3 county-level rules, plus city-specific rules for 2 cities in St. Louis County, Missouri.
Verified from official government sources
St. Louis County's Zoning Ordinance §1003.020 defines 'family' as related individuals or a group of no more than 3 unrelated persons. Two kitchens maximum per dwelling unit, which effectively prohibits unpermitted ADUs in standard single-family zoning.
St. Louis County Code §1003.020
Sec. 1003.020. — St. Louis County's Zoning Ordinance defines a family as an individual or two (2) or more persons related by blood or marriage or a group of not more than three (3) persons who need not be related by blood or marriage living together and subsisting in common as a single non-profit housekeeping unit using not more than two (2) kitchens.
A building permit is required for sheds larger than 120 sq ft in unincorporated St. Louis County and in cities that contract for building inspection. Sheds ≤120 sq ft are permit-exempt but must comply with setbacks and the Property Maintenance Code.
St. Louis County Code §1115.105.2
A building permit is required for the construction of all sheds larger than one hundred and twenty (120) square feet in size that are located in unincorporated St. Louis County or in a municipality that contracts with St. Louis County for building code enforcement.
A building permit is required for residential attached or detached garages, attached carports, sundecks, and smokehouses (regardless of size for smokehouses). Smokehouses on residential property are limited to 25 sq ft and 8 ft height.
St. Louis County Code §1115.105.2
A permit is required for all residential smoke houses and similar structures regardless of size. Smoke houses on residential property are restricted to a maximum size of twenty-five (25) square feet in area and eight (8) feet in height and may only be used for cooking (smoking) food for the family on the premises.
2 cities in St. Louis County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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