California Granny Flat Law: Permits, Parking, and Property Tax

California granny flat law gives most homeowners the right to add an accessory dwelling unit on residential property, and it sharply limits how much your city can stand in the way. The core rules sit in Government Code Sections 65852.2 and 65852.22, which set statewide standards for accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs), from maximum size to how fast your city must act on a permit.¹ On a single-family lot, you can potentially add up to three separate units under current law.

The Three Types of Units

California recognizes three categories of granny flat, and each one carries different physical requirements.

A detached ADU is a freestanding structure separate from the main house, often built in a backyard or converted from a garage. It needs its own entrance and full kitchen and bathroom facilities.

An attached ADU shares at least one wall with your primary residence. It functions as a self-contained dwelling but is physically integrated into the main structure.

A junior ADU, or JADU, is a smaller unit of no more than 500 square feet, contained entirely within the walls of an existing or proposed single-family home. A converted bedroom or attached garage is the typical approach. JADUs must include an efficiency kitchen with a cooking appliance, a food preparation counter, and storage cabinets, but they can share a bathroom with the main house.²

Every ADU must provide complete independent living facilities with permanent provisions for sleeping, cooking, eating, and sanitation.¹ The JADU is the exception on the bathroom, which makes it the simplest conversion when you’re working with an existing floor plan.

How Many Units You Can Add

On a single-family lot, state law requires local agencies to allow at least one ADU converted from existing space, one newly constructed detached ADU, and one JADU. That adds up to three potential new units on one property, site conditions permitting.³ On multifamily lots, the rules allow up to two detached ADUs plus conversions of non-livable space within the existing building.

One ceiling to watch. Under SB 9, which allows lot splits and duplexes on single-family lots, no combination of primary units, ADUs, and JADUs can exceed four total units on a single lot.³ A homeowner building their first granny flat usually won’t hit this limit, but it matters if you’re planning multiple additions over time.

Size, Height, and Setbacks

State law guarantees that no local government can impose zoning rules that prevent you from building at least an 800-square-foot ADU with four-foot side and rear setbacks. That protection applies regardless of local lot coverage limits, floor area ratio caps, or open space requirements.¹ If your city tries to cap ADUs at 600 square feet or impose 10-foot setbacks, state law overrides those restrictions.

Cities can allow larger units. Under the statute, an attached ADU can reach up to 50 percent of the existing living area or 1,200 square feet, whichever is less. A detached ADU can go up to 1,200 square feet.¹ Your city may set its own maximum somewhere between 800 and 1,200 square feet, but it cannot go below 800.

Height Limits

Height rules for detached ADUs follow a tiered system:

16 feet is the base limit for a detached ADU on most residential lots.
18 feet is allowed if the ADU is within a half-mile walking distance of a major transit stop or high-quality transit corridor, with an additional two feet permitted to match the roof pitch of the primary dwelling.
18 feet is also allowed on lots with an existing or proposed multifamily, multistory building.
25 feet is the maximum for an attached ADU, or the height of the existing primary dwelling if that is lower.³

If those height allowances permit a two-story detached ADU that meets building code, your local agency cannot deny the project simply because underlying zoning restricts primary dwellings to one story.³

Setbacks

Converting an existing garage or accessory structure into an ADU requires no setback at all. For new construction that isn’t replacing an existing structure in the same footprint, the maximum setback a local agency can require is four feet from side and rear lot lines.¹ This applies to both single-family and multifamily lots.

Parking Rules

California sharply limits the parking a city can require for an ADU. No additional parking spaces are required when any of the following conditions apply:

The ADU is within a half-mile walking distance of public transit.
The ADU is within an architecturally or historically significant district.
The ADU is part of the existing primary residence or an accessory structure.
On-street parking permits are required in the area but not offered to the ADU occupant.
A car-share vehicle is located within one block.
The ADU application is submitted alongside a permit for a new primary dwelling on the same lot.³

When none of those exemptions apply, local agencies can require at most one parking space per ADU or per bedroom, and those spaces can be provided as tandem parking on an existing driveway.¹ If you demolish a garage or carport to build the ADU, the city cannot require you to replace those lost parking spaces.

