Adding ADUs to a Multifamily Property in California (SB 1211)

If you own an apartment building or other multifamily property in California, state law lets you add two kinds of ADUs: conversions of non-livable space (at least one, up to 25% of the existing units) and new detached ADUs (up to 8, but never more than the number of existing units). SB 1211 raised the detached limit from 2 to 8 starting in 2025, and it stopped cities from requiring replacement parking when uncovered spaces become ADUs.

Key takeaways

• ›Conversions: at least 1 ADU, and up to 25% of the existing unit count, from storage rooms, attics, basements, garages, and similar non-livable space.
• ›Detached: up to 8 ADUs on a lot with an existing multifamily building, but not more than the number of existing units. On a lot with a proposed multifamily building, the limit is 2.
• ›Cities can't require you to replace parking lost when uncovered parking is converted to ADUs (SB 1211).
• ›Existing tenants may have rights under AB 1482 or a local rent ordinance, so check those before you take away storage or parking.

How many ADUs can you add to a multifamily lot in California?

Government Code §66323 sets two separate allowances that you can combine.

1. Conversion ADUs. Cities must allow ADUs inside portions of an existing multifamily building that aren't used as living space, such as storage rooms, boiler rooms, passageways, attics, basements, and garages. You get at least one, and up to 25% of the existing units.

2. Detached ADUs. On a lot with an existing multifamily dwelling, cities must allow up to 8 detached ADUs, but not more than the number of existing units. Before SB 1211 took effect in 2025, the limit was 2. On a lot with a proposed (not yet built) multifamily dwelling, the limit is 2 detached ADUs.

Here's how the totals work at different building sizes:

Fractions are typically rounded down, so a 6-unit building gets 1 conversion ADU (25% of 6 is 1.5), not 2. Check how your city rounds.

What rules apply to detached ADUs on a multifamily lot?

• ›Height. Detached ADUs on a lot with a multistory multifamily building can be 18 ft tall. If the lot is also within half a mile of major transit, state law adds up to 2 ft so the ADU roof can match the main building's pitch.
• ›Setbacks. Side and rear setbacks can be no more than 4 ft for new ADUs.
• ›Parking. Under SB 1211, cities can't require you to replace uncovered parking spaces converted to ADUs. Garage parking lost to an ADU also doesn't need replacing, and no parking is required for an ADU within half a mile walk of public transit.
• ›Review. ADU applications are ministerial. The city has 15 business days to decide whether your application is complete and 60 days to approve or deny a complete application, with no public hearing (SB 543).
• ›Fees. No impact fees on ADUs under 750 sq ft, and no school impact fees at 500 sq ft or less.

For the full statewide baseline, see our guide to California ADU laws and our explainer on ADU setback requirements.

Example: a 6-unit building in Long Beach

Say you own a 6-unit, two-story apartment building in Long Beach with a rear parking area of uncovered spaces and a ground-floor storage room.

What you can add:

• ›Detached ADUs: up to 6. The limit is 8, but you can't exceed the 6 existing units.
• ›Conversion ADUs: 1. 25% of 6 is 1.5, which typically rounds down to 1. You could convert the storage room.
• ›Total: up to 7 ADUs, taking the property from 6 units to 13.

Height: Our Long Beach data lists 18 ft for detached ADUs on a lot with a multistory multifamily dwelling. Long Beach has no local ADU ordinance of its own and reviews ADUs directly under state law.

Parking: If the detached ADUs go on the uncovered parking area, SB 1211 bars the city from requiring those spaces to be replaced.

Rough numbers: Based on our Long Beach data as of 2026, ADU build costs run $150,000–$420,000 per unit and ADU rents run $1,700–$3,800 a month. At the low end of rent, 7 ADUs would bring in about $11,900 a month in gross rent before vacancy, taxes, and maintenance. Smaller units under 750 sq ft also avoid impact fees. Run your own figures with the cost calculator and ROI calculator.

What about existing tenants, rent control, and AB 1482?

Adding ADUs doesn't change the rules that protect the tenants already living in the building. Before you start:

• ›Check whether your building is covered by AB 1482, California's Tenant Protection Act, or by a local rent control ordinance. Many cities, including Los Angeles, Oakland, San Francisco, and Santa Monica, have their own rent rules.
• ›Watch for reduced services. If tenants currently use the storage room, garage, or parking you plan to convert, removing it may count as a reduction in housing services under a local rent ordinance, which can affect the rent you're allowed to charge.
• ›Plan construction impacts. Noise, access, and utility shutoffs can trigger notice requirements.

In San Francisco, for example, our city data notes that the Local ADU program allows larger units inside an existing building but triggers city tenant protections. Read your local rent ordinance, or talk to a landlord-tenant attorney, before you file plans.

How do you finance ADUs on a multifamily property?

Financing multiple ADUs on an apartment building usually looks different from a single backyard unit:

• ›Buildings with 5 or more units are generally financed as commercial property, so expect commercial loan terms and an appraisal based on the building's income.
• ›Cash-out refinance or a construction loan can fund several units at once. Lenders will want plans, a contractor bid, and projected rents.
• ›Phasing can help. Building the conversion ADU first, then the detached units, lets new rent support the next phase.

Our ADU financing guide covers the main loan types, and the financing calculator estimates monthly payments. Note that the CalHFA ADU grant has been closed since December 2023, with no new round announced.

Where to start in your city

Local ordinances must meet state law, but details like design standards and fees vary. San Jose allows ADUs on multifamily properties, and Sacramento and San Diego each publish their own ADU rules. Compare cities on the California ADU hub or side by side with our comparison tool.

Sources

• ›SB 1211 (2024): ADUs on multifamily lots
• ›California Government Code §66323: number of ADUs allowed per lot
• ›California Government Code §66321: ADU size and height
• ›HCD: Accessory Dwelling Units
• ›Long Beach cost and rent figures: ADUByCity city data for Long Beach, as of 2026