State Law | ADUs and JADUs
California ADU Law 2026: How Many ADUs Your Lot Can Have
An accessory dwelling unit (ADU) is a second, smaller home on a lot that keeps its main house or apartment building. A junior ADU (JADU) is a unit of 500 square feet or less built inside the walls of the house. California ADU law makes cities approve both through ministerial review, meaning staff check the plans against fixed written rules, with no hearing. This page covers what the law allows in 2026, what changes on January 1, 2027, and the fee, size and parking rules that decide your budget.
California ADU law in six facts
- On a single-family lot, a California city must approve one ADU and one junior ADU inside the house or an existing accessory building, plus one new detached ADU it may cap at 800 square feet. Source: Gov. Code 66323
- From January 1, 2027, AB 956 raises the detached ADUs a city must approve on a single-family lot from one to two. Source: AB 956 (2026)
- A city's maximum ADU size cannot be set below 850 square feet, or 1,000 square feet for an ADU with more than one bedroom. Source: Gov. Code 66321
- An ADU of 750 square feet or less, or a junior ADU of 500 square feet or less, pays no impact fees. Source: HCD ADU Handbook
- The city has 15 business days to say if an ADU application is complete, and 60 days to approve or deny it when a home already stands on the lot. Source: Gov. Code 66317
- On a lot with an existing multifamily building, a city must allow up to eight detached ADUs, but no more than the number of existing units. Source: Gov. Code 66323
Where the Law Lives
State ADU law is in Government Code sections 66310 to 66342. It used to sit in sections 65852.2, 65852.22, 65852.23 and 65852.26. SB 477 (Chapter 7, Statutes of 2024) moved it, and the new sections show an effective date of March 25, 2024 in the code history. If an older guide cites 65852.2, it is the same law under its old number.
The main state guide is the ADU Handbook from the California Department of Housing and Community Development (HCD). Its current edition is dated March 2026 and reflects the law in effect on January 1, 2026. It does not yet cover the two ADU bills signed on September 29, 2026, AB 956 and SB 1117, which start on January 1, 2027.
One naming warning. SB 9 (2021) is the lot split law. A different bill, SB 9 of 2025 (Chapter 510, Statutes of 2025), is an ADU bill: HCD explains that a city ADU ordinance not sent to HCD within 60 days, or not fixed after HCD finds problems, is "null and void," and the city must then apply state ADU law alone.
What a City Must Approve, by Lot Type
| Lot | Inside existing space | New detached ADUs | Homes |
|---|---|---|---|
| Single-family lot, today | 1 ADU converted from existing space (with up to 150 sq ft added for entry) and 1 junior ADU | 1 new detached ADU, 4-foot side and rear setbacks, city may cap at 800 sq ft | House plus 3 |
| Single-family lot, from January 1, 2027 (AB 956) | 1 converted ADU; a junior ADU is not required where 2 new detached ADUs are built | 2 new detached ADUs, each subject to the 800 sq ft cap and height rules | House plus 3 |
| Lot with an existing multifamily building | At least 1, and up to 25% of the existing unit count, in non-livable space such as storage rooms, attics, basements and garages | Up to 8, but no more than the number of existing units | Depends on unit count |
| Lot with a proposed multifamily building | Not covered by this rule | Up to 2 | New building plus 2 |
Sources: Gov. Code 66323, AB 956 and the HCD ADU Handbook.
Single-Family Lots Today
Government Code 66323(a) lists the ADUs a city must approve by staff review "in any combination." On a single-family lot that means one ADU and one junior ADU inside the existing or proposed house or an existing accessory building such as a garage, with up to 150 square feet of expansion for entry and exit, plus one new detached ADU with four-foot side and rear setbacks. The city may cap that detached unit at 800 square feet of livable space. HCD says it plainly: "on single-family lots, local agencies must allow at least one ADU constructed from existing space, one JADU, and one newly constructed detached ADU."
That makes four homes on one lot under ADU law alone: the house, the converted ADU, the junior ADU and the detached ADU. The ADUs in this section need no parking at all, and they must be rented, if rented, for terms longer than 30 days.
Starting January 1, 2027: AB 956
AB 956 (Chapter 791, Statutes of 2026) was chaptered on September 29, 2026 and takes effect January 1, 2027. It rewrites 66323(a)(2) to read "Two detached, new construction, accessory dwelling units" on a lot with a proposed or existing single-family home. Each stays subject to the 800 square foot cap and height rules the city may apply. The bill also says a city does not have to approve a junior ADU on a lot where two new detached ADUs have been built.
