California Granny Flat Law: Size, Parking, and Permits

California granny flat law, set out in Government Code Sections 65852.2 and 65852.22, gives homeowners a broad right to add accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs) to residential property, and it strips local governments of most of the tools they once used to block these projects.¹ The statute fixes minimum sizes, caps parking demands, forces ministerial permit review, and preempts local zoning that conflicts with its floor. On a single-family lot, you can potentially add up to three separate units.

What Counts as a Granny Flat

State law recognizes three kinds of secondary unit, and the category you build determines nearly everything else about the project.

A detached ADU is a freestanding structure separate from the main house, often built in a backyard or converted from a garage, with its own entrance and full kitchen and bathroom.
An attached ADU shares at least one wall with the primary residence but functions as a self-contained dwelling.
A JADU is no more than 500 square feet, sits entirely within the walls of an existing or proposed single-family home, and must include an efficiency kitchen with a cooking appliance, food prep counter, and storage cabinets. A JADU can share a bathroom with the main house.²

Every ADU has to provide complete independent living facilities, including permanent provisions for sleeping, cooking, eating, and sanitation.¹ The shared-bathroom allowance is unique to the JADU, which is why a converted bedroom or attached garage is the simplest option for many homeowners.

How Many Units You Can Add on One Lot

On a single-family lot, the local agency must allow at least one ADU converted from existing space, one newly constructed detached ADU, and one JADU. That adds up to three additional units on one property, site conditions permitting.³ Multifamily lots can take up to two detached ADUs plus conversions of non-livable space inside the existing building.

There is a ceiling worth knowing. Under SB 9, which allows lot splits and duplexes on single-family lots, no combination of primary units, ADUs, and JADUs may exceed four total units on a single lot.³ Most first-time builders won’t hit that ceiling, but it matters if you plan to add units in stages.

Size, Height, and Setbacks

State law guarantees a floor. No local zoning rule can stop you from building at least an 800-square-foot ADU with four-foot side and rear setbacks, regardless of lot coverage limits, floor area ratio caps, or open space requirements.¹ If your city tries to cap ADUs at 600 square feet or demand ten-foot setbacks, the statute overrides it.

Local ordinances can allow more. An attached ADU can go up to 50 percent of the existing living area or 1,200 square feet, whichever is less. A detached ADU can reach 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

The base height limit for a detached ADU on most residential lots is 16 feet. You can go to 18 feet if the ADU sits within a half-mile walking distance of a major transit stop or high-quality transit corridor, and an additional two feet is allowed to match the roof pitch of the primary dwelling. Eighteen feet is also available on lots with an existing or proposed multifamily, multistory building. An attached ADU can reach 25 feet, or the height of the primary dwelling if that’s lower.³

If those height allowances permit a two-story detached ADU that meets building code, the local agency cannot deny the project just 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 The rule applies to single-family and multifamily lots alike.

Parking

California sharply limits parking demands on ADUs. No additional parking is required if any of the following 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 with a permit for a new primary dwelling on the same lot.³

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

Who Has to Live There, and What You Can Rent

Owner-occupancy rules depend on which unit type you build. AB 976 permanently eliminated local owner-occupancy requirements for standard ADUs, so your city cannot require you to live on the property as a condition of building or renting one.⁴ You can rent the main house and the ADU to separate tenants.

JADUs work differently. When a JADU exists on the property, the owner must live on-site, either in the main house or in the JADU itself. The only exception is for properties owned by a government agency, land trust, or housing organization.² If your plan is to rent both dwellings and live elsewhere, a standard ADU is the right form.

Short-term rentals are off the table. Both ADUs and JADUs are barred from stays of less than 30 consecutive days.¹ Rental income from a long-term tenant is taxable at the federal level, and a tax professional can walk you through deductions and depreciation for residential rental property.⁵

The Permit Process and Timelines

ADU permits go through ministerial review. If the project meets the objective development and building code standards, the local agency must approve it. There is no discretionary review, no public hearing, and no chance for neighbors to formally object.⁶ Your project cannot be blocked because a neighbor dislikes a two-story structure next door.

The timeline is strict. The local agency has 60 days to approve or deny a complete application. A completeness determination must arrive within 30 days of submission, and if it doesn’t, the application is deemed complete automatically. If the agency misses the 60-day window, the permit is deemed approved.⁶

Expect to submit a site plan showing existing structures and the proposed ADU location, a floor plan of the interior, elevation drawings, and utility connection plans for water, sewer, and electric. Local forms vary, so check with your planning department for its exact submission format before you start drafting. Accurate measurements matter: a site plan that puts the ADU three inches too close to the property line means a revision cycle that resets processing.

Impact Fees and Property Taxes

ADUs of 750 square feet or less and JADUs of 500 square feet or less are exempt from development impact fees. For ADUs larger than 750 square feet, the impact fee must be calculated proportionally, based on the ADU’s square footage relative to the primary dwelling, rather than charged as if it were a new standalone home.³ That proportional rule keeps cities from using impact fees to price ADUs out of reach.

Permit fees beyond impact fees vary by jurisdiction. Ask your local building department for a fee schedule before you finalize the budget.

On property taxes, Proposition 13 protects you from a full reassessment. 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 where it was. 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, and your original home’s assessed value, capped at 2 percent annual growth, is untouched.

Selling an ADU Separately

An ADU historically could not be sold separately from the primary residence. AB 1033, signed in 2023, changed that by authorizing local agencies to adopt ordinances that let ADUs 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. If your city has adopted an AB 1033 ordinance, you can sell the ADU to a different buyer while keeping the main house. Ask your local planning department whether the option is available where you live.

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
Internal Revenue Service. Publication 527 (2025), Residential Rental Property
6
Association of Bay Area Governments. State Laws Summary for Accessory Dwelling Units and Junior Accessory Dwelling Units