California ADU laws in 2026 give homeowners strong, enforceable rights to build. State law, now in Government Code sections 66310 to 66342, sets the maximum rules a city may apply: the city can be more generous, but not stricter. Here is what the law says, including the changes that took effect January 1, 2026.
What changed on January 1, 2026
| Law | What it changed |
|---|---|
| SB 543 | Cities must decide whether an ADU or JADU application is complete within 15 business days, or it is deemed complete. Size limits are measured as interior livable space, including the existing impact fee exemption for ADUs under 750 sq ft and JADUs. |
| AB 1154 | A JADU with its own bathroom has no owner-occupancy requirement; owner-occupancy can apply only when the JADU shares a bathroom with the main home. JADUs, and ADUs built under the state’s guaranteed rules (Gov. Code 66323), must be rented for terms longer than 30 days. |
Source: HCD ADU fact sheet, April 2026.
The core rules every California city must follow
| Rule | State law |
|---|---|
| Approval type | Ministerial. No public hearing; only objective standards (numbers, measurable rules), never “compatibility” or “design harmony.” |
| Decision deadline | 60 days after a complete application, or the ADU is deemed approved. A denial must list every deficiency and how to fix it. |
| Detached ADU size | Cities must allow at least 850 sq ft (1,000 sq ft with more than one bedroom). With no local ordinance, up to 1,200 sq ft. |
| Attached ADU size | Where the city has no ordinance, up to 50% of the main home’s floor area. Local limits cannot block an 800 sq ft ADU with 4 ft setbacks. |
| Junior ADU (JADU) | Up to 500 sq ft, inside the existing home or attached garage. One per single-family lot. Cannot be sold separately. |
| Height, detached | At least 16 ft; 18 ft near major transit or on a multistory multifamily lot (plus 2 ft to match the roof pitch near transit). |
| Height, attached | At least 25 ft, or the zone’s height limit if lower. |
| Side and rear setbacks | No more than 4 ft. None for a conversion of an existing structure. |
| Parking | At most 1 space per ADU. None required within half a mile of public transit, in a historic district, for conversions, and in other cases. A garage torn down for an ADU does not have to be replaced. |
| Owner-occupancy | Never required for an ADU (permanent since January 1, 2024). |
| Rentals | Longer than 30 days for JADUs and for ADUs built under Gov. Code 66323 (conversions, the guaranteed 800 sq ft detached unit, multifamily ADUs). Cities may require the same for other ADUs. |
| Fire sprinklers | Not required unless the main home requires them. Building an ADU cannot trigger sprinklers in the main home. |
| HOAs | CC&Rs cannot ban or unreasonably restrict ADUs on single-family lots (Civil Code 4751). |
Source: HCD Accessory Dwelling Unit Handbook and ADU portal.
How many units can you build?
On a single-family lot, state law guarantees you can build all three at once:
- one ADU converted from space inside your home or an existing accessory structure,
- one junior ADU, and
- one new detached ADU of up to 800 sq ft with 4 ft setbacks.
On a multifamily lot, you can convert non-living space (storage rooms, garages) into ADUs, at least one and up to 25% of the existing unit count, and build up to eight detached ADUs on a lot with existing apartments, but not more detached ADUs than existing units.
Fees: what a city can and can’t charge
- Impact fees: none on ADUs under 750 sq ft or on JADUs. Above 750 sq ft, fees must be proportional to the ADU’s size compared with the main home.
- School fees: school districts may charge on units over 500 sq ft.
- Utility connection fees: must be proportionate to the ADU’s burden on the system; a conversion or JADU generally can’t be charged a new connection fee.
Unpermitted ADUs built before 2020
If you own an ADU that was built without permits before January 1, 2020, the city cannot deny a permit to legalize it because of building code or zoning violations, unless a correction is needed to protect health and safety. That makes many older garage conversions eligible to be legalized.
Selling an ADU separately
Under AB 1033, a city may adopt an ordinance letting owners sell an ADU separately as a condominium. Unless your city has adopted such an ordinance, or a qualified nonprofit is involved, state law does not allow an ADU to be sold separately from the main home, so plan on it staying part of your property.
Prefab and factory-built ADUs
State law treats a factory-built or manufactured ADU like any other ADU: the same size, height, setback and parking rules apply. The factory’s plans are approved through HCD’s factory-built housing program; your city reviews the foundation, site work, utilities and installation. More in How a prefab ADU is delivered and installed.
Frequently asked questions
Can my city deny my ADU?
Only for failing objective standards in state law or a compliant local ordinance, and it must explain every deficiency in writing within 60 days. If the city doesn’t act in time, the application is deemed approved.
Does my HOA have to allow an ADU?
On a single-family lot, yes. The HOA can apply reasonable, objective design rules, but cannot ban ADUs or make them unreasonably expensive.
Do I have to live on the property?
Not for an ADU. For a junior ADU, only if it shares a bathroom with the main home.
Questions about your lot? Call (800) 806-7485. See the full California prefab ADU guide, and the step-by-step ADU permit process.
By Matt Banes, iModular.com. California modular building specialist with 38 years in the industry. Last updated: October 7, 2026. This is general information, not legal advice. Local ordinances can be more generous than state law; check with your city.
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