California ADU Legislation: Unit Limits, Permits, and Fees

California ADU laws give homeowners a state-backed right to add an accessory dwelling unit on nearly any residential lot, and they cap what cities and counties can require for size, height, setbacks, parking, and permit timelines. A run of legislation since 2016 pulled these rules out of local hands and set statewide floors, with 2024 changes making the elimination of owner-occupancy permanent and opening a path to sell ADUs as condominiums. Updates effective in 2026 added new permit-processing deadlines and tightened rental rules for junior units. If you own a residential property with a primary home on it, you almost certainly have the right to add at least one more unit.

How Many Units You Can Add

On a single-family lot, the local agency must allow one detached newly constructed ADU, one ADU converted from existing space such as a garage, and one Junior ADU on the same property.¹ That is up to three additional units alongside the main house.

Multifamily properties follow a different formula. Local agencies must permit at least one ADU converted from existing non-livable space, or up to 25 percent of the existing unit count, whichever is greater. On top of that, up to two detached ADUs are allowed on a lot with a proposed multifamily building, or up to eight detached ADUs on a lot with an existing multifamily building, capped at the number of existing units on the lot.¹ Junior ADUs are not available on multifamily lots.

The Four Types of ADU

The type you choose drives cost, size limits, and which relaxed rules apply.

Detached ADU: a standalone structure separated from the main home, with the most design freedom and a size cap of 1,200 square feet.
Attached ADU: shares at least one wall with the primary dwelling, capped at 1,200 square feet or 50 percent of the primary home’s floor area, whichever is smaller.
Conversion ADU: built inside an existing garage, barn, or other non-livable space, and eligible for a zero-setback rule that new construction does not get.
Junior ADU (JADU): capped at 500 square feet, built entirely within the existing walls of a single-family home or an attached structure like a garage, and must include an efficiency kitchen with cooking appliance, counter, and storage cabinets. A separate bathroom is optional; the JADU can share one with the main house.²

One catch on JADUs: the property owner must live in either the main house or the JADU. Governmental agencies, land trusts, and housing organizations are exempt from that requirement.³

Size, Height, and Setbacks

State law sets a floor no city can go under. A local agency can impose its own size cap, but that cap cannot be smaller than 850 square feet for a studio or one-bedroom ADU, or 1,000 square feet for an ADU with two or more bedrooms.⁴

Height

A detached ADU on a single-family or multifamily lot gets a baseline height of 16 feet. That rises to 18 feet if the lot sits within a half-mile walking distance of a major transit stop or high-quality transit corridor, with an additional two feet allowed to match the primary home’s roof pitch. Detached ADUs on lots with an existing multistory multifamily building also get the 18-foot allowance.¹ An attached ADU can reach 25 feet, or the local zoning height limit for the primary dwelling, whichever is lower, and local agencies cannot require an attached ADU to exceed two stories.⁴

Setbacks

For newly built ADUs, the maximum setback a local agency can require is four feet from the side and rear lot lines.⁴ Conversions get a better deal. If you convert an existing garage, accessory structure, or living area into an ADU, no setback is required. The same zero-setback rule applies if you demolish an existing structure and rebuild in the same footprint and dimensions.¹ On a tight lot, that difference can decide whether the project pencils out.

Parking

Parking for an ADU is capped at one space per unit or one space per bedroom, whichever produces fewer spaces. Many ADUs will not require any new parking. If a garage, carport, or covered parking structure is demolished or converted to create the ADU, the local agency cannot require you to replace those lost spaces.⁴ Separately, AB 2097 prohibits any minimum parking requirement for residential projects within a half-mile of a major transit stop, which sweeps in a large share of urban and suburban properties.⁵

Owner-Occupancy and Rentals

For standard ADUs, the owner-occupancy requirement is gone for good. The original prohibition on local agencies requiring the owner to live on-site was set to expire on January 1, 2025, but AB 976 made it permanent before that sunset arrived.⁶ You can own the property, rent both the main house and the ADU, and live somewhere else. JADUs are the exception, since they carry their own owner-occupancy rule described above.

