Cost of accessory dwelling unit — 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

Building an ADU involves several variables that shift your final total, such as the size of the unit, whether you choose a detached structure or a garage conversion, and the complexity of your site’s plumbing and electrical needs. We help you navigate these choices to keep your project on track. Exact pricing confirmed free on the call.

Frequently asked in St. Louis

Also serving nearby: O Fallon · Springfield · Columbia · Champaign · Peoria

All cities in Missouri →

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, Benton Park — and every surrounding area.