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.
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Frequently asked in St. Louis
What are the disadvantages of ADUs?
Potential disadvantages of ADUs can include increased utility bills for the main house and potential impacts on privacy or yard space. Some homeowners may also find managing a rental property to be time-consuming. It's important to consider how the ADU will integrate with your existing home and lifestyle. A professional can help you weigh these factors.
How much does an ADU cost in Missouri?
What are the rules for ADUs in Missouri?
While Missouri has general building codes, St. Louis has its own specific zoning ordinances and building regulations for accessory dwelling units. These often address lot coverage, setbacks, parking, and minimum unit size. It's essential to consult the current St. Louis building code for compliance. We can help you understand these rules.
Is an ADU allowed in St. Louis?
Yes, accessory dwelling units are permitted in St. Louis, but they must adhere to the city's zoning laws and building codes. These regulations typically cover aspects like the maximum size of the ADU, its placement on the property, and access to utilities. The city has specific guidelines for ADUs. A local expert can confirm your property's eligibility.
How do I find the best accessory dwelling unit in St. Louis?
What is the grant for ADUs in St. Louis?
Currently, there isn't a widespread statewide grant program for ADUs in Missouri. However, it's worth checking with the City of St. Louis or local utility companies for any potential incentives or energy efficiency rebates that might be available for accessory dwelling units. These can sometimes help offset costs. We can provide advice on exploring financial options.
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, Soulard, Central West End, Tower Grove, Benton Park — and every surrounding area.
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