Short-term rentals are a separate question. Local agencies can require that ADU rentals run longer than 30 days, and effective January 1, 2026, JADUs are prohibited from short-term rental use and must be rented for terms longer than 30 days if rented at all.¹ If your plan involves nightly rentals, check the local ordinance first. Many cities already ban short-term ADU rentals, and state law lets them.

Tenant Protections

The Tenant Protection Act (AB 1482) caps annual rent increases and requires just-cause eviction for most residential tenancies. Single-family owner-occupied residences where the owner rents no more than two units or bedrooms are exempt from the just-cause provisions, and ADUs and JADUs are specifically named in that exemption.⁷ For the rent cap exemption, the property generally must be owned by a natural person rather than a corporation or certain LLCs, and the tenant must receive written notice that the property is exempt. If you don’t live on the property, those owner-occupant exemptions won’t apply and the full Act likely covers your tenants.

Impact Fees and Property Taxes

ADUs under 750 square feet of interior livable space are fully exempt from impact fees. JADUs under 500 square feet are also exempt. For ADUs at 750 square feet or larger, impact fees must be proportional to the square footage of the primary dwelling, which usually produces a much smaller charge than a standalone home of the same size would face. School fees follow similar logic: ADUs and JADUs under 500 square feet don’t increase assessable space for school fee calculations.¹

Building an ADU triggers a property tax reassessment, but only on the value of the new construction. The assessed value of your existing home and land stays unchanged. The county assessor estimates the market value the ADU adds and applies taxes only to that increment.⁸ For most owners, that means the tax bill rises by a few thousand dollars a year rather than resetting the whole property to current market value. The distinction matters for anyone who bought years ago and benefits from Proposition 13’s annual cap on assessed value growth.

The Permit Process

ADU permits are reviewed ministerially. The local agency applies a checklist of objective standards rather than holding a public hearing or exercising subjective judgment. If your plans meet the standards, the permit must issue. The agency has 60 days from receiving a complete application to approve or deny, and if it misses that deadline, the application is deemed approved.¹

Starting in 2026, a front-end checkpoint was added. The permitting agency must decide whether your application is complete and notify you in writing within 15 business days of receiving it. If your application is found incomplete or denied, the agency must offer an appeal process, with a final written determination due within 60 business days of receiving the appeal.¹ Agencies can no longer stall indefinitely by repeatedly requesting more materials.

What Your Application Needs

Specific requirements vary by jurisdiction, but most building departments expect a site plan showing existing structures, property lines, and the proposed ADU footprint, plus floor plans, elevations, and structural details sufficient to confirm compliance with the California Building Standards Code. A Title 24 energy compliance report is standard for new construction or a major conversion, showing that insulation, windows, HVAC, and lighting meet California’s energy efficiency requirements.⁹ For detached ADUs, review fire separation distance rules. A structure within five feet of a property line or another building generally needs a one-hour fire-rated wall, and structures within three feet cannot have windows or doors on the fire-rated side.

Selling an ADU Separately

AB 1033, effective January 1, 2024, opened a path to sell an ADU as a separate condominium unit. It is not automatic. Your local agency must first adopt an ordinance allowing separate ADU conveyances, and the process requires creating a condominium under the Davis-Stirling Common Interest Development Act and complying with the Subdivision Map Act.¹⁰

Before recording the condominium plan, the ADU must pass a safety inspection, documented by either a certificate of occupancy from the local agency or a housing quality standards report from a HUD-certified building inspector. Every existing lienholder must consent to the condominium plan in writing, and a lienholder can refuse.¹⁰ If your property is in an existing homeowners association, the association’s express written authorization is also required before recording the plan. The process is more involved than a typical home sale, but it creates a category of smaller ownership units at price points below what a standalone house costs in most California markets.

1
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
2
California Legislative Information. California Government Code 65852.22
3
California Legislative Information. California Code Government Code 65852.22
4
California Legislative Information. California Code Government Code 65852.2
5
California Department of Housing and Community Development. AB 2097 Transit Distance Criteria
6
California State Assembly. AB 976 – Ting
7
California Legislative Information. AB 1482 Tenant Protection Act of 2019
8
California State Board of Equalization. New Construction – Property Tax
9
Energy Code Ace. 2022 Title 24, Part 6 – Single-family Buildings Accessory Dwelling Units
10
California Legislative Information. AB 1033