Accessory dwelling unit cost — St. Louis, MO
Last updated: September 24, 2026
One part of building an accessory dwelling unit, or ADU, that often surprises St. Louis homeowners is the permitting process. It's more than just construction; it involves navigating city regulations. These units are secondary housing on your property, separate from your main home. They can be detached backyard cottages or attached additions. St. Louis, with a population of over 281,000, has many properties that can accommodate ADUs. Homeowners are exploring them for multi-generational living or rental income. We help demystify the permitting and construction process. Our goal is to make your ADU vision a reality in St. Louis. Let's discuss your project today.
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
Total costs are influenced by the complexity of your site, the square footage of the unit, and the specific utility upgrades needed to support a new home. Choosing between a prefab unit and a custom build also changes your bottom line. We provide exact pricing confirmed free on the call.
Frequently asked in St. Louis
What's the best ADU for my St. Louis property?
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What's involved in accessory dwelling unit construction in St. Louis?
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What are backyard accessory dwelling units 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, Tower Grove South, Soulard, Benton Park — and every surrounding area.
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