How Many ADUs Are Allowed in California: Single-Family and Multifamily

On a single-family lot in California, state law requires local agencies to allow up to two accessory dwelling units plus one junior ADU, for a total of four dwellings including the primary home. Multifamily properties can add converted ADUs inside the existing building and, since January 1, 2025, up to eight new detached ADUs on the same lot. Those are the floors set by state law; cities and counties can allow more, but they cannot allow less.

Single-Family Lots: Two ADUs Plus a JADU

On a lot with an existing or proposed single-family home, the jurisdiction must permit all three of the following:

One ADU converted from existing space. This covers garage conversions, basement build-outs, and any repurposing of non-livable space inside the primary residence or an accessory structure.
One newly constructed detached ADU on the same lot.
One junior ADU, capped at 500 square feet, contained within the walls of the single-family residence and equipped with an efficiency kitchen and either its own bathroom or shared access to the primary home’s bathroom.

Stacking those together gives four dwelling units on the parcel: the main home, the converted ADU, the detached ADU, and the JADU.¹

Local jurisdictions can adopt ordinances that allow more units than the state minimum, but they cannot fall below it. If your city’s ADU ordinance is more restrictive than state law, state law controls.

Multifamily Lots: Conversions Plus Up to Eight Detached ADUs

Multifamily properties have two separate allowances, and they stack.

The first path is converting existing non-livable space inside the building. Storage rooms, attics, basements, boiler rooms, and garages can all become ADUs. The number of converted units is capped at 25% of the existing apartment count, and at least one conversion is always permitted regardless of building size.

The second path is new detached construction. Senate Bill 1211, effective January 1, 2025, raised the cap on detached ADUs on a multifamily lot from two to eight. These new units cannot demolish or displace existing rental housing. A 12-unit apartment building, for example, could add eight freestanding ADUs on the same lot while keeping every apartment intact, on top of any conversions permitted under the 25% rule.

Junior ADU Rules That Affect Whether the Fourth Unit Works

The JADU is what pushes a single-family lot from three units to four, and it carries conditions the other ADUs do not. It must sit inside the walls of the single-family residence and cannot exceed 500 square feet. The property owner must live in either the main residence or the JADU itself. That owner-occupancy requirement is waived only when the owner is a governmental agency, land trust, or housing organization.¹

Standard ADUs are different. California permanently eliminated the owner-occupancy requirement for standard ADUs in 2024, so you do not need to live on the property to build one or rent it out.

Both ADUs and JADUs are subject to a 30-day minimum rental term. Short-term rentals through platforms like Airbnb are prohibited. For JADUs, AB 1154 closed a statutory gap on that point effective January 1, 2026.¹

Size Minimums Local Agencies Must Allow

The unit count matters only if the units can actually be built. State law sets minimum sizes that local ordinances cannot cut below. Any local ordinance must allow ADUs of at least 850 square feet, or at least 1,000 square feet for units with more than one bedroom.² In jurisdictions without a compliant ADU ordinance, the default maximum is 1,200 square feet for a new detached ADU.

Attached ADUs can reach up to 50% of the primary dwelling’s floor area, but local rules still cannot restrict them below the 850-square-foot floor (or 1,000 square feet for multi-bedroom units). JADUs are capped at 500 square feet statewide, with no local variation.¹

Height Minimums

State law sets minimum height allowances that local agencies must respect under Government Code section 66321:²

Detached ADU on a standard lot: no local height limit below 16 feet.
Detached ADU within half a mile of a major transit stop or high-quality transit corridor: 18 feet, with an additional two feet allowed to match the roof pitch of the primary home.
Detached ADU on a multistory multifamily lot: 18 feet.
Attached ADU: up to 25 feet, or the height limit that applies to the primary dwelling, whichever is lower. Local agencies are not required to allow an attached ADU to exceed two stories.

Setbacks That Cannot Block the Unit

State law caps side and rear yard setbacks at four feet for both attached and detached ADUs. Local agencies can apply front yard setbacks, but no setback of any kind can prevent construction of an ADU that is at least 800 square feet. If a lot is small enough that standard setbacks would make an 800-square-foot ADU impossible, the setbacks yield.¹

Parking Requirements Rarely Apply

Most ADU projects will not face a parking requirement. State law prohibits parking mandates for an ADU in any of these situations:

The ADU is within half a mile walking distance of public transit.
The ADU is in an architecturally or historically significant district.
The ADU is part of an existing primary residence or accessory structure (a conversion).
A car-share vehicle is available within one block of the ADU.

When parking is required, local agencies can mandate no more than one space per ADU, and tandem parking on an existing driveway is allowed. Converting a garage or carport to an ADU never triggers a replacement parking obligation, so the lost spaces do not have to be rebuilt elsewhere on the lot.¹

HOA Lots Get the Same Count

A homeowners association cannot ban ADU or JADU construction on lots zoned for single-family residential use. California Civil Code section 4751 declares void and unenforceable any CC&R provision, deed restriction, or governing document that effectively prohibits or unreasonably restricts the construction or use of an ADU or JADU.³

The HOA can impose reasonable restrictions, and the statute defines that narrowly. A restriction becomes unreasonable if it significantly increases construction costs, effectively prevents an ADU from being built, or eliminates the homeowner’s ability to construct a compliant unit. Requiring architectural compatibility with the primary home is generally reasonable. Demanding setbacks that make construction physically impossible is not.

Selling an ADU Separately

By default, an ADU cannot be sold as a separate property from the primary residence. AB 1033, signed in 2023, lets a local agency adopt an ordinance allowing the primary home and ADU to be split into separate condominiums and sold independently.⁴ This is an opt-in for cities and counties, not a statewide mandate, and adoption has been slow. A narrow separate-sale path also exists for ADUs built by qualified nonprofit housing organizations under a recorded tenancy-in-common agreement meeting state requirements.

1
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
2
California Assembly Housing and Community Development. Accessory Dwelling Unit Handbook
3
California Legislative Information. California Civil Code 4751
4
California Legislative Information. AB 1033 Accessory Dwelling Units – Local Ordinances – Separate Sale or Conveyance