ADU Regulations in Ontario, California
Everything you need to know about building an ADU in Ontario — size limits, setbacks, permits, and costs.
How many ADUs are allowed in Ontario?
- → 1 Detached ADU (up to 1,200 sq ft)
- → 1 Attached ADU
- → 1 Junior ADU / JADU (up to 500 sq ft)
- → Up to 8 detached ADUs
- → Interior conversions up to 25% of existing units
All California cities must follow state-law minimums. Ontario follows California AB 68 and subsequent ADU laws.
Ontario ADU rules & limits.
| ADUs Allowed | Up to 3 units on a single-family lot (primary home + 1 ADU + 1 JADU); up to 8 detached ADUs on multifamily lots |
|---|---|
| Max ADU Size | 1,200 sq ft |
| Setbacks | 4 ft side & rear (CA state baseline) |
| Height | 16 ft detached, 18 ft permitted near transit corridors |
| Parking | Not required in most cases; no replacement parking for garage conversions |
| JADU Allowed | Yes — up to 500 sq ft; owner-occupancy required if JADU is present |
| Impact Fees | Waived under 750 sq ft (state law) |
| Permit Timeline | 60 days maximum (state-mandated review window) |
Ontario follows the California state ADU baseline with expanded height allowance near transit. The Ontario International Airport flight paths affect some neighborhoods — noise insulation requirements may apply on parcels under the approach corridor.
Contact: Ontario Planning: (909) 395-2036
What could your Ontario ADU earn?
Rental estimates based on current Inland Empire market rates. Actual rents vary by condition, amenities, and local demand.
Four paths to an ADU in Ontario.
From idea to reveal.
Free Feasibility Consultation
We walk your lot, check setbacks and lot coverage, and confirm what your jurisdiction will approve.
Design & Engineering
Floor plan, elevations, structural calcs, and Title 24 energy compliance — drawn for your specific lot.
Permit Submission & Approval
We submit to your city or county, manage plan-check corrections, and pay the permit fees.
Construction
Same Construction Station crew handles foundation, framing, MEP, drywall, and finish — start to keys.
Final Inspection & Move-In Ready
Final city inspection, certificate of occupancy where applicable, and two-year workmanship warranty.
Why build an ADU in Ontario.
Ontario's economic gravity is unmatched in the western Inland Empire. Ontario International Airport employs over 7,000 people directly, the surrounding logistics corridor employs tens of thousands more, and Ontario Mills, Toyota Arena, and the Convention Center generate continuous workforce demand. Long-term rental demand for ADUs in the 600–1,000 sq ft range is exceptionally strong, and the city's central location within the Inland Empire — equidistant from Riverside, San Bernardino, and Los Angeles County — keeps tenant pool diversity high. The 18 ft transit-corridor height allowance is particularly useful in the Ontario Center and Holt Boulevard neighborhoods. Older Ontario neighborhoods near Euclid Avenue have substantial detached garages from the 1920s and 1930s that make excellent garage-conversion candidates with character-driven finishes. Construction Station pulls Ontario permits regularly.
Ready to build an ADU in Ontario?
We’ll walk your lot, confirm what Ontario will allow, and ballpark cost before you commit to anything.
Ontario ADU questions, answered.
How much does an ADU cost in Ontario?
How long does it take to get an ADU permit in Ontario?
Can I rent my ADU in Ontario?
Do I need owner-occupancy for an ADU in Ontario?
Does Construction Station build ADUs in Ontario?
ADU regulations change frequently. Always verify current requirements with the Ontario Planning Department at (909) 395-2036. This page was last updated May 2026.