Everything homeowners need to know about building an accessory dwelling unit in Fullerton, California - size limits, setbacks, permits, and how the city's standards fit within California's statewide ADU law.
Last verified: August 2026
7/10 · ADU-friendly, with some friction
1,200 sq ft*
Max ADU size
16 ft*
Max height
Not required*
Owner-occupancy
By-right
Permit type
This page summarizes Fullerton Municipal Code Title 15, Section 15.17.100 (Accessory and Junior Accessory Dwelling Units) plus California's statewide ADU law for general reference - it is not legal advice. Regulations change; always confirm current requirements with the City of Fullerton Planning Division before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build)
Up to 1,200 sq ft under the city's local standard, well above the state default caps of 850 sq ft (studio/1-bedroom) and 1,000 sq ft (2+ bedrooms)
Generally 16 ft for a single-story detached ADU, with additional allowances near transit and on qualifying multi-family lots under state law
One detached ADU permitted per single-family lot
Attached (addition or living-area conversion)
Up to 50% of the primary dwelling's floor area, or 1,200 sq ft, whichever is less
Limited by the height allowed for the primary structure in the underlying zone
Must be attached to or created within the existing home
Junior ADU (JADU)
Up to 500 sq ft
Within the existing walls of the home
Must be contained entirely within an existing or proposed single-family residence
Allowed zoning districts
Single-family and multi-family residential zones citywide, on any lot with a proposed or existing primary dwelling. Confirm your parcel's zoning with the Planning Division before designing.
Additional standards
Setbacks, parking & other rules
Setbacks
Minimum 4 ft side and rear yard setbacks for new-construction ADUs; front and street-side setbacks generally follow the underlying zoning district
Parking
Follows California's default framework: generally one space per ADU or bedroom, waived when the ADU is within a half mile of transit, replaces a converted garage or carport, or falls under another state-law exemption
Units per lot
1 ADU plus 1 JADU on a single-family lot
Owner-occupancy
Not required for a standard ADU, per California's AB 976 (effective 2024), which permanently bars cities from requiring owner-occupancy for ADUs. Still required for a lot with a JADU
Rental terms
ADU and JADU rentals must run longer than 30 days; short-term/vacation rentals are not permitted
Building code
Must meet current California Residential Code and California Building Code standards for dwelling units
Impact fees
Waived for ADUs under 750 sq ft, as required statewide; charged proportionately to the primary home's floor area above that size
Ordinance history
How Fullerton's ADU rules got here
2020Modern ADU ordinance adopted. Ordinance No. 3280, approved by the City Council on April 7, 2020, implemented the major 2019-2020 wave of state ADU legislation into Fullerton Municipal Code Title 15.
2021Housing Element deadline missed. Fullerton failed to adopt a compliant 2021-2029 Housing Element by the October 15, 2021 statutory deadline, and did not act for over a year after HCD found its draft substantially noncompliant.
2024State settlement over Housing Element law. California's Attorney General announced a settlement with the city on January 18, 2024, requiring Fullerton to adopt a compliant Housing Element and modernize its zoning to accommodate roughly 13,209 housing units, including more than 5,000 low- and very-low-income units.
2025ADU ordinance overhauled. The City Council approved Ordinance No. 3343 on June 17, 2025, updating Title 15's ADU and JADU standards to align with the current wave of state ADU law.
Worth knowing: Fullerton's individual ADU zoning standards are relatively generous on paper, including a local size cap well above the state default. But the city's broader, well-documented struggle to comply with state housing law, including a formal Attorney General settlement, is worth keeping in mind when weighing how smoothly city processes tend to run.
Permit process
How Fullerton ADU permitting works
1
Pre-application check
Confirm your zoning district and which ADU category applies with the Planning Division at (714) 738-6559 before you design.
2
Prepare your plan set
You'll need a site plan, floor plans and elevations for the ADU, and, for attached or conversion projects, floor plans of the existing home to verify the size calculation.
3
Submit your application
File your ADU application and required materials per the city's Applications & Fees requirements; digital submittal is standard.
