ADU rules in St. Louis, MO — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
St. Louis allows accessory dwelling units in many residential zones through a 2023 zoning code update supporting infill housing.
St. Louis adopted ADU-friendly zoning provisions to encourage housing in its dense historic neighborhoods. ADUs are allowed by-right in most single-family and multi-family zoning districts, including attached (within or connected to the main house), detached (carriage house style), and garage conversions. Typical requirements: unit size capped at 800 sq ft or 33 percent of the primary dwelling (whichever is smaller), one parking space (often waived in transit-served neighborhoods), compliance with historic design standards in Local Historic Districts, separate utility connections or submetering, and a Building Division permit plus Housing Conservation District occupancy permit. Short-term rental use of ADUs is subject to the same STR permit requirements as other units. Owner occupancy of either the main house or ADU is typically required. Coach houses and alley carriage houses are particularly suited to the historic neighborhood fabric.
Unpermitted ADU: stop-work order, $100-$500 fine, required to permit retroactively or remove. Life-safety violations are prioritized.
St. Louis, MO
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See how St. Louis's adu rules rules stack up against other locations.
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