California ADU Law: Size Limits, Parking, and Approval Deadlines

California ADU laws require every city and county to allow accessory dwelling units on residential property, and the statewide standards override any local rule that would make building one impractical. Government Code Section 65852.2, reorganized in 2024 into new code sections starting at 66314, sets minimum size, setbacks, height, and parking that no local ordinance can undercut. The same framework caps impact fees, imposes a hard approval deadline, and limits what homeowners associations can do to block a project.

How Many ADUs Are Allowed per Lot

On a single-family lot, the local agency must allow at least one ADU converted from existing space such as a garage, one newly built detached ADU, and one junior accessory dwelling unit. A single-family property can potentially carry three additional housing units beyond the main home.¹

Multifamily properties get more. Local agencies must allow at least one ADU converted from existing non-livable space (or up to 25 percent of the existing unit count, whichever is greater), plus two detached ADUs on lots with a proposed multifamily building, or up to eight detached units on lots with an existing multifamily building, capped at the number of existing units on the lot.¹

Size, Setback, and Height Minimums the City Must Allow

A local government cannot set a maximum size below 850 square feet for a studio or one-bedroom ADU, or below 1,000 square feet for a unit with two or more bedrooms. The ceiling for a detached ADU is 1,200 square feet, though a local ordinance may allow more.²

Side and rear setbacks are capped at four feet for new construction. If you convert an existing structure such as a detached garage, or build a new unit in the same footprint and dimensions as that existing structure, no setback is required at all.²

Height depends on where the lot sits. Detached ADUs on single-family or multifamily lots can be up to 16 feet tall. That rises to 18 feet if the property is within half a mile of a major transit stop or high-quality transit corridor, or if the lot already has an existing multistory multifamily building. Attached ADUs can reach 25 feet or the height limit that applies to the primary dwelling under local zoning, whichever is lower.¹

A city cannot deny a two-story detached ADU that fits within the allowable height. Even if the underlying zoning restricts the primary home to one story, the ADU height rules operate independently.¹

Junior ADUs and the Owner-Occupancy Rule

A junior accessory dwelling unit is a smaller unit carved out of space inside an existing single-family home, including enclosed areas like an attached garage. JADUs are limited to 500 square feet, and only one is allowed per single-family lot.³

Every JADU must have its own exterior entrance separate from the main home’s front door and an efficiency kitchen with cooking appliances, a food preparation counter, and storage cabinets. The unit can either include its own bathroom or share one with the main residence.³

Unlike a full ADU, a JADU requires owner-occupancy. The property owner must live in either the main house or the JADU itself, unless the owner is a government agency, land trust, or housing organization. As of 2026, if the JADU shares a bathroom with the primary residence, owner-occupancy is always required; if it has its own bathroom, the requirement may be waived.¹

A deed restriction must be recorded against the property prohibiting the separate sale of the JADU from the main home and confirming the unit’s size and attributes.³

Parking Rules and Fee Caps

When parking is required at all, it cannot exceed one space per unit or per bedroom, whichever is less, and the spaces can be tandem on a driveway. Parking requirements disappear entirely in several common situations: the ADU is within half a mile walking distance of public transit, the unit is converted from an existing structure, on-street parking permits are required but not offered to the ADU occupant, or a car-share vehicle is stationed within one block.²

If you demolish or convert a garage, carport, or covered parking structure to build an ADU, the local agency cannot require you to replace those lost parking spaces. This provision matters in practice because replacing off-street parking on a small urban lot can easily kill a project.²

Impact fees follow a two-tier rule. An ADU under 750 square feet owes zero impact fees to any local agency, special district, or water corporation. For units at 750 square feet or above, impact fees must be proportional to the ADU’s square footage relative to the primary dwelling, which typically results in a fraction of what a standalone home would be charged.²

The impact fee exemption does not cover utility connection or capacity charges. Water and sewer hookup fees can range from a few thousand dollars to $35,000 or more depending on the local utility provider, so budget for those separately even when the ADU qualifies for the impact fee waiver.

The 60-Day Approval Deadline

Local agencies must approve or deny a complete ADU application within 60 calendar days. If the agency misses that window, the application is deemed approved by operation of law. No action within 60 days means the homeowner has an approved permit.¹

The key word is “complete.” The clock starts when the application includes all required documentation and fees. If the planning department flags your submission as incomplete, the 60-day period does not begin running until you supply the missing items. This is where most delays actually happen. A missing structural calculation or Title 24 energy compliance report gives the agency a legitimate reason to pause the timeline.

A typical application package includes a site plan showing all structures on the lot, detailed floor plans for the ADU, structural engineering calculations, Title 24 energy compliance documentation, the property owner’s information, and the contractor’s state license number.⁴

Renting an ADU

California does not require owner-occupancy for standard ADUs. You can own a property with an ADU and rent out both the main house and the ADU to tenants without living on-site.¹

Short-term rentals work differently. Local agencies may require that ADU rentals be for terms longer than 30 days. As of January 1, 2026, JADUs are also subject to a minimum 30-day rental term and can no longer be listed on short-term hosting platforms.¹

If your local jurisdiction adopts the 30-day minimum, listing the unit on nightly or weekly platforms would violate your permit conditions. Check your city’s ordinance before committing to a short-term rental model.

HOA Restrictions

California Civil Code Section 4751 makes any HOA covenant or CC&R provision void and unenforceable if it effectively prohibits or unreasonably restricts the construction or use of an ADU or JADU on a single-family lot. An HOA cannot ban ADUs outright, and it cannot impose rules so burdensome that they amount to a ban in practice.⁵

The law allows “reasonable restrictions,” defined as rules that do not unreasonably increase construction costs, effectively prohibit construction, or destroy the ability to build a unit that otherwise complies with state ADU law. An HOA might regulate exterior paint colors or fence heights, but it cannot require design standards so expensive that they price the project out of reach.⁵

Selling an ADU Separately From the Main Home

Historically, an ADU could not be sold independently of the primary residence. AB 1033, signed into law in October 2023, changed that by allowing local agencies to adopt ordinances permitting the separate sale of a primary dwelling and its ADU as condominiums. This is not a statewide mandate. Each city or county must opt in by passing its own local ordinance authorizing the condominium conversion.

Where a jurisdiction has adopted such an ordinance, the ADU and main home are treated as separate condominium units, each with its own title. JADUs remain subject to a deed restriction prohibiting separate sale regardless of local ordinances.³

Fire Sprinkler Requirements

Whether an ADU needs fire sprinklers depends on the main home. If the existing primary residence was not required to have an automatic fire sprinkler system, the ADU is exempt as well, provided the detached unit does not exceed 1,200 square feet. If the main home already has sprinklers, the ADU must also be sprinklered.⁶

When both a new primary home and ADU are built at the same time, sprinklers are required in both structures under the California Residential Code. The sprinkler exemption applies only to ADUs added to an existing home that was itself exempt. The trigger is the primary dwelling’s status, not the ADU’s size.⁶

1
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook
2
California Legislative Information. California Code Government Code 65852.2
3
California Legislative Information. California Code Government Code 65852.22
4
California Energy Commission. 2025 Energy Code Accessory Dwelling Units (ADU) FAQs
5
California Legislative Information. California Code CIV 4751
6
California Department of Housing and Community Development. California State Fire Marshal Information Bulletin 17-001