Everything homeowners need to know about building an accessory dwelling unit in Fontana - size limits, setbacks, permits, and the four ADU pathways the city lays out for single-family lots.
Last verified: August 2026
9/10 · Very ADU-friendly
1,200 sq ft*
Max ADU size
16-18 ft
Max height
Not required*
Owner-occupancy
By-right
Permit type
This page summarizes Fontana Municipal Code Section 30-467 (Accessory Dwelling Units and Junior Accessory Dwelling Units) and the city's official ADU Information Sheet for general reference only, and it is not legal advice. Regulations change; always confirm current requirements with the Fontana Planning Department 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
Junior ADU (JADU)
500 sq ft
Within the existing home
Converted from existing living space or an attached garage; needs its own kitchen and a bathroom, shared or separate
Class 1 - detached, state-regulated
800 sq ft
16 ft
The guaranteed by-right floor: no parking and no architectural design review required
New construction, attached
50% of the primary home's floor area, or 850 sq ft (studio/1-bed) / 1,000 sq ft (2+ beds), whichever is larger
Generally matches the primary home
1 parking space typically required, with exemptions
Class 2 - detached, locally regulated
1,200 sq ft
16-18 ft
1 parking space typically required; must be architecturally compatible with the primary home
Allowed zoning districts & unit combinations
ADUs are permitted in all residential and mixed-use zones that allow residential uses. A single-family lot can typically combine one JADU, one Class 1 ADU, and one conversion ADU. Multifamily lots can add detached ADUs up to eight units (capped at the number of existing primary units) or converted ADUs up to 25% of the existing unit count. Confirm your parcel's zoning with the Planning Department.
Additional standards
Setbacks, parking & other rules
Setbacks
4 ft side and rear yard for new construction; an 18 ft front setback applies outside the guaranteed Class 1 pathway, which needs only the 4 ft side/rear setbacks.
Parking
Not required for JADUs, Class 1 ADUs (up to 800 sq ft), or conversions. Generally 1 space per ADU for attached and Class 2 detached units, with exemptions near transit and in other state-defined scenarios (FMC §30-467).
Units per lot
Up to three on a single-family lot (1 JADU + 1 Class 1 ADU + 1 conversion ADU); more on qualifying multifamily lots.
Owner-occupancy
Not required for ADUs. A JADU only requires owner-occupancy when its bathroom is shared with the main house.
Building code
Must meet current California Building/Residential Code standards. Class 2 detached ADUs must be architecturally compatible with the primary dwelling; Class 1 ADUs have no design-review requirement.
Rental restriction
A 30-day minimum rental term applies to both ADUs and JADUs - short-term/Airbnb-style rentals aren't permitted.
Impact fees
Waived for ADUs and JADUs of 750 sq ft or less; building permit and plan-check fees still apply to all units.
Ordinance history
How Fontana's ADU rules got here
2017Statewide by-right ADU law takes effect. California Government Code §65852.2 begins requiring cities, including Fontana, to approve qualifying ADUs ministerially, without discretionary review.
2020State reforms tighten local authority. AB 68, AB 881, and AB 587 narrow what cities can restrict, and Fontana updates its Municipal Code accordingly.
Nov 2024Urgency ordinance adopted. Fontana passes an urgency measure to keep Section 30-467 aligned with new state requirements set to take effect January 1, 2025.
Jan 2025AB 2533 and SB 1211 take effect. SB 1211 raises the multifamily-lot detached ADU cap statewide from two to as many as eight units.
Apr 8, 2025Permanent Ordinance No. 1966 adopted (4-0). The City Council formally updates FMC §30-467: raises the multifamily detached-ADU cap to eight, drops mandatory parking replacement, and extends the unpermitted-ADU legalization cutoff from 2018 to 2020.
2026Further alignment with 2025 state laws. The Planning Commission moves to update the ordinance for SB 543, AB 1154, and AB 462 - adding a faster 15-day review for some applications, a 500 sq ft no-parking threshold, and extending the 30-day minimum rental term to JADUs. The city's ADU Information Sheet was updated in March 2026.
Worth knowing: Fontana has kept its ADU ordinance unusually current, revising it twice in the past two years to track fast-moving state law. That's a good sign for homeowners, but it also means older third-party guides may already be out of date - always check the city's current ADU Information Sheet before finalizing plans.
Permit process
How Fontana ADU permitting works
1
Confirm your zoning & ADU class
Call Planning at (909) 350-6718 or email planning@fontanaca.gov, or review the city's ADU Information Sheet, to see whether your project fits the JADU, Class 1, attached, or Class 2 pathway.
