California ADU laws let most homeowners add an accessory dwelling unit through a permit that cannot require a hearing or discretionary review. State law sets the floor for size, height, setbacks, parking, and fees. Your city can be more generous than that floor, but not stricter. Two more changes arrive on January 1, 2027: a second detached ADU on single-family lots (AB 956) and a new way of calculating impact fees on larger units (SB 1117).
This guide reflects the law as of October 11, 2026, based mainly on the HCD ADU Handbook (March 2026). It is not legal advice.
California ADU laws at a glance
| Topic | What your city must allow |
|---|---|
| Approval | Ministerial review, no hearing. Completeness decision in 15 business days, then approval or denial within 60 days |
| Size | New detached ADU: 800 sq ft protected by state law. City ordinances must allow at least 850 sq ft (1,000 for 2+ bedrooms). JADU: 500 sq ft maximum |
| Height | Detached: 16 ft, or 18 ft (plus 2 ft for roof pitch) near transit. Attached: 25 ft or the main home’s limit if lower |
| Setbacks | No more than 4 ft at side and rear. None for conversions |
| Impact fees | None at 750 sq ft or less (JADU: 500 or less). Proportional above that |
| Owner on site | Not required for ADUs. Required for a JADU only if it shares a bathroom with the main home |
| Rentals | California Cities may require terms longer than 30 days |
What changed between 2025 and 2027
| Law | Effect | Effective |
|---|---|---|
| AB 2533 | Legalization path for unpermitted ADUs built before 2020 | Jan. 1, 2025 |
| SB 1211 | Up to eight detached ADUs on an existing multifamily lot, capped at the number of existing units | Jan. 1, 2025 |
| SB 543 | Size measured by interior livable space; 15-business-day completeness check; appeals | Jan. 1, 2026 |
| AB 1154 | JADU owner-occupancy only when the bathroom is shared; no short-term JADU rentals | Jan. 1, 2026 |
| AB 956 | Two detached new-construction ADUs per single-family lot, up from one | Jan. 1, 2027 |
| SB 1117 | Fees on the first two ADUs charged only on area above 750 sq ft | Jan. 1, 2027 |
The 2027 rows come from a law firm summary of bills signed in late September 2026; cities had not yet published guidance.
How California ADU laws work: state minimums and local rules
A city ordinance can add objective standards such as materials, but nothing stricter than state law. If there is no ordinance, or it is void, state standards apply directly.
The key distinction is Government Code section 66323. Conversions, one new detached ADU, and multifamily ADUs fall under it, and cities cannot apply their own parking, lot-size, open-space or design standards to them. Everything else, such as an attached addition, follows the city ordinance. Building and fire codes still apply. Check your lot with the Zoning Information Lookup.
How many ADUs can you build on your lot?
Single-family lots. Cities must allow one conversion ADU, one JADU and one new detached ADU, plus at least one ADU under the city’s own ordinance. That is a legal ceiling, not a promise for your lot. From January 1, 2027, AB 956 allows two new detached units instead of one; ask your city how it will size the second. A JADU must sit inside the main home (an attached garage counts), one per lot.
Multifamily lots. Cities must allow conversions of non-livable space (storage rooms, garages) up to 25 percent of existing units, plus up to eight detached ADUs capped at the number of existing units (two for a proposed building). See multifamily ADU laws.
SB 9 (2021). It works alongside ADU law: after a lot split each parcel gets at most two units, and past four units on a lot a city need not approve a split. See our SB 9 guide.
Size, height, setbacks and parking by ADU type
| ADU type | Size | Height | Setbacks |
|---|---|---|---|
| JADU | 500 sq ft, inside the main home | Existing | None beyond fire and safety |
| Conversion | No cap; an accessory structure can add 150 sq ft for stairs or entry | Existing | None |
| New detached, state-protected | 800 sq ft | 16 ft; 18 ft near transit | 4 ft side and rear; front setback cannot block it |
| Under city ordinance | At least 850 (1,000 for 2+ bedrooms). No ordinance: 1,200 detached, or 50% of the main home attached (never under 800) | 16 ft; 18 ft near transit; 25 ft attached | 4 ft side and rear at most |
Size counts interior livable space. No minimum lot size applies, and lot coverage or open-space rules cannot block an 800 sq ft ADU with 4 ft setbacks. Extra transit height applies within a half mile of a major transit stop; see our setback guide.
Parking. At most one space per unit or bedroom, whichever is less, and none within a half-mile walk of public transit, in a historic district, inside the main home or an accessory structure, within one block of car share, or when built with a new home. Replacement parking for a converted garage is not required. See ADU parking requirements.