AB 956 makes one more change. The rule that voids homeowners association (HOA) and deed restrictions on ADUs will reach any lot "zoned to allow single-family residential use." If an HOA has blocked your backyard unit, read the new rule with an attorney before you apply in 2027.
Multifamily Lots, Including Duplexes
SB 1211 (Chapter 296, Statutes of 2024) wrote the current rule for lots with apartment buildings. On a lot with an existing multifamily building, the city must allow up to eight detached ADUs, but no more than the number of existing units. On a lot with a proposed multifamily building, it must allow up to two detached ADUs. Inside the existing building, owners can convert non-livable space such as storage rooms, boiler rooms, attics, basements and garages into at least one ADU, and up to 25 percent of the existing unit count.
HCD's handbook defines what counts as multifamily: "a structure with two or more attached dwellings on a single lot is considered a multifamily dwelling structure." So an existing duplex qualifies for these rules, and can add up to two detached ADUs. Several detached houses on one lot do not count as multifamily. The duplex to fourplex page works through those combinations.
Size, Height and Parking Limits
| Rule | State limit |
|---|---|
| Lowest maximum size a city may set | 850 sq ft; 1,000 sq ft with more than one bedroom |
| State default size, detached ADU | 1,200 sq ft, where no compliant city ordinance exists |
| State default size, attached ADU | 50% of the existing home |
| Size that lot coverage, floor area ratio and front setback rules cannot block | 800 sq ft with 4-foot side and rear setbacks |
| Height a city must allow, detached ADU | 16 ft |
| Height near a major transit stop or high-quality transit corridor | 18 ft, plus 2 ft to match the roof pitch of the main home |
| Height on a lot with a multistory multifamily building | 18 ft |
| Height, attached ADU | 25 ft or the zone height limit, whichever is lower; no more than 2 stories required |
| Junior ADU size | 500 sq ft or less, inside the walls of the house |
| Parking a city may require | 1 space per ADU or per bedroom, whichever is less, with many exemptions |
Sources: Gov. Code 66321, 66314, 66322 and 66333.
A city's own size limit cannot drop below 850 square feet of interior livable space, or 1,000 square feet for an ADU with more than one bedroom, under Government Code 66321. Lot coverage, floor area ratio (the building's floor area divided by the lot area), open space, front setback and minimum lot size rules cannot be used to block an 800 square foot ADU with four-foot side and rear setbacks.
Parking is limited to one space per ADU or per bedroom, whichever is less. No parking may be required for an ADU within one-half mile walking distance of public transit, in an architecturally and historically significant historic district, inside the existing house or accessory building, where on-street permits are required but not offered to the ADU, or within one block of a car share vehicle. When a garage or carport is converted or torn down for an ADU, the city cannot require replacement parking.
Deadlines and Appeals
SB 543 (Chapter 520, Statutes of 2025), in effect since January 1, 2026, added the completeness deadline and the appeal rules. Under Government Code 66317, the permitting agency has 15 business days to say whether an ADU or junior ADU application is complete, or it is deemed complete. It must approve or deny a complete application within 60 days when a single-family or multifamily home already stands on the lot. You can appeal a finding of incompleteness or a denial, and the agency must decide the appeal within 60 business days.
Pre-approved plans are another option. Under AB 1332, every city had to set up a program to preapprove ADU plans by January 1, 2025, and post the approved plans online. Los Angeles runs one through its ADU Standard Plan Program.
Owner Occupancy, Junior ADUs and Rentals
A city cannot require the owner to live on a lot with an ADU, under Government Code 66315. Junior ADUs follow different rules. There can be only one per single-family lot. It must be inside the walls of the house, and an attached garage counts. It needs a recorded deed restriction against separate sale. Since January 1, 2026, under AB 1154 (Chapter 507, Statutes of 2025), the owner must live on site only when the junior ADU shares a bathroom with the main house.
A city may require ADU rentals to last longer than 30 days, and must require it for the ADUs listed in 66323 and for every junior ADU. Apart from the junior ADU rules, HCD says a city "cannot impose a deed restriction on an ADU," including an affordability covenant.
Impact Fees and the 750 Square Foot Rule
Impact fees are one-time charges a city, special district or water company collects to pay for public facilities. Under Government Code 66311.5, an ADU of 750 square feet of interior livable space or less pays none, and neither does a junior ADU of 500 square feet or less. Above 750 square feet, fees must be proportional to the size of the main home. HCD's example: "a 2,000 square-foot primary dwelling with a proposed 1,000 square-foot ADU could result in 50 percent of the impact fee."
