Cost of 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
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 Costa Mesa
Are there prefab ADU options available in Costa Mesa?
Yes, prefab ADU options are available in Costa Mesa. Prefabricated or modular ADUs can offer faster construction times and potentially more predictable costs. These units are built off-site and then assembled on your property. The specialists can discuss if a prefab option is suitable for your needs and property.
How do I find accessory dwelling unit builders in Costa Mesa?
What is involved in accessory dwelling unit construction?
What is ADU housing?
ADU housing refers to accessory dwelling units, which are additional, independent living spaces on an existing residential property. This could be a detached structure in your backyard or an attached unit. It's a way to add valuable living space, whether for family members or as a rental. It maximizes your property's utility.
Are there 24-hour ADU services?
For new ADU construction or planned projects, '24-hour services' typically isn't applicable. However, if you have an urgent issue with an existing ADU, such as a plumbing emergency or structural concern, prompt service is crucial. Contacting experienced professionals quickly is key to resolving such issues. We can help you find the right support.
How do I get an ADU estimate?
Can I get a local ADU quote?
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 del Mar, South Coast Metro, Downtown Costa Mesa, Westside, Eastside — and every surrounding area.
Areas we serve
Browse by state, then city.
California (3)
All of California · Costa Mesa · Jurupa Valley · Santa Maria