Cost of accessory dwelling unit — Ontario, CA

Looking for cost of accessory dwelling unit in Ontario, CA? Call AccessoryDwellingUnit Pros for a contact a provider — no obligation. Licensed adu builders serve Ontario and the surrounding area, and you'll get straight answers on timing and what affects the price.

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

The total investment for an ADU depends on several moving parts, including your property’s site conditions, the complexity of your site plan, and the high-end finishes you select. Whether you are building a detached cottage or converting a garage, costs vary based on utility connections and local labor rates. Exact pricing confirmed free on the call.

Frequently asked in Ontario

What are the disadvantages of ADUs?

Potential disadvantages include the initial construction costs and the time commitment. You'll also need to consider the impact on your existing yard space and privacy. While California has streamlined ADU laws, navigating the permitting process in Ontario can still be complex, though the pros we work with are experienced.

How much does an ADU cost in California?

What are the rules for ADUs in California?

Is an ADU allowed in Maryland?

This information pertains to Accessory Dwelling Units in Ontario, California. ADU regulations are highly localized and differ significantly by state and city. For Maryland, you need to consult Maryland-specific resources and local building authorities.

What are the rules for ADU in California?

California has been a leader in ADU legislation, aiming to simplify the process statewide. However, local cities within California can still have specific requirements. These rules are specific to California and do not directly apply to ADU development in Ontario, California, where local ordinances are paramount.

Also serving nearby: Chino · Rancho Cucamonga · Jurupa Valley · Pomona · Fontana

All cities in California →

More on this: HUD ADU resources — ADU policy and financing research.

Service area details

182,457residents

3,650per sq mile

4ZIP codes served

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: Central Ontario, Eastvale, Rancho Cucamonga, Chino Hills, Jurupa Valley — and every surrounding area.