ADU Rules in Chesterfield, Missouri

Chesterfield is an affluent city in western St. Louis County, incorporated in 1988. Home to approximately 47,000 residents, Chesterfield is known for its high-quality residential neighborhoods, strong commercial corridor along Chesterfield Valley, and significant post-flood redevelopment history. 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. Chesterfield sets its own ADU rules through its local Code of Ordinances, zoning chapter.

The 1993 Great Flood and Chesterfield Valley — Critical Context

On July 30, 1993, during the Great Flood of the Missouri River, the levees protecting Chesterfield Valley failed, inundating the valley — which was then largely agricultural — under more than 15 feet of water. The flooding devastated the valley and prompted a major rethinking of land use. In subsequent years, Chesterfield Valley was redeveloped into a major commercial and mixed-use district, protected by improved and federally certified levees.

For ADU projects in Chesterfield:

• Properties in Chesterfield Valley or near the Missouri River may still carry FEMA flood zone designations despite levee improvements.
• FEMA's determination of levee-protected status affects flood insurance requirements and floodplain development restrictions.
• Always check FEMA's Flood Map Service Center (msc.fema.gov) and confirm current levee certification status with the city or FEMA before planning any ADU in low-lying areas.
• Properties in FEMA Special Flood Hazard Areas must meet city floodplain ordinance and FEMA NFIP elevation requirements.

Permitted ADU Types

Chesterfield's zoning code addresses accessory dwelling units in residential zoning districts. 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 or internal portion of the primary dwelling creating a separate unit.
• Garage Conversion: Converting an existing garage into habitable ADU space.
• Interior/Lower Level Conversion: Adapting existing finished or unfinished lower level space within the primary structure.

Permitted types and standards vary by zoning district. Confirm with Planning and Development Services.

Size, Setbacks, and Height

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

• Maximum size: Typically capped at a percentage of the primary dwelling's floor area or a fixed square footage limit.
• Setbacks: Rear and side setbacks for detached accessory structures are district-specific; commonly 5 feet or more.
• Height: Detached ADUs are generally limited to one story or a maximum accessory structure height per district.
• Lot coverage: Maximum lot coverage limits apply.

Always verify current standards with Planning and Development Services.

HOA Considerations

Chesterfield has many residential subdivisions governed by homeowners associations (HOAs). HOA CC&Rs may restrict or prohibit ADUs, detached accessory structures, or short-term rentals independently of city zoning. City zoning approval does not override HOA restrictions. Review your HOA documents and consult your HOA board before investing in ADU plans.

Permit Process

1. Check zoning district: Confirm your property's zoning using Chesterfield's online GIS portal.
2. Verify flood zone status: Check FEMA's Flood Map Service Center; confirm levee certification status if in or near Chesterfield Valley.
3. Review HOA documents: Check CC&Rs for any restrictions.
4. Review Code of Ordinances: Identify ADU standards for your district.
5. Pre-application consultation: Contact Planning and Development Services to discuss your project.
6. Prepare plans: Engage an architect or designer to prepare required documents.
7. Submit building permit application: File with Chesterfield's Building Division.
8. Plan review: Staff reviews for zoning, building code, and floodplain compliance.
9. Permit issuance: Obtain permit before starting construction.
10. Inspections and Certificate of Occupancy: Complete required inspections; obtain CO before occupying.

Contact Information

City of Chesterfield Planning and Development Services 690 Chesterfield Parkway West, Chesterfield, MO 63017 Phone: (636) 537-4000 Website: chesterfield.mo.us/planning-development-services.html

Disclaimer: Zoning regulations change frequently, and flood zone designations can change with FEMA map revisions. Always verify current ADU rules and flood zone status directly with the City of Chesterfield Planning and Development Services and FEMA before beginning any project. This page is for informational purposes only and does not constitute legal or zoning advice.