2
Pick a design
Choose one of the city's AB 1332 pre-approved plans (Morning Glory, 462 sq ft; Carnation, 738 sq ft; or Sunflower, 1,143 sq ft, all through Tang Structural Engineers) or hire your own designer.
3
Assemble your submittal
Prepare a site plan, floor plans and elevations, and structural/energy documentation. Class 2 units also need to demonstrate architectural compatibility with the primary home.
4
Submit for review
Qualifying by-right applications must be decided within 60 days; some categories added under 2025 state law get a faster 15-day review. Development Services/Building & Safety can be reached at (909) 350-7600.
5
Pull your building permit & build
Begin construction once your permit is issued, and schedule the standard framing, plumbing, electrical, and final inspections.
6
Final inspection
Complete final inspections before renting the unit out. Remember the 30-day minimum rental term applies from day one.
Fees and timelines are approximate - confirm current figures with the Planning Department before you apply.
Budgeting
What it costs to build an ADU in Fontana
Garage conversion
Roughly $60,000-$150,000, the least expensive path since the shell already exists
New detached ADU
Roughly $130,000-$280,000 depending on size (Class 1 units capped at 800 sq ft tend to land toward the lower end, Class 2 units up to 1,200 sq ft toward the higher end)
Pre-approved plan savings
Choosing one of the three free AB 1332 designs can reduce design costs and shorten plan review versus a fully custom project
Impact fees
Waived for units 750 sq ft or smaller under Gov. Code §66311.5; building permit and plan-check fees still apply to every unit
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and whether you need a parking space added for an attached or Class 2 unit.
Before you apply
Tips for a smooth approval
Match your project to the right class. Class 1 (800 sq ft, no parking, no design review) is the fastest path; Class 2 (up to 1,200 sq ft) needs a parking space and architectural compatibility.
Use a pre-approved plan if one fits. Morning Glory, Carnation, and Sunflower are already vetted for code compliance, which can meaningfully shorten your review.
Watch the parking trigger. Most projects over 800 sq ft and all attached ADUs need one parking space unless a state-law exemption applies - confirm before you finalize your site plan.
Plan your rental strategy up front. Both ADUs and JADUs carry a 30-day minimum rental term, so short-term rental income isn't an option here.
Ask about the 750 sq ft fee waiver. Impact fees disappear below that threshold, which is worth weighing if you're deciding between a slightly smaller or larger unit.
FAQ
Common questions
Do I need to live on the property to build an ADU in Fontana?
No, for standard ADUs. A JADU only requires owner-occupancy when its bathroom is shared with the main house; a JADU with its own separate bathroom does not require it.
How many ADUs can I build on one lot?
Up to three on a single-family lot: one JADU, one Class 1 detached ADU, and one conversion ADU. Lots with an existing multifamily dwelling can add up to eight detached ADUs.
Do I need parking for my ADU?
Not for JADUs, Class 1 ADUs (up to 800 sq ft), or conversions. Attached ADUs and Class 2 detached ADUs generally need one parking space, though state-law exemptions can apply.
How long does the permit process take?
State law caps ministerial review at 60 days. Some categories covered by 2025 state legislation are entitled to a faster 15-day review.
What's the maximum size for a detached ADU?
800 sq ft is guaranteed under the Class 1 pathway. Under the city's Class 2 standard, detached ADUs can reach up to 1,200 sq ft.
How much does an ADU cost to build in Fontana?
Garage conversions tend to run roughly $60,000-$150,000, and new detached units roughly $130,000-$280,000 depending on size, based on local contractor estimates and regional reporting - not counting impact fees or parking-space costs where they apply.
Does Fontana offer pre-approved ADU plans?
Yes. Three AB 1332 pre-approved designs are available through Tang Structural Engineers - Morning Glory (462 sq ft), Carnation (738 sq ft), and Sunflower (1,143 sq ft) - which can shorten plan review compared to a custom design.
Can I rent my ADU out on Airbnb or a short-term rental platform?
No. Fontana requires a minimum 30-day rental term for both ADUs and JADUs, so short-term/Airbnb-style rentals aren't permitted.
Has Fontana's ADU ordinance changed recently?
Yes. The City Council adopted permanent Ordinance No. 1966 in April 2025, and the Planning Commission moved to update the ordinance again in 2026 to track new 2025 state ADU laws. Confirm the current standards with Planning before designing.
