Can I build an ADU in Chicago?
Answered by AskBaily Editorial · Updated
Short answer
Only in the five designated ADU Pilot zones — Northwest, Northeast, Southwest, Southeast, and West Pilot Areas. Outside those zones Chicago ADUs are prohibited. Coach-house and basement conversions carry distinct rule sets within the pilot zones. CDOB Standard Plan Review + BACP GC license required; CCL review added on landmarked blocks. The pilot is under review for citywide expansion.
In detail
Chicago does not allow accessory dwelling units citywide. ADUs are legal only inside the five Additional Dwelling Unit Pilot Areas — Northwest, Northeast, Southwest, Southeast, and West — established by the May 2021 ordinance that amended the Chicago Zoning Ordinance Title 17 and added new Section 17-9-0118. Outside the pilot footprints, building a coach house or finishing a basement as a separate dwelling is a zoning violation and CDOB will not issue a permit.
Within the pilot zones the rules differ by housing type. Coach houses (rear-yard standalone units above garages or as detached structures) are permitted by-right on lots with an existing principal residence, capped at 700 square feet on most lots and 900 square feet on larger ones, with a 22-foot maximum height. Conversion units (basement or attic apartments inside existing two-flats and three-flats) follow a separate path: in larger buildings of five or more units, owners may add up to one ADU per existing unit, but a fraction must be designated affordable for households at or below 60 percent of Area Median Income. The Department of Housing administers the affordability covenants.
The permitting stack is non-trivial. Every ADU requires a CDOB Standard Plan Review (no Easy Permit path), a BACP-licensed general contractor, a separate egress meeting Chicago Building Code Section 14B-10-1006 (window-well dimensions, stair width, fire separation between units), an independent electrical service or properly sized subpanel, and Chicago Plumbing Code-compliant DWV with a separate water service if the unit has its own kitchen. On landmarked blocks or within a Chicago Landmark District, the Commission on Chicago Landmarks reviews exterior changes before CDOB will route the file to plan review; that adds six to twelve weeks. Coach houses on alleys also coordinate with the Bureau of Forestry on tree-impact review.
The pilot is currently under review by the Department of Housing and the Department of Planning and Development for citywide expansion, but until an ordinance amendment passes City Council, the geographic limitation is hard. Verify your address against the official ADU Pilot Area map before scoping any project.
Sources
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