Accessory dwelling unit construction cost — Fontana, CA

Last updated: September 24, 2026

What affects the price

Building an ADU involves variables that shift your total investment. The footprint size and complexity of the architectural design are primary factors. Are you planning a detached unit that requires new utility trenching, or is this a garage conversion that uses existing plumbing? Site accessibility, soil conditions, and your choice of finishes—like luxury flooring versus standard options—also play significant roles. Permitting fees vary widely depending on your local municipality and current zoning requirements. Exact pricing confirmed free on the call.

About this service

The amount you spend depends on the size of the unit, whether you are building from scratch or converting an existing structure, and the quality of your finish materials. Foundations, utility connections, and local labor rates also play a significant role. We provide exact pricing confirmed free on the call.

Frequently asked in Fontana

Also serving nearby: Rialto · Rancho Cucamonga · Jurupa Valley · Ontario · San Bernardino

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

Service area details

Serving all of Fontana — population 215,465; about 4,978 residents per square mile across 43.3 sq mi. ZIP codes covered include 92331, 92334, 92335, 92336, 92337.

Neighborhoods served in Fontana: North Fontana, South Fontana, East Fontana, West Fontana, Hunter's Ridge, Cimmaron — and every surrounding area.