ADU Rules in Wentzville, Missouri

Wentzville is one of Missouri's fastest-growing cities, located in St. Charles County along the I-70 corridor, approximately 35 miles west of St. Louis. Wentzville has seen explosive population growth driven by affordable housing costs and proximity to St. Louis employment, growing from a small town to a city of more than 40,000 residents in recent decades. The city is characterized by newer planned residential subdivisions, active development, and many homeowners associations. ADU regulations are governed by the city's local Code of Ordinances. Missouri has enacted no statewide ADU preemption law.

Missouri State Law

Missouri has no statewide ADU preemption statute. Wentzville sets its own ADU rules through its local Code of Ordinances, zoning chapter.

Permitted ADU Types

Wentzville's zoning code addresses accessory dwelling units in residential zoning districts. Given the predominantly newer, single-family residential character of much of Wentzville, ADU standards reflect that context. Permitted types may include:

• Detached ADU: A freestanding structure on the same lot as the primary dwelling, typically in the rear yard.
• Attached ADU: An addition to the primary dwelling creating a separate, self-contained dwelling unit.
• Garage Conversion: Converting an existing garage into habitable ADU space.
• Interior or Lower Level Conversion: Adapting existing space within the primary structure, subject to building code compliance.

Permitted types and applicable standards vary by zoning district. Contact the Planning and Zoning Department to confirm what is allowed on your specific parcel.

Size, Setbacks, and Height

Dimensional standards are set by the applicable zoning district. General reference:

• Maximum size: Typically limited to a percentage of the primary dwelling's floor area or a fixed square footage cap per district.
• Setbacks: Rear and side yard setbacks for detached accessory structures are defined by district; commonly 5 feet or more from property lines in newer suburban districts.
• Height: Detached ADUs are generally limited to one story or a maximum height per district standards.
• Lot coverage: District-specific lot coverage maximums restrict total building area.

Always confirm current requirements with the Planning and Zoning Department before designing your project.

HOA Considerations — Important in Wentzville

Given Wentzville's rapid growth through planned residential development, a large proportion of properties are within subdivisions governed by homeowners associations. HOA CC&Rs are private legal agreements that operate independently of city zoning and may:

• Prohibit separate dwelling units or rental portions of a home.
• Restrict exterior additions, outbuildings, or garage modifications.
• Require HOA board approval for any structural changes.

City zoning approval does not override HOA restrictions. Always review your HOA documents and consult your HOA board before investing in ADU design or permit applications.

Flood Zone Considerations

Portions of Wentzville near local waterways — including Dardenne Creek and its tributaries — may be in FEMA-designated flood zones. Check FEMA's Flood Map Service Center (msc.fema.gov) for your property's flood zone status before planning any ADU construction.

Permit Process

1. Check zoning district: Confirm your property's zoning using the city's GIS portal.
2. Review HOA documents: Check CC&Rs for restrictions before proceeding.
3. Check flood zone status: Verify at FEMA's Flood Map Service Center.
4. Review Code of Ordinances: Identify ADU standards for your district.
5. Prepare plans: Work with a designer or architect to prepare required documents.
6. Submit building permit application: File with Wentzville's Building Division or Planning and Zoning Department.
7. Plan review: Staff reviews for zoning and building code compliance.
8. Permit issuance: Obtain permit before starting construction.
9. Inspections and Certificate of Occupancy: Complete required inspections; obtain CO before occupying.

Contact Information

City of Wentzville Planning and Zoning Department 5 W. Pearce Boulevard, Wentzville, MO 63385 Phone: (636) 327-5101 Website: wentzvillemo.org/planning

Disclaimer: Zoning regulations change frequently. Always verify current ADU rules directly with the City of Wentzville Planning and Zoning Department and your HOA before beginning any project. This page is for informational purposes only and does not constitute legal or zoning advice.