O'Fallon, MO Accessory Structures: Shed & Carport Rules (2026)

275(A)(2) governs detached private residential garages, carports, utility sheds, gazebos, pavilions and similar accessory structures, applying to all residential development except the Mixed-Use Traditional Development District and Mobile/Manufactured Home Park Districts. These structures cannot sit in a required front or side yard, must stay at least ten feet from the rear property line, must meet the principal structure's side yard setback, and cannot intrude into a required bufferyard. Height is capped at fifteen feet measured from adjacent finished grade. Size is capped at 200 square feet for a shed or 300 square feet for a detached garage or carport, and the combined footprint of all accessory structures on a lot cannot exceed 50% of the primary structure's building footprint, excluding any attached garage.

A doorway sized for a licensable automobile is treated as conclusive proof the structure is a garage, which also requires a paved driveway. Structures that need to exceed these size or height limits are only allowed on property zoned R-1A or on residential lots larger than 30,000 square feet, and even then must meet the primary structure's setbacks and development standards for that zoning district. Any utility shed over 200 square feet, plus all detached garages and carports, must also be built with materials and architecture substantially matching the primary structure, as the Administrative Officer determines.