On a single-family lot in California, state law guarantees up to three accessory units in the right combination: one ADU converted from existing space, one new detached ADU and one JADU inside the house. Starting January 1, 2027, AB 956 lets you build two detached ADUs instead, though the city then doesn’t have to approve a JADU. On an existing multifamily lot, you can add up to eight detached ADUs (never more than the number of existing units) plus conversions of up to 25% of the unit count.
This is one of the first questions buyers ask me, and the answer depends on the type of lot, how you build the units and which year you pull permits. Here’s the full breakdown, with the unit counts in tables.
How Many ADUs on a Single-Family Lot?
The state minimums are in Government Code 66323. A city has to approve these combinations ministerially, meaning no hearing:
| Combination (2026) | Main home | Accessory units | Total homes |
|---|---|---|---|
| One ADU only (attached, detached or conversion) | 1 | 1 | 2 |
| One JADU only | 1 | 1 | 2 |
| Conversion ADU + JADU | 1 | 2 | 3 |
| Conversion ADU + detached ADU + JADU | 1 | 3 | 4 |
The key is that the conversion ADU and the JADU come from existing space, like a garage or part of the house. The detached unit is new construction. A city has to allow that new detached unit up to at least 800 square feet with 4-foot side and rear setbacks, even if lot coverage or floor area limits would otherwise block it.
Some cities write their own codes to match. Costa Mesa’s ADU code, for example, allows one detached ADU, one conversion ADU and one JADU on a single-family lot. Others write it more narrowly, but state law controls where they conflict.
What Changes in 2027: Two Detached ADUs (AB 956)
Governor Newsom signed AB 956 on September 29, 2026. Starting January 1, 2027:
- A city must approve two detached, new-construction ADUs on a single-family lot, if each meets size, height and setback rules.
- On a lot with two detached ADUs, the city doesn’t have to also approve a JADU.
- HOAs can’t block ADUs that comply with state law.
I go deeper in AB 956: Two Detached ADUs in California. With two detached units, lot coverage becomes the limit you hit first. Lot Coverage and Multiple ADUs runs the math on real lot sizes.
How Many ADUs on a Multifamily Lot?
| Lot type | Detached ADUs | Conversion ADUs (non-living space) |
|---|---|---|
| Existing multifamily (2+ units) | Up to 8, but not more than the existing unit count | Up to 25% of existing units, at least 1 |
| Proposed (new) multifamily | Up to 2 | N/A |
So an existing fourplex can add up to four detached ADUs plus one conversion ADU, for up to nine homes on the lot. JADUs aren’t allowed on multifamily properties. I explain each rule in How Many ADUs Can You Add to a Multi-Unit Property, The 25% Rule for Garage Conversions and Can You Build a JADU on a Multifamily Property?
Adding SB 9 to the Count
SB 9 is a separate law. It lets you build two primary units on a single-family lot, or split the lot in two. A city can limit ADUs on SB 9 lots. On a lot split, many cities cap each new parcel at two units total, including ADUs. So the realistic SB 9 lot-split maximum is often four homes across both parcels. More in What Is SB 9 in California? and How Does SB 9 Work With ADUs?
The City of Los Angeles is its own case. Its ZA Memo 143 opens a path to four units on a single-family lot without a lot split. See ZA Memorandum No. 143.
More Units Isn’t Always More Money
The law sets the maximum. The numbers decide what you should build. I underwrite every plan the same way: total monthly payment (PITI) against total rent.
- Construction cost scales with each unit. A second detached ADU adds a full build budget, not a discount.
- Fees. Under SB 1117, impact fees apply only above 750 square feet for the first two ADUs. Additional ADUs are assessed on the full size.
- Parking, utilities and sewer get harder with each unit.
- Livability. Four homes on a 6,000 square foot lot can rent for less per unit than three well-spaced ones.
For the bigger state picture, see California ADU Laws 2026, or the HCD ADU page for the official source.
Frequently Asked Questions
How many ADUs are allowed on one property in California?
On a single-family lot, up to three accessory units: a conversion ADU, a detached ADU and a JADU. On an existing multifamily lot, up to eight detached ADUs (no more than the existing units) plus conversions.
Can I build two detached ADUs?
Starting January 1, 2027, yes. AB 956 requires cities to allow two detached ADUs on a single-family lot. Some cities already allow it locally.
Can I have an ADU and a JADU?
Yes. A JADU is created inside the main home and can be combined with an ADU on a single-family lot.
Can my city limit the number of ADUs?
Not below the state minimums. Cities can allow more, and they can limit ADUs on lots created through SB 9.
Find the Lot That Fits the Unit Count You Want
The number of units you can build depends on the lot as much as the law. I’ll help you find a property where the plan you want actually fits.
👉 Book a buyer ADU consult call to go through your options with Dylan
Prefer to talk now? Call Dylan Serna, ADU Realtor at 714-860-2868.
Dylan Serna | The ADU Realtor | eXp Realty | DRE #02217359
This post is general information, not legal advice. Confirm the rules for any specific property with the city.
