Accessory dwelling unit services — Ontario, CA

Last updated: September 24, 2026

What affects the price

Building an ADU involves several moving parts that shape your total investment. The final figure depends heavily on whether you choose a prefab unit or a custom build from the ground up. Site conditions are another major factor; if your property requires extensive grading, utility trenching, or foundation work, costs will climb. You also have to consider your choice of finishes, like high-end appliances or custom cabinetry. Navigating local permit fees and impact assessments also adds to the total.

About this service

These services cover the end-to-end process of adding a secondary home to your property. This includes initial zoning checks, architectural design, permit filing, and final construction. You need these services when you want to create a separate living space for family, guests, or as a rental unit, but don’t want to manage the complex legal and structural requirements on your own.

Frequently asked in Ontario

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

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: Creekside, Museum Square, Downtown Ontario, North Ontario, South Ontario — and every surrounding area.