Accessory dwelling unit construction cost — Urban Honolulu, HI

Last updated: September 24, 2026

What affects the price

Building an ADU is a custom project, so costs vary based on your specific choices. Site conditions are the biggest factor; if your land requires significant grading, utility extensions, or foundation work, those expenses add up quickly. Choosing high-end finishes, custom cabinetry, or complex roof lines will also push the budget higher compared to a standard design. Prefabricated units often offer predictable costs, while custom site-built structures allow for more flexibility but can be harder to estimate upfront. Exact pricing confirmed free on the call.

About this service

Building costs vary based on the size of the unit, the quality of finishes, the complexity of the site foundation, and utility connections. You should consider these expenses when budgeting for a long-term property investment or home expansion. Exact pricing confirmed free on the call.

Frequently asked in Urban Honolulu

Also serving nearby: San Francisco · Daly City · San Mateo · Salinas · Santa Maria

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

Service area details

Serving all of Urban Honolulu — population 341,778; about 5,637 residents per square mile across 60.6 sq mi.

Neighborhoods served in Urban Honolulu: Diamond Head, Kaimuki, Kapahulu, Manoa, Makiki, Nu'uanu — and every surrounding area.