School districts may charge their fees only on ADUs over 500 square feet. Utilities cannot treat a converted ADU or junior ADU as a new use for connection fees, unless it is built with a new house. Starting January 1, 2027, SB 1117 (Chapter 809, Statutes of 2026) changes the rule for lots with up to two ADUs: fees on an ADU above 750 square feet apply "only on the area in excess of 750 square feet." Lots with more than two ADUs keep the current proportional rule. The impact fees page covers school fees and the other charges on a new home.
Selling an ADU, Old ADUs and Other Rules
Separate sale. AB 1033 (Chapter 752, Statutes of 2023), in effect since January 1, 2024, lets a city adopt an ordinance allowing the main home and its ADUs to be sold separately as condominiums. It is a local choice. Under Government Code 66342, the owner needs a safety inspection before the condominium plan is recorded and the written consent of every lienholder (each lender with a loan on the property), and "a lienholder may refuse to give consent." Inside an existing HOA, the board must also approve in writing. San Jose and San Diego have opted in; see their city pages.
Unpermitted ADUs. Under AB 2533 (Chapter 834, Statutes of 2024), in effect since January 1, 2025, a city cannot deny a permit for an unpermitted ADU or junior ADU built before January 1, 2020 only because it breaks building or ADU rules, unless the fix is needed to meet the health and safety standards of Health and Safety Code 17920.3. Cities must post a checklist and tell owners they can get a confidential inspection from a licensed contractor first.
Fire sprinklers. A city cannot require sprinklers in an ADU or junior ADU unless the main home needs them, and an ADU cannot trigger sprinklers in the main home. Charter cities. HCD says ADU law applies to every city and county "whether general law or chartered." Solar. A new detached ADU must meet the Energy Code solar rule, with some exceptions, and the panels can sit on the ADU or the house. See the energy code page.
How Many ADUs California Builds
The Department of Finance counted 29,710 ADUs added to the state's housing in 2025, an 11.42 percent increase over 2024. In the same release, ADUs made up 15.2 percent of all new housing built in 2025.
Permits show the trend. In their annual progress reports to HCD, California cities and counties reported 9,005 ADU building permits in 2018 and 41,846 in 2025. Certificates of occupancy, issued when a home is finished, rose from 18,536 in 2023 to 24,334 in 2025. These totals are VanPlex's own sum of HCD's published Table A2 data. Permits and finished homes measure different stages, so the two counts do not match.
ADUs and Your Mortgage
Lenders count ADUs by their own rules. Fannie Mae allows only one ADU on a one-unit property, does not recognize ADUs on two- to four-unit properties, and caps qualifying ADU rent at 30 percent of total qualifying income. Freddie Mac's February 2026 fact sheet allows one ADU on one-, two- and three-unit properties and bars using rent from an illegal ADU to qualify. HCD notes that FHA's 203(k) rehabilitation loan "may only be used to construct an attached ADU." The financing page has the details.
Best For
- ✓ Owners who want to keep one lot and add rental homes with staff approval.
- ✓ Lots that fail SB 9 because of zone, tenant history or a past split.
- ✓ Existing duplexes and apartment buildings with storage, attic or garage space to convert.
Usually Fails When
- ✕ The design goes over 750 square feet without a budget for impact fees.
- ✕ The owner wants to sell the ADU in a city that has not opted in to AB 1033.
- ✕ A junior ADU shares a bathroom and the owner does not plan to live on site.
What To Verify Before Spending Money
- → Your city's ADU ordinance and whether HCD has accepted it.
- → Whether the lot is within one-half mile walking distance of transit, for parking and height.
- → Whether a 2027 filing under AB 956 and SB 1117 would suit the project better.
Where to Go Next
For comparison with Canada, see VanPlex's laneway and ADU guide for British Columbia.
Frequently Asked Questions
How many ADUs can I build on a single-family lot in California?
How big can an ADU be in California?
Do I have to live on the property to build an ADU in California?
Can I sell my ADU separately from the house in California?
Do ADUs pay impact fees in California?
How long does a California city have to approve an ADU permit?
Do I need parking for an ADU in California?
Can I legalize an unpermitted ADU in California?
How many ADUs can I add to a duplex or apartment building?
Can my HOA stop me from building an ADU in California?
How tall can an ADU be in California?
Does a new ADU in California need solar panels?
Official sources (checked October 2026)
Planning a multiplex in California?
VanPlex builds multiplexes and models lots in British Columbia, Canada. We do not build, lend, or broker in California yet. Join the California list and we will tell you when that changes.