Beach and Menlo Park on SB 9 compliance; Laguna Beach, for example, was told it could not impose an owner-occupancy rule on SB 9 developments.
California ADU and JADU rules
The four types of state-mandated ADUs (Gov. Code 66323)
On a single-family lot, the city must allow one ADU converted from the house or an accessory structure, one JADU, and one new detached ADU of up to 800 square feet with four-foot side and rear setbacks, all together. On a multifamily lot it must allow ADUs in non-livable space such as storage rooms or garages (at least one, up to 25% of existing units) and up to two detached ADUs, or up to eight detached ADUs on a lot with an existing multifamily building, not more than the number of existing units.
ADU size limits
Under a compliant local ordinance, the maximum size must allow at least 850 square feet of interior livable space, or 1,000 square feet for an ADU with more than one bedroom. Where the city has no compliant ordinance, a new detached ADU can be up to 1,200 square feet and an attached ADU up to 50% of the house's floor area, with at least 800 square feet allowed. Front setbacks cannot block an 800 square foot ADU.
ADU height limits
A city cannot set a limit below 16 feet for a detached ADU; 18 feet within a half-mile walk of a major transit stop or high-quality transit corridor, plus 2 feet to match the roof pitch of the house; and 18 feet on a lot with a multistory multifamily building. An attached ADU can be 25 feet or the zone's height limit for the house, whichever is lower. If a two-story ADU fits within those heights, the city cannot deny it because the zone limits houses to one story.
ADU setbacks and parking
Side and rear setbacks for an ADU can be no more than four feet, and none are required when converting existing space or rebuilding a structure in the same footprint. Parking can be no more than one space per unit or bedroom, whichever is less, and none can be required within a half-mile walk of public transit, in a historic district, for a converted ADU, or when a car share is within a block. Garage parking lost to an ADU does not have to be replaced.
Permit timelines
Under the 2025 amendments, the permitting agency must tell you within 15 business days whether an application is complete, with a list of missing items if not, and must approve or deny a complete application within 60 days. A denial must come with written comments explaining how to fix the application, and there must be an appeal process with a final decision within 60 business days. Cities had to set up pre-approved ADU plan programs by January 1, 2025.
Impact fees and utility charges
No impact fees may be charged on an ADU of 750 square feet of interior livable space or less, or a JADU of 500 square feet or less. Above that, fees must be proportional to the ADU's size compared with the main house. School districts may charge fees only on units over 500 square feet. Converted ADUs and JADUs are not a new residential use for water and sewer connection fees unless built with a new house.
Owner occupancy and deed restrictions
A city cannot require the owner to live on the property for an ADU, and cannot impose an affordability deed restriction on it. A JADU that shares a bathroom with the house requires the owner to live on site, and a city's JADU ordinance must require a recorded deed restriction barring separate sale of a JADU.
Junior ADUs
A JADU is up to 500 square feet of interior livable space inside a single-family house, including an attached garage. Without its own bathroom it needs a separate entrance plus an interior door to the main home. Since January 1, 2026 a JADU cannot be a short-term rental.
ADUs in HOA communities
Civil Code 4751 and 714.3 void CC&Rs that effectively prohibit or unreasonably restrict an ADU or JADU on a lot zoned for single-family use, and a reasonable restriction cannot include fees. Architectural review still applies; see the California HOA laws guide.
Selling an ADU separately
An ADU normally cannot be sold apart from the main house. Since 2024 a city may adopt an ordinance allowing the house and ADU to be sold as condominiums (Gov. Code 66342), and a narrow exception allows sale to a qualified low or moderate income buyer when a qualified nonprofit built the units (Gov. Code 66341).
Legalizing an existing unpermitted ADU
A city cannot deny a permit for an unpermitted ADU built before January 1, 2020 just because it breaks building standards or ADU rules, unless correcting the violation is needed for health and safety or the building is substandard. Cities must publish a checklist of substandard conditions and tell owners they may get a confidential inspection from a licensed contractor first.
Worked examples: SB 9 and ADU numbers
Example 1: an SB 9 lot split
A 6,000 square foot single-family lot is split 60/40. The new lots are 3,600 and 2,400 square feet. The smaller lot is exactly 40% of the original (2,400 / 6,000), and both are above 1,200 square feet, so the split meets both tests. Each lot can have two units, so the original lot can end up with four homes. A 70/30 split (4,200 and 1,800 square feet) fails the 40% test even though both lots are over 1,200 square feet.
Example 2: SB 9 without a split
The same 6,000 square foot lot is not split. The owner builds two primary units under SB 9 and adds an ADU and a JADU under ADU law, which HCD's fact sheet gives as an allowed combination: four units on one lot with no subdivision.
Example 3: impact fees
A 750 square foot detached ADU pays no impact fees. HCD's handbook gives the proportional rule for larger units: a 1,000 square foot ADU behind a 2,000 square foot house could be charged 50% of the impact fee for a new house on the same site. If the city's fee for a new house were $20,000, the ADU would pay up to $10,000, so trimming the design to 750 square feet could save that whole amount.
Example 4: property tax on a new ADU
Under Prop 13, completed new construction is assessed at market value when finished and added through a supplemental bill (BOE Publication 29). If the assessor values a finished ADU at $300,000, the 1% base rate adds about $3,000 a year before voter-approved local rates. Ask your county assessor how it will value your project before you build; the California property tax guide explains the supplemental bill.
ADU numbers and financing
How many ADUs California permits
HCD reports that ADU permits grew from 1,336 in 2016 to 30,354 in 2024, a 20-fold increase, and that ADUs made up more than 26.6% of all homes permitted statewide in 2024.
Loans that count ADU rent
HCD's handbook notes that FHA, Fannie Mae and Freddie Mac now offer financing for homes with ADUs, including counting ADU rental income toward qualifying in some programs; FHA's 203(k) renovation loan can be used only for an attached ADU. The CalHFA ADU Grant, which reimbursed up to $40,000 of predevelopment costs, had exhausted its funds when the handbook was written. Ask your city whether it waives fees or runs its own ADU program.
Buying a home with an ADU or SB 9 potential
Before you buy, ask the seller for permits and the certificate of occupancy for any existing ADU, check the zoning and whether the lot sits in a historic district or on other land SB 9 excludes, and confirm with the planning counter what your city allows. Our home buying guide covers the contingency period for that research.
Common SB 9 and ADU mistakes
- Confusing the two SB 9 bills. The 2021 law covers duplexes and lot splits; a 2025 bill with the same number amended ADU law.
- Splitting a lot you do not plan to live on. An SB 9 lot split requires a three-year owner residence affidavit.
- Using SB 9 where a tenant lived recently. It does not apply if the work would alter or demolish housing occupied by a tenant in the last three years.
- Designing just over 750 square feet. Impact fees start above that size.
- Planning a short-term rental. SB 9 units and state-mandated ADUs and JADUs must be rented for more than 30 days.
- Assuming an HOA can say no. CC&Rs cannot prohibit or unreasonably restrict an ADU on a single-family lot, though design review still applies.
- Relying on an old city handout. ADU sections were renumbered in 2024 and changed again on January 1, 2026; check HCD's current handbook.