Accessory dwelling unit construction cost — St. Louis, MO
Last updated: September 24, 2026
What affects the price
Building an ADU involves variables that shift your total investment. The footprint size and complexity of the architectural design are primary factors. Are you planning a detached unit that requires new utility trenching, or is this a garage conversion that uses existing plumbing? Site accessibility, soil conditions, and your choice of finishes—like luxury flooring versus standard options—also play significant roles. Permitting fees vary widely depending on your local municipality and current zoning requirements. Exact pricing confirmed free on the call.
About this service
The amount you spend depends on the size of the unit, whether you are building from scratch or converting an existing structure, and the quality of your finish materials. Foundations, utility connections, and local labor rates also play a significant role. We provide exact pricing confirmed free on the call.
Frequently asked in St. Louis
Where can I find ADU contractors in St. Louis?
What is the cost of an ADU in St. Louis?
What are ADU construction services in St. Louis?
Are there options for prefab ADUs in St. Louis?
What are homes with in-law suites like in St. Louis?
What is the best ADU for my property in St. Louis?
What ADU companies are in St. Louis?
Also serving nearby: O Fallon · Springfield · Columbia · Champaign · Peoria
More on this: HUD ADU resources — ADU policy and financing research.
Service area details
Serving all of St. Louis — population 281,754; about 4,565 residents per square mile across 61.7 sq mi.
Neighborhoods served in St. Louis: The Hill, Central West End, Soulard, Tower Grove South, CWE — and every surrounding area.
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