Allen Park

Wayne County, MI (1.74M residents - the most populous Michigan county, including Detroit) does not exercise broad zoning authority over its 43 municipalities. Michigan is a strong municipal/township zoning state under the Michigan Zoning Enabling Act (PA 110 of 2006). Wayne County operates a county-level building department (Wayne County Building & Code Compliance) for the small set of unincorporated areas, but most of the county is incorporated. Detroit's ADU rules sit in the Detroit Zoning Ordinance (Chapter 50). Suburban Wayne municipalities (Dearborn, Livonia, Westland, Taylor, Canton Township, Plymouth Township, Northville Township, Redford Township) each set their own ADU rules.

• Michigan Zoning Enabling Act (PA 110 of 2006)
• Detroit Zoning Ordinance (Chapter 50)

State-floor overlay: Michigan has not enacted statewide ADU preemption.

Wayne County administers flood-hazard, and (where mapped) coastal, wildland-fire, historic, and airport overlays that shape ADU project feasibility. The most consistent overlay across the county is FEMA NFIP floodplain regulation; other overlays apply to specific geographies inside the county.

• FEMA NFIP Special Flood Hazard Areas in Wayne County — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; cost impact on the project is often material.
• Historic districts and individually-listed historic resources

Wayne County issues building permits for parcels in unincorporated territory through its development services / planning department, with separate review tracks for zoning conformance, building-code compliance, on-site sewage where applicable, floodplain compliance, and addressing. Inside incorporated municipalities, city departments handle their own permits; the county's authority is geographically limited to unincorporated territory. An ADU permit application is typically processed as a residential building permit with a zoning verification step against the county's ordinance for the parcel's zoning district.