How Many ADUs Can I Build on My Lot in California in 2026?

The short answer is three on a single-family lot and up to eight on an apartment lot. The longer answer matters because the numbers changed twice in two years, and a lot of city handouts, designer websites and even some contractors are still quoting the 2023 rules.

Here is the count as it stands in October 2026.

The count, by lot type

Lot	What state law guarantees	Main limits
Single-family, existing house	1 converted ADU + 1 new detached ADU + 1 JADU	Detached up to 800 sq ft with 4-ft side and rear setbacks; JADU up to 500 sq ft inside the house
Single-family, SB 9 lot split	Up to 2 units per resulting lot, ADUs included	Max 4 units across the original lot
Existing multifamily (2+ units)	Up to 8 detached ADUs, not more than existing units	Plus conversions of non-livable space, at least 1 and up to 25% of existing units
Proposed multifamily	Up to 2 detached ADUs	Conversion rules apply once built

A city can always be more generous. It cannot be stricter for the units in the middle column.

Single-family lots: the three-unit combination

California's ADU statute was reorganized in 2024 into Government Code sections 66310 through 66342, and the provision that matters most for an ordinary house is section 66323, the so-called exemption ADUs. These are units a city must approve ministerially if they meet the state's own size and setback numbers, regardless of its local lot coverage or floor-area rules.

The three pieces that can be combined:

• A converted ADU inside the existing house or an existing accessory structure such as a garage. This is the cheapest route when the shell is sound, usually $100,000–$200,000 for a garage — see garage conversion costs.
• A new detached ADU of up to 800 square feet with four-foot side and rear setbacks. A typical 600–800 sq ft detached unit runs $150,000–$350,000 in Los Angeles.
• A JADU of up to 500 square feet carved out of the main house, typically $40,000–$100,000. The differences are in ADU vs JADU.

These are typical Los Angeles market ranges, not a quote.

SB 543, chaptered in October 2025 and in effect since January 1, 2026, did two quiet but important things here. It confirmed that the three can be stacked on one lot, and it changed how size is measured. Every square-foot limit in the statute now refers to interior livable space rather than the exterior footprint, so wall thickness no longer eats into an 800-square-foot cap.

Multifamily lots: SB 1211

SB 1211 took effect January 1, 2025, and it changed the arithmetic for apartment owners more than anything since the ADU laws began. On a lot with an existing multifamily building, you can now add up to eight detached ADUs, but never more than the number of existing units. A duplex gets two, a fourplex four, a twelve-unit building eight.

On top of that, non-livable space inside the building — storage rooms, boiler rooms, laundry rooms, garages — can be converted into ADUs, at least one and up to 25 percent of the existing unit count. And when a carport or surface lot is used for the new units, the city cannot require the lost parking to be replaced.

For owners of older fourplexes and courtyard buildings, this is where the numbers get interesting. It is also where the site work gets expensive: utility capacity for four new kitchens, fire access, and the trenching. A rough feasibility check before drawings saves the most money.

What else changed for 2026

Fees. ADUs of 750 square feet or less still cannot be charged development impact fees. SB 543 also treats units under 500 square feet of interior livable space as not adding assessable space for school fees, which in LAUSD territory is real money — we worked through the numbers in what an ADU permit costs.

Timelines. Cities now have 15 business days to say whether an ADU application is complete. Silence means it is deemed complete.

JADU owner-occupancy. Under AB 1154, the owner must live on site only when the JADU shares a bathroom with the main house. A JADU with its own bathroom does not trigger it, and JADU rentals must run longer than 30 days.

Where cities still say no

State law sets a floor, not a site plan. The things that still stop or shrink ADUs in Los Angeles:

• Fire zones and narrow streets. Pasadena limits about 1,600 hillside lots on streets 26 feet wide or narrower to the exemption ADUs only. We covered the rest of Pasadena's ADU rules on our Pasadena ADU builder page.
• Protected trees. Native oaks and sycamores can fix the footprint long before zoning does.
• Utilities. A 100-amp panel and an old clay sewer lateral are the most common reasons a buildable unit becomes an expensive one.
• Out-of-date ordinances. The state housing department reviews local ADU ordinances and sends findings letters when they fall short. Pasadena received one in February 2025 for, among other things, allowing only one exemption ADU on a single-family lot. Until a city amends its code, its handouts may say less than state law allows.

Is the third unit worth it?

Often the converted ADU or JADU is the most cost-effective unit on the lot, because the shell already exists. Whether a second or third unit pays back depends on rents, financing and how long you plan to hold. We looked at that question in does an ADU add value and the overall budget in what an ADU costs in 2026. New construction is reassessed only for the added value, not the whole property — see will a remodel raise property taxes.

If you are deciding how many units fit on your lot, the useful first step is a site walk with the survey, the panel and the sewer in view. That is how we start every ADU and addition project.

Questions

Can I build two detached ADUs on a single-family lot?

Not as a state-law right. The guaranteed combination on a single-family lot is one converted ADU, one new detached ADU and one JADU. A second new detached unit depends on your city choosing to allow it, and most in the Los Angeles area do not. The exception is an SB 9 lot split, which is a different path with its own cap of two units per resulting lot including any ADUs.

Do I have to live on the property to build an ADU?

For a standard ADU, no. Owner-occupancy for ADUs was removed by AB 976. For a JADU it depends on the bathroom. Since January 1, 2026, under AB 1154, the owner has to live on site only if the JADU shares a bathroom with the main house. A JADU with its own bathroom does not trigger the requirement, and JADUs may only be rented for terms longer than 30 days.

How many ADUs can I add to a fourplex?

Up to four detached ADUs, because SB 1211 caps new detached units at the number of existing units, and up to eight only applies to buildings with eight or more. You can also convert non-livable space such as storage rooms, laundry rooms or garages into at least one ADU, and up to 25 percent of the existing unit count. The city cannot require you to replace parking spaces you build over.

Can my city still block an ADU?

It can apply objective standards such as height, fire-code access and tree protection, and some cities limit larger units in high fire hazard areas. Pasadena, for example, limits lots on hillside streets 26 feet wide or narrower to the statewide exemption ADUs. What a city cannot do is deny the units state law guarantees, and the state housing department sends findings letters when local ordinances fall short, as it did to Pasadena in February 2025.