St. Louis, MO Accessory Structures: ADU Permits (2026)

St. Louis is an independent city (not part of any county) operating under home-rule authority granted by Missouri Constitution Article VI, §31. The City's Zoning Code is codified in St. Louis Revised Code (SLRC) Title 26, with use districts defined in Chapter 26.32 and accessory uses regulated in Chapter 26.60. In 2021, the Board of Aldermen adopted Ordinance 71591 expanding allowed locations and use standards for accessory dwelling units to address housing supply concerns. Under the amended code, ADUs are permitted as accessory uses in the multi-family Two-Family ('B'), Multiple-Family ('C', 'D', 'E', 'F'), and certain mixed-use districts; single-family 'A' districts remain more restrictive. Applications are filed through the City's online permitting system administered by the Building Division (Department of Public Safety). Plan review covers the 2018 International Residential Code (IRC) adopted in SLRC Title 25 (Building, Plumbing and Electrical Code) with St. Louis amendments. Properties in a Local Historic District or Preservation Review District must also obtain a Preliminary or Final review from the Cultural Resources Office and the Preservation Board before a permit issues — STL has numerous designated districts including Lafayette Square, Soulard, Compton Heights, Central West End, Tower Grove East, and others.