Accessory dwelling unit permit cost — Ontario, CA
Last updated: September 24, 2026
What affects the price
Building an ADU is a custom project, so costs vary based on your specific choices. Site conditions are the biggest factor; if your land requires significant grading, utility extensions, or foundation work, those expenses add up quickly. Choosing high-end finishes, custom cabinetry, or complex roof lines will also push the budget higher compared to a standard design. Prefabricated units often offer predictable costs, while custom site-built structures allow for more flexibility but can be harder to estimate upfront. Exact pricing confirmed free on the call.
About this service
Permit fees are paid to your local municipality and fluctuate based on the specific city or county where your property is located. These costs cover plan reviews, impact fees, and safety inspections required to make your new space legal and compliant. Because every jurisdiction has a different fee structure, the final amount depends on your specific town’s regulations. We help you estimate these during the planning phase. Exact pricing confirmed free on the call.
Frequently asked in Ontario
What are the disadvantages of ADUs?
Potential disadvantages include the upfront construction costs and the complexities of California's ADU laws, which can be intricate for Ontario. You may also face challenges with utility connections and ensuring your ADU complies with all zoning requirements. A local pro is essential for navigating these hurdles.
How much does an ADU cost in California?
The cost of an ADU in California varies widely based on size, design, and site preparation in Ontario. Key cost drivers include permit fees, architectural plans, foundation work, and the quality of finishes. Professionals can provide a detailed quote after assessing your property and specific ADU plans.
What are the rules for ADUs in California?
California has statewide ADU laws that cities must follow, but local ordinances in Ontario can add specific requirements regarding setbacks, parking, and lot coverage. It's vital to work with a pro who understands both the state mandates and the precise regulations for San Bernardino County to ensure compliance.
What are the disadvantages of ADUs?
Potential disadvantages include the upfront construction costs and the complexities of California's ADU laws, which can be intricate for Ontario. You may also face challenges with utility connections and ensuring your ADU complies with all zoning requirements. A local pro is essential for navigating these hurdles.
How much does an ADU cost in California?
The cost of an ADU in California varies widely based on size, design, and site preparation in Ontario. Key cost drivers include permit fees, architectural plans, foundation work, and the quality of finishes. Professionals can provide a detailed quote after assessing your property and specific ADU plans.
What are the rules for ADUs in California?
California has statewide ADU laws that cities must follow, but local ordinances in Ontario can add specific requirements regarding setbacks, parking, and lot coverage. It's vital to work with a pro who understands both the state mandates and the precise regulations for San Bernardino County to ensure compliance.
Also serving nearby: Chino · Rancho Cucamonga · Jurupa Valley · Pomona · Fontana
More on this: HUD ADU resources — ADU policy and financing research.
Service area details
Serving all of Ontario — population 182,457; about 3,650 residents per square mile across 50.0 sq mi. ZIP codes covered include 91758, 91761, 91762, 91764.
Neighborhoods served in Ontario: Downtown Ontario, Central Ontario, West Ontario, East Ontario, South Ontario — and every surrounding area.
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