ADU Rules in Hazelwood, Missouri

Hazelwood is a city of approximately 25,000 people in north St. Louis County, located immediately adjacent to Lambert-St. Louis International Airport (STL). Hazelwood is a primarily residential and light industrial/commercial suburb with a mix of post-WWII residential neighborhoods. The proximity to Lambert Airport is a defining characteristic of Hazelwood's development context and has significant implications for residential construction. 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. Hazelwood sets its own ADU rules through its local Code of Ordinances, zoning chapter.

Lambert Airport Proximity — Critical for ADU Projects

Lambert-St. Louis International Airport (STL) is located directly adjacent to Hazelwood, and portions of the city fall under the airport's flight paths and noise influence areas. This has several implications for ADU projects in Hazelwood:

• Airport Noise Contours: Properties within the airport's noise exposure contour zones (typically the 65 DNL and 70 DNL contours) may be subject to noise attenuation standards for new residential construction. New habitable space — including ADUs — in these zones may require enhanced sound insulation to meet applicable standards.
• Airport Overlay Zones: The Federal Aviation Administration (FAA) Part 77 surfaces and airport influence areas may restrict building heights or require FAA notification for certain structures.
• Historical Context: Lambert Airport was significantly expanded in the 1990s–2000s, and portions of north St. Louis County (including parts of Hazelwood) were affected by airport noise abatement programs.

Before planning an ADU in Hazelwood, confirm with the Department of Community Development whether your property:

• Falls within an airport noise contour zone.
• Is subject to any airport overlay zoning district standards.
• Requires any noise attenuation measures for new habitable construction.

Permitted ADU Types

Hazelwood'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 the primary dwelling creating a separate, self-contained unit.
• Garage Conversion: Converting an existing garage into habitable ADU space.
• Basement or Interior Conversion: Adapting existing interior space within the primary structure, which may be advantageous from a noise attenuation standpoint in airport-adjacent locations.

Permitted types and applicable standards vary by zoning district. Contact the Department of Community Development 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 a square footage cap or percentage of the primary dwelling's floor area per district standards.
• Setbacks: Rear and side yard setbacks for detached accessory structures are district-specific; commonly 3 to 5 feet.
• Height: Detached ADUs are generally limited per district accessory structure height standards; note that FAA height considerations may also apply near the airport.
• Lot coverage: Maximum lot coverage limits apply.

Always verify current standards with the Department of Community Development.

Flood Zone Considerations

Portions of Hazelwood near local waterways 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 ADU construction.

Permit Process

1. Confirm zoning district and airport overlay: Check your property's zoning and any airport overlay zone status using the city's GIS mapping tools or by contacting the Department of Community Development.
2. Verify noise contour zone: Contact Community Development to determine if your property requires noise attenuation measures for new habitable space.
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 an architect or designer; note noise attenuation requirements if applicable.
6. Submit building permit application: File with Hazelwood's Building Division or Department of Community Development.
7. Plan review: Staff reviews for zoning, building code, and any airport overlay 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 Hazelwood Department of Community Development 415 Elm Grove Lane, Hazelwood, MO 63042 Phone: (314) 839-3700 Website: hazelwoodmo.org/community-development

Disclaimer: Zoning regulations change frequently, and airport noise/overlay zones are subject to FAA updates. Always verify current ADU rules and airport influence area requirements directly with the City of Hazelwood Department of Community Development before beginning any project. This page is for informational purposes only and does not constitute legal or zoning advice.