Who Has to Live on the Property

The owner-occupancy picture depends on which type of unit you build.

For standard ADUs, AB 976 permanently eliminated local owner-occupancy requirements. Your city cannot require you to live on the property as a condition of building or renting an ADU.⁴ You can rent the main house and the ADU to separate tenants.

JADUs are different. The law still requires the property owner to live on-site when a JADU exists on the property. You can live in either the main house or the JADU, but one of the two must be your residence. The only exception is for properties owned by a government agency, land trust, or housing organization.² If you want to rent both dwellings without living there, a standard ADU is the path that allows it.

Both ADUs and JADUs are prohibited from being used as short-term rentals for stays of less than 30 consecutive days.¹ These units are meant to add to long-term housing stock, not become vacation rentals.

The Permit Process

ADU permits go through ministerial review, which means your local agency must approve the project if it meets the objective development and building code standards. No discretionary review, no public hearing, and no formal opportunity for neighbors to object or stall the application.⁵ In practice, your project cannot be blocked because a neighbor doesn’t want a two-story structure next door.

The timeline is strict. Once you submit a complete application, the local agency has 60 days to approve or deny the permit. A completeness determination must come within 30 days of submission. If the agency doesn’t respond within 30 days, the application is automatically deemed complete.⁵ If the agency fails to act within the 60-day window, the permit is deemed approved.

Every city’s forms look slightly different, but expect to prepare a site plan showing all existing structures and the proposed ADU location, a floor plan of the unit’s interior layout, and elevation drawings showing the structure’s height and appearance from each side. Plans for utility connections to water, sewer, and electrical services are standard. Check with your local planning department early for its specific submission format.

Fees and Construction Costs

ADUs of 750 square feet or less and JADUs of 500 square feet or less are completely exempt from development impact fees. For ADUs larger than 750 square feet, impact fees must be calculated proportionally based on the ADU’s square footage relative to the primary dwelling, rather than at the same flat rate as a new standalone home.³ That proportional rule prevents cities from using impact fees to make ADUs financially impractical.

Permit fees beyond impact fees vary by jurisdiction and can range from a few hundred dollars for a simple JADU conversion to several thousand for a large detached ADU involving new utility connections. Construction costs in California typically run between $300 and $600 per square foot for new ADU construction, depending on location, materials, and finishes. A 500-square-foot detached unit might cost $150,000 to $300,000, while a larger 1,000-square-foot build could reach $400,000 or more. Garage conversions and JADUs tend to cost less because you’re working within an existing structure, though electrical upgrades, plumbing additions, and fire separation work still add up.

Property Tax Effects

Under Proposition 13, building an ADU does not trigger a full reassessment of your entire property. The county assessor performs a blended assessment: only the value of the new construction is added to your existing assessed value. The assessment on your primary home stays the same. With California’s combined property tax rate near 1 percent in most areas, an ADU that cost $250,000 to build would add roughly $2,500 per year in property taxes. Your existing home’s assessed value, and its annual increase capped at 2 percent, remains untouched.

Selling an ADU Separately

For years, an ADU could not be sold separately from the primary residence. AB 1033, signed into law in 2023, changed that by authorizing local agencies to adopt ordinances allowing ADUs to be sold as separate condominiums. Not every city has opted in, and the process requires a condominium map and compliance with local condominium conversion rules. Where a city has adopted an AB 1033 ordinance, you can sell the ADU to a different buyer while keeping the main house. Check with your local planning department to see whether this option is available in your jurisdiction before you count on it.

1
California Legislative Information. California Government Code 65852.2
2
California Legislative Information. California Government Code 65852.22
3
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
4
California State Assembly. AB 976 – Ting
5
Association of Bay Area Governments. State Laws Summary for Accessory Dwelling Units and Junior Accessory Dwelling Units