Modular 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 modular unit is built in a factory and then transported to your property to be finished on a foundation. You should consider this if you want a faster construction timeline with less disruption to your daily life. It is an efficient way to add high-quality space to your lot.
Frequently asked in Costa Mesa
What should I have ready before my ADU appointment in Costa Mesa?
What is the cost to build an accessory dwelling unit in Costa Mesa?
What makes an ADU the 'best' option for my property in Costa Mesa?
What are the different types of ADU housing available in Costa Mesa?
What are the options for accessory dwelling unit financing in Costa Mesa?
What are accessory dwelling units (ADUs)?
What is the accessory dwelling unit permit cost in Costa Mesa?
Also serving nearby: Santa Ana · Huntington Beach · Westminster · Irvine · Garden Grove
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 Verde, South Coast Metro, The Mesa, Westside Costa Mesa — and every surrounding area.
Areas we serve
Browse by state, then city.
California (3)
All of California · Costa Mesa · Jurupa Valley · Santa Maria