4
Ministerial review (up to 60 days)
The city reviews for zoning and code compliance without a discretionary hearing and must act within 60 days of a complete submittal.
5
Building permit & inspections
Once your ADU application is approved, pull your building permit through Building & Safety and schedule the standard framing, plumbing, electrical, and final inspections.
6
Record the deed restriction (JADU only)
Before occupancy, a JADU needs a recorded deed restriction prohibiting separate sale from the primary home; standard ADUs do not require one.
Fees and timelines are approximate - confirm current figures with the Planning Division before applying.
Budgeting
What it costs to build an ADU in Fullerton
Garage conversion
Roughly $70,000-$180,000, generally the least expensive path since the shell already exists
Attached / interior conversion
Roughly $100,000-$220,000, depending on existing layout and utility access
New detached ADU
Roughly $150,000-$340,000 or more for a code-compliant, fully finished freestanding unit, with larger 1,200 sq ft units trending toward the higher end
Impact fees
Waived for ADUs under 750 sq ft; charged proportionately to the primary home's floor area above that threshold
Planning & plan-check fees
Vary by project size and scope; confirm the current fee schedule with the Planning Division
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and whether utilities need to be extended.
Before you apply
Tips for a smooth approval
Confirm the current size cap before you design. Fullerton's ordinance was substantially rewritten in June 2025, so double-check the maximum square footage and height that applies to your project with Planning rather than relying on older guides.
Get your setback measurements right the first time. The 4 ft side and rear minimums apply only to new-construction square footage; conversions of existing structures are typically exempt.
Ask about parking exemptions before assuming you need a space. Transit proximity and garage-conversion exemptions frequently eliminate the requirement entirely.
Budget for both planning and building fees. They're assessed separately, and it's easy to price only one when comparing contractor quotes.
Get city commitments in writing. Given the city's history of housing-law compliance issues, it's worth documenting any zoning determinations or verbal guidance you receive during pre-application conversations.
FAQ
Common questions
Do I need to live on the property to build an ADU in Fullerton?
No, not for a standard ADU. California's AB 976 permanently eliminated owner-occupancy mandates for ADUs statewide starting in 2024. Owner-occupancy is still required if you build a Junior ADU (JADU) instead.
How many ADUs can I build on one lot?
A single-family lot generally allows one ADU plus one JADU.
Do I need extra parking for an ADU?
Often not. Parking is commonly waived when the ADU is within a half mile of transit or converts existing space such as a garage; otherwise expect to provide roughly one space.
How long does the permit process take?
The city must act on a complete ADU application within 60 days, without a public hearing. Confirm current timelines with the Planning Division, since total time from design through permit issuance runs longer once plan preparation is included.
What's the maximum size for a detached ADU?
Up to 1,200 sq ft under the city's local standard, which is more generous than the state default caps of 850 sq ft (studio/1-bedroom) and 1,000 sq ft (2+ bedrooms) used in many other cities.
How much does an ADU cost to build in Fullerton?
Garage conversions tend to run roughly $70,000-$180,000, attached or interior conversions $100,000-$220,000, and new detached units $150,000-$340,000 or more, based on local contractor estimates and regional reporting - not counting permit and impact fees where they apply.
Has Fullerton had housing-law compliance problems?
Yes, though it centered on the city's overall Housing Element rather than the ADU ordinance specifically. Fullerton missed its 2021-2029 Housing Element deadline, and California's Attorney General reached a settlement with the city in January 2024 requiring it to adopt a compliant plan and modernize its zoning for future housing. The city's own ADU-specific size and setback standards are comparatively generous.
Can I rent my ADU out on Airbnb or a short-term rental platform?
No. Fullerton requires ADU and JADU rentals to be for terms longer than 30 days, which rules out short-term or vacation-rental use.
Can I sell my ADU separately from the main house?
Generally no. State law allows ADUs to be rented separately from the primary residence but not sold or conveyed separately, aside from a narrow exception for units built by a qualified nonprofit for income-qualified buyers.
