Accessory Structures in O'Fallon, MO (2026)
2 verified accessory structures rules for O'Fallon, Missouri, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
O'Fallon allows a secondary "carriage house" dwelling only inside the Mixed-Use Traditional Development District (MUTDD): City Code § 400.161(B)(4)(a) caps the accessory unit at one dwelling, eight hundred (800) square feet (1,000 on lots of an acre or more), one bedroom, and requires it to stay under the same ownership as the main home.
O'Fallon Carriage House Accessory Dwelling Rules
Significant RestrictionsO'Fallon Code § 400.161(B)(4)(a)
Carriage House. A carriage house means secondary dwelling or office unit located on the same lot as the principal single-family dwelling. ... A carriage house may be an accessory dwelling that is a complete, independent living facility equipped with a kitchen and with provisions for sanitation and sleeping or an accessory office. (1) A carriage house used as a second dwelling ... shall comply w...
Shed & Carport Rules
O'Fallon caps a residential utility shed at 200 square feet and 15 feet in height, keeps it out of the front and side yards, and requires at least a 10-foot rear setback under Zoning Code Section 400.275. Bigger sheds only qualify on R-1A-zoned or 30,000-square-foot-plus lots.
O'Fallon Shed Size, Height And Setback Limits
Some RestrictionsO'Fallon Code § 400.275(A)(2)(c)(1)(e)-(f)
(e) Shall not exceed fifteen (15) feet in height as measured from the adjacent finished grade. (f) Shall not exceed two hundred (200) square feet for a shed or three hundred (300) square feet for a detached garage or carport and the total of all accessory structures shall not exceed fifty percent (50%) of the square footage of the primary structure's building footprint excluding any attached ga...
Looking for St. Charles County county-wide rules?
County ordinances apply to unincorporated areas and may supplement O'Fallon city rules.
Accessory Structures in St. Charles County →