What does accessory dwelling unit mean — 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

An accessory dwelling unit is simply a secondary, self-contained living space located on the same lot as a primary house. It includes its own kitchen, bathroom, and sleeping area. People build them to increase property value, house family members, or create a source of passive income. If you are looking to maximize your land use, this is the definition you need.

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, South Coast Metro, The Lower Bay, The Westside, The Eastside — and every surrounding area.