Accessory Structures in St. Louis, MO (2026)
2 verified accessory structures rules for St. Louis, Missouri, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
St. Louis allows one attached or detached accessory dwelling unit per residential parcel, capped at 25 feet in height and 1,200 square feet, and set back at least 3 feet from side lot lines under the zoning code's 2025 ADU standards.
St. Louis Accessory Dwelling Unit Rules
Some RestrictionsSt. Louis Revised Code § 26.20.021(A)
…2.Height.a.The height shall not exceed twenty-five (25) feet.3.Area.a.An accessory dwelling unit may be up to fifty (50) percent of the area of the largest primary dwelling unit on the parcel or seven hundred fifty (750) square feet, whichever is greater.b.An accessory dwelling unit shall be no more than one thousand two hundred (1,200) square feet.4.Density of population.a.Only one (1) access...
Shed & Carport Rules
St. Louis exempts small detached sheds from a building permit only if they are 120 square feet or less, under 12 feet tall, anchored to a 4-inch concrete slab, and set back per the Zoning Code.
St. Louis Shed Size & Permit Rules
Some RestrictionsSt. Louis Revised Code § 25.01.020 (2018 IBC as amended, Section 105.2, item 26)
Small detached accessory buildings, such as utility/storage/tool sheds, cabanas, play houses, etc., 120 square feet in area or less and less than twelve feet in height, provided the utility shed is placed on and anchored to a minimum four-inch-thick concrete slab and maintains the setbacks required by the Zoning Ordinance. This does not include accessory buildings having unique uses such as bar...