Fullerton Zoning and ADU Guide for Homeowners and Sellers

Last updated November 13, 2026. Reviewed by the Cash Home Buyers CA team. Information comes from the City of Fullerton and the California Department of Housing and Community Development; sources are listed at the end.

On June 17, 2025, the Fullerton City Council approved Ordinance No. 3343, which amended the city’s zoning rules for accessory and junior accessory dwelling units to comply with state law. The ordinance, which amends Fullerton Municipal Code section 15.17.100, includes a section on legalizing units built before 2020, which makes it especially useful for sellers with an older backyard unit or garage conversion.

Fullerton ADU rules at a glance

How many units Fullerton allows on a lot

Under section 15.17.100.E, a single-family residential lot, including O-P zoned properties improved with a single-family home, may have one ADU and one JADU. On R-1 and R-2 properties of at least one acre with a single-family home, the city allows up to two detached ADUs, or one attached and one detached ADU. Multifamily lots follow separate subsections that allow conversions and detached units.

Size limits

Section 15.17.100.F.4 says an ADU can be no smaller than an efficiency dwelling unit under Health and Safety Code section 17958.1. Attached ADUs are limited to 850 square feet for a studio or one-bedroom and 1,000 square feet for two or more bedrooms.

Detached ADUs may be up to 1,200 square feet, with an exception for converting an existing accessory structure that is already larger. Interior ADUs have no size limit, and a homeowner who builds a new house may designate an existing single-family home of 1,200 square feet or less as the ADU. A JADU may not exceed 500 square feet.

Height, setbacks and parking

Detached ADUs may be 16 feet tall, 18 feet within a half-mile walk of a major transit stop or high-quality transit corridor (plus two feet to align the roof pitch), or 18 feet on a lot with a multifamily, multistory home.

Attached ADUs may be 25 feet or the zone’s limit, whichever is lower, and never more than two stories. Setbacks follow the base zoning in front, with four feet on the side, street side and rear.

No additional setback is required to convert an existing structure, to build in the exact location of an existing structure, or to add a second story above an existing lawful structure.

Fullerton requires one parking space for an ADU unless it has no bedrooms, so a studio needs none. The space may be tandem on the driveway, with minimum dimensions of 9 feet by 19 feet.

The usual exemptions apply: half a mile from transit, historic districts, space within the main home or an accessory structure, no on-street permits offered, car share within one block, or an ADU submitted with a new home. Demolished or converted parking does not have to be replaced. JADUs need no additional parking.

Sprinklers, sale and rentals

Fire sprinklers are not required in an ADU if they are not required for the main home, and building an ADU does not trigger sprinklers in the existing home.

An ADU may not be sold or conveyed separately from the primary home, except as allowed by Government Code sections 66341 or 66342, so the unit goes with the house when you sell.

JADUs carry a recorded deed restriction: no separate sale, the size cap, no rental for less than 30 days, and owner occupancy in either the main home or the JADU. ADUs and JADUs may not be rented for less than 31 days under the ordinance’s rental provisions.

Fees and review

Section 15.17.100.C.2 exempts ADUs under 750 square feet from impact fees and charges larger ones proportionately to the main home. Public service and recreation impact fees must be paid before occupancy.

Applications are approved or denied ministerially within 60 days of a complete application, or 30 days if the plan is preapproved by the city or identical to a detached ADU approved within the current building-code cycle. If the city does not act within 60 days, the application is deemed approved.

What if my Fullerton ADU or garage conversion has no permit?

Fullerton’s ordinance has a dedicated section for units built before January 1, 2020.

Section 15.17.100.K says permits shall not be denied based on building standard violations or noncompliance with state law or the zoning code unless the city finds that correcting the violation is necessary to comply with Health and Safety Code section 17920.3 or the building is substandard.

Homeowners may obtain a confidential third-party code inspection before submitting a permit application. City inspectors may inspect for health and safety compliance, but the city will not penalize an applicant for having the unpermitted unit and will approve the permits needed to correct health and safety problems.

Impact fees, connection fees and capacity charges are not required for these units except when utility infrastructure is needed to comply with the health and safety statute.

And under the ordinance’s delay-of-enforcement provision, enforcement is delayed until January 1, 2030 once you file an application, if enforcement is not needed to protect health and safety. This mirrors state law at Government Code section 66311.7, added by AB 2533.

Ask the Planning Division at (714) 738-6559 what would apply to your property. See our Fullerton building permits guide and the Fullerton code enforcement guide.

How an unpermitted unit affects a sale

Sellers must disclose known unpermitted work on the Transfer Disclosure Statement. Buyers may ask you to legalize the unit, cut the price, give a credit or walk away, and lenders can be cautious about living space missing from city records.

Even with Fullerton’s friendlier legalization path, legalizing still takes time, inspections and money. A cash buyer can purchase the property with the unit unresolved and price the risk into the offer. See our guide to selling as-is with unpermitted work.

How to sell a house in Fullerton with an unpermitted ADU

1. Check city records. Confirm what the city shows as the legal unit count and square footage.
2. Consider a confidential inspection. Fullerton’s ordinance lets you get a third-party code inspection before applying.
3. Gather proof of age. Invoices, photos or utility records showing a pre-2020 build date matter.
4. Compare options. Legalize, sell with a credit, or sell as-is.
5. Disclose honestly. A cash offer does not change what you must disclose.

See selling a house as-is in Fullerton or our cash-offer process.

Questions about your unit? Call (424) 435-2326 or request a cash offer. No cost, no obligation.

Fullerton zoning and ADU FAQ

Did Fullerton update its ADU rules recently?

Yes. The City Council approved Ordinance No. 3343 on June 17, 2025, amending the zoning code for ADUs and JADUs.

How big can an ADU be in Fullerton?

Attached ADUs up to 850 square feet (studio or one bedroom) or 1,000 square feet (two or more bedrooms); detached ADUs up to 1,200 square feet; JADUs up to 500 square feet.

Does a Fullerton ADU need parking?

One space unless the ADU is a studio, with exemptions such as transit proximity and conversions.

Can I legalize an old unpermitted ADU in Fullerton?

The ordinance says permits for units built before January 1, 2020 shall not be denied for building standard violations unless needed for health and safety or the unit is substandard.

Does Fullerton let me get an inspection before applying?

Yes. The ordinance says homeowners may obtain a confidential third-party code inspection before submitting a permit application.

How long does Fullerton take to review an ADU?

Sixty days from a complete application, or 30 days with a pre-approved plan. The application is deemed approved if the city does not act in 60 days.

Can I sell a Fullerton house with an unpermitted ADU?

Yes, with disclosure. A cash buyer can purchase it as-is and price the risk into the offer.

Sources

• City of Fullerton: Accessory Dwelling Units (Granny Units)
• City of Fullerton: ADU Ordinance 3343 (June 17, 2025)
• California HCD: Accessory Dwelling Unit Handbook (March 2026)

This guide is general information, not legal advice. Rules change; confirm requirements with the City of Fullerton.