What's Required in Chicago
- ADUs are allowed by right in RT, RM, business and C1 and C2 districts; in RS districts only within an ADU-Allowed RS Area, which may carry block caps and owner-occupancy requirements.
- Every new conversion unit or coach house starts with a Department of Housing pre-certification, and the approval letter must accompany the DOB permit application.
- The principal building must be at least 20 years old to add a conversion unit; a coach house may only be built after the principal building.
- A property with 1 to 4 existing units may add one conversion unit and one coach house.
- The building permit is plan-based, with plans by an Illinois-licensed architect or structural engineer and zoning approval before DOB review.
- No additional parking is required; short-term rentals are prohibited in conversion units and in coach houses built after 2021.
- When two or more ADUs are added, half must be affordable at 60 percent of AMI for 30 years and registered with DOH at $500 per unit.
- Coach house construction requires the general contractor and all subcontractors to participate in U.S. Department of Labor registered apprenticeship programs.
- Electrical work requires a Chicago-licensed electrical contractor and plumbing a licensed plumbing contractor; a certificate of occupancy is required for buildings of 4 or more units.
Can You Build an ADU in Chicago?
Yes, in most of the city since April 1, 2026. Ordinance SO2024-0008918, passed in September 2025, legalized additional dwelling units by right in all non-single-family residential districts (RT and RM), business districts, and C1 and C2 commercial districts, and let alderpersons opt single-family (RS) districts into ADU-Allowed RS Areas. The city distinguishes a conversion unit, connected to the existing building such as a basement or attic apartment, from a coach house, a separate detached structure. Every project starts with a pre-certification application to the Department of Housing (DOH), which checks eligibility, notifies your alderperson's office, and issues an approval letter that must be included in the building permit application.
The eligibility rules are concrete. A property with 1 to 4 existing legal units may add one conversion unit and one coach house. The principal building must be at least 20 years old to add a conversion unit, and a coach house may only be built after the principal building. In ADU-Allowed RS Areas there may be owner-occupancy requirements and annual block caps of one, two or three pre-certifications per block in RS-1, RS-2 and RS-3 districts, and some projects need a $500 administrative adjustment from Planning and Development. When you add two or more ADUs, half of them (rounding down) must be rented at or below 60 percent of area median income for 30 years, registered with DOH at $500 per affordable unit. To build a coach house, your general contractor and all subcontractors must participate in U.S. Department of Labor registered apprenticeship programs.
Chicago ADU Permit Rules by Scenario
| What you are doing | City filing | Rule |
|---|---|---|
| Basement or attic conversion unit in a two-flat or multi-unit (RT or RM) building | DOH pre-certification, then plan-based DOB permit, $1,800 minimum | ADU ordinance site; Table 14A-12-1204.3(4), Group R |
| Conversion unit in a single-family (RS) district | Only inside an ADU-Allowed RS Area; block caps and owner-occupancy may apply | ADU eligibility and requirements pages |
| New detached coach house in the rear yard | DOH pre-certification, then plan-based permit, $2,450 minimum; apprenticeship-program contractors | ADU requirements; Table 14A-12-1204.3(3), Group R |
| Converting an existing garage into a coach house | DOH pre-certification required, then plan-based permit | DOH pre-certification page |
| Legalizing a basement unit or coach house built without a permit | DOH pre-certification, then plan-based permit | DOH pre-certification page; ADU ordinance site |
| Repairing or adding onto a legally established coach house | No pre-certification; ordinary DOB permit for the work | DOH pre-certification page |
| Adding two or more ADUs on one property | Half must be affordable for 30 years; $500 DOH registration per affordable unit | ADU affordability page |
How Much Does an ADU Permit Cost in Chicago?
An ADU is never an express permit: converting unheated space into living space and changing the occupancy of a space are both excluded from the express interior alteration worktype, so the permit is plan-based and priced by formula, construction factor times scope-of-review factor times area, subject to a minimum. For a conversion unit in a wood-frame two-flat (Group R, Type V, $0.44 per square foot) the rehabilitation table applies a factor of 1.0 for an increase in the number of dwelling units, with a $1,800 minimum: a 900-square-foot basement unit computes to 0.44 x 1.0 x 900 = $396, so the minimum controls and the permit fee is $1,800. A new coach house is new construction; the table's row for residential construction with a maximum of 4 stories and 3 dwelling units carries a 0.75 factor and a $2,450 minimum, and a 700-square-foot coach house computes to 0.44 x 0.75 x 700 = $231, so the fee is $2,450. The non-refundable $600 deposit is paid at submission and the balance at issuance. Add the Title 17 zoning review fee (not published on the permit pages), the $500 administrative adjustment if one applies, and $500 per affordable ADU registration when adding two or more units.
Who Files and What They Submit
You apply to DOH online with the applicant and property information, the number of existing legal units, the year built, the ADU type and count, and, where required, proof of owner occupancy and the affordability covenant and affidavit. After the approval letter, an Illinois-licensed architect or structural engineer designs the unit and prepares the plan-based permit application, which needs zoning approval before DOB review and is assigned a project manager in E-Plan. Construction lists a licensed general contractor, a Chicago-licensed electrical contractor, and a licensed plumbing contractor. A certificate of occupancy is required for buildings of 4 or more units; for 1 to 3 units or a coach house you may request one before inspections. A first inspection must pass within 540 days or the permit expires.
How to Get a ADU Permit in Chicago
Check the eligibility map
Look up the address on the City's ADU eligibility map and zoning map to confirm the district, any ADU-Allowed RS Area limits, and the number of existing legal units.
Apply for DOH pre-certification
Submit the online application with property details, ADU type and count, and any owner-occupancy or affordability documents; your alderperson's office is notified automatically.
Design with a licensed professional
An Illinois-licensed architect or structural engineer prepares the plans and starts the plan-based application in E-Plan after zoning approval, attaching the pre-certification letter.
Pay the deposit and permit fee
The $600 deposit is due at submission; the balance of the $1,800 (conversion) or $2,450 (coach house) minimum is paid when the permit is approved, plus zoning and any adjustment or registration fees.
Build, inspect and occupy
Use licensed contractors (apprenticeship-program contractors for a coach house), request in-progress and final inspections within 540 days, and obtain a certificate of occupancy where required.