Impact fees and the 750 sq ft line
An ADU of 750 square feet or less cannot be charged impact fees (JADU: 500). A 750 sq ft unit qualifies, so designing to 749 is unnecessary. Above 750, fees must be proportional to the main home’s size. HCD’s example: a 1,000 sq ft ADU behind a 2,000 sq ft house could owe 50 percent of a new house’s fee, not the full schedule.
SB 1117 (2027). Some cities charged the per-foot rate on the whole unit once it passed 750. From 2027, fees on the first two ADUs are to be based only on the area above 750. With a made-up $10 per square foot, a 900 sq ft ADU would owe $9,000 on its full area but $1,500 on the 150 above the line. Get your city’s real schedule before choosing a size.
Not impact fees. Utility connection and capacity charges follow separate rules: none for a conversion, proportional for other ADUs. School districts can still charge on ADUs over 500 sq ft, per HCD. See our utility hookup laws.
Permit timelines: the 15-day and 60-day clocks
- 15 business days for the agency to say in writing whether your application is complete. Miss it, and the application is deemed complete. An incomplete notice must list what is missing.
- 60 days from a complete application to approve or deny. Under Government Code 66317, no decision in 60 days means deemed approved. Delays you request pause the clock.
- A full set of comments if denied.
- 60 business days for a written decision on an appeal.
The 60 days bind every permitting agency, including utilities, but not design or construction. A certificate of occupancy is needed before anyone moves in.
If your city is slow. Ask about pre-approved plans. AB 253, signed October 10, 2025, lets applicants on small residential projects hire a private plan checker when the city estimates over 30 business days (summary); confirm it covers your ADU. You can report suspected violations to HCD. See our permit checklist.
Living on site, renting and selling
Owner-occupancy. Cities cannot require you to live on the property for a standard ADU; AB 976 made that permanent in 2024. A JADU needs an owner on site only if it shares a bathroom with the main home.
Rentals. Cities can require ADU rentals longer than 30 days; for state-protected ADUs and JADUs that floor is state law, and JADUs cannot be short-term rentals. Some online guides say otherwise.
Condo sales. AB 1033 does not give you the right to sell. It lets a city adopt an ordinance under Government Code section 66342 allowing separate condominium sales. San Diego County adopted one on March 4, 2026, and San José publishes a conversion checklist, but a July 2026 review found Los Angeles had not. Ask your city first.
Legalizing an unpermitted ADU
Under AB 2533 (Government Code section 66311.7), a city cannot deny a permit to legalize a unit built before 2020 for building-standard or local-rule violations. It can deny if correction is necessary for health and safety or the building is substandard under Health and Safety Code section 17920.3. Applicants generally owe no impact or connection charges unless utility work is needed for safety. Owners can also request up to five years’ delay of enforcement on non-safety violations; local programs note it cannot postpone safety fixes. See our amnesty guide.
Budget and costs the law affects
State law sets no construction prices, but it limits impact fees, connection charges for conversions and replacement parking. Sprinklers are required only if the main home needs them, and new detached ADUs generally must meet the Energy Code solar requirement (Title 24 guide).
The Terner Center’s 2021 survey found a median statewide construction cost of $150,000, about $250 per square foot, and a median rent of $2,000. That is historical, not a quote. For current ranges, see what an ADU costs in California, then use the ADU Cost Calculator, ADU Budget Worksheet and ADU Loan Calculator.
Questions to ask your city before paying for design
- Does the city have an ADU ordinance, and was it sent to HCD?
- What is the impact fee schedule per square foot, and does the school district charge?
- Are there pre-approved plans, and how fast are they reviewed?
- Is a separate utility connection required?
- Has the city adopted AB 1033, and how will it apply AB 956 and SB 1117?
If a planner cites a minimum lot size or owner-occupancy rule for a standard ADU, ask for the code section in writing; it conflicts with state law. Check any builder with the Contractor License Lookup. City guides: Los Angeles, San Diego, San Jose.
Frequently asked questions
Can my HOA stop me from building an ADU?
No. Covenants that effectively prohibit or unreasonably restrict an ADU on a single-family lot are void. See HOA rules vs ADU laws.
Can I build in the coastal zone?
Yes. A city with a certified coastal program must decide an ADU’s coastal permit within 60 days of a complete application.
Next steps
Match your lot to the tables above, then take the questions list to your planning department. The AI ADU Design Advisor can help narrow the type, and our contractor directory lists builders near you.
