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Accessory dwelling unit permit cost — St. Louis, MO

Looking for accessory dwelling unit permit cost in St. Louis, MO? Call AccessoryDwellingUnit Services for a contact a provider — no obligation. Licensed adu builders serve St. Louis and the surrounding area, and you'll get straight answers on timing and what affects the price.

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.

Frequently asked in St. Louis

What are the disadvantages of ADUs?

Potential disadvantages include the initial construction cost and the possibility of higher utility bills. Some homeowners might also face challenges with zoning laws or neighborhood opposition. However, the long-term benefits, such as increased property value and rental income, are often substantial. We can help you explore these.

How much does an ADU cost in Missouri?
What are the rules for ADUs in Missouri?

Missouri has state ADU guidelines, but individual cities like St. Louis have their own specific ordinances. These rules often dictate things like setbacks, lot coverage, and the maximum size of the ADU. Understanding these local regulations is crucial for a successful permitting process. We can help you find professionals who know St. Louis's rules.

Is an ADU allowed in St. Louis?

Yes, accessory dwelling units are generally allowed in St. Louis, provided they meet the city's zoning and building codes. These regulations often cover aspects like the ADU's size, location on the lot, and its integration with the main house. It's always best to consult with local experts familiar with St. Louis's specific requirements. Let us help you find them.

What is the permit cost for an ADU?

Permit costs for an ADU in St. Louis can fluctuate based on the project's scope and the city's fee structure. These fees cover the review of your plans and subsequent inspections to ensure compliance. A professional who regularly works on ADU projects in St. Louis can provide a more accurate estimation of these costs. Call us for assistance.

Can I add a second ADU on my property?

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

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

Service area details

281,754residents
4,565per sq mile
—ZIP codes served

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, Benton Park, Soulard — and every surrounding area.

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