Cost of accessory dwelling unit — Modesto, 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

Building an ADU involves several variables that shift the total investment. Your site conditions, the type of foundation, and the quality of finishes you choose will dictate whether you land on the lower or higher end of the spectrum. Because every lot is unique, we provide a breakdown of your specific project requirements to ensure full transparency. Exact pricing confirmed free on the call.

Frequently asked in Modesto

Also serving nearby: Manteca · Tracy · Stockton · Merced · Antioch

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

Service area details

Serving all of Modesto — population 218,915; about 5,049 residents per square mile across 43.4 sq mi. ZIP codes covered include 95350, 95351, 95352, 95353, 95354, 95355, 95356, 95357.

Neighborhoods served in Modesto: Downtown Modesto, Salida, Ceres, Keyes, Empire — and every surrounding area.