Detached accessory dwelling unit — Costa Mesa, 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

A detached ADU is a standalone building separate from your main house, like a cottage or a converted garage. You choose this style if you want maximum privacy for your tenants or family members. Because it requires its own foundation and utility lines, it is a significant construction project. Exact pricing confirmed free on the call.

Frequently asked in Costa Mesa

Also serving nearby: Santa Ana · Huntington Beach · Westminster · Irvine · Garden Grove

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

Service area details

Serving all of Costa Mesa — population 108,354; about 6,855 residents per square mile across 15.8 sq mi. ZIP codes covered include 92626, 92627, 92628.

Neighborhoods served in Costa Mesa: Mesa del Mar, The Westside, South Coast Metro, Fairview Shores — and every surrounding area.