Building an ADU in Chicago

What you can build here

Chicago's code splits ADUs into two types. A conversion unit is connected to the existing building, for example in an attic or basement. A coach house is a separate, detached building, sometimes called a backyard house, granny flat or carriage house.

Chicago banned new ADUs starting in 1957. The City Council first approved an ADU ordinance in 2020, which created five ADU pilot areas. In September 2025 the Council voted to expand ADUs beyond the pilot program. That ordinance (SO2024-0008918) took effect on April 1, 2026.

ADUs are now allowed by right in all residential two-flat, townhouse and multi-unit (RT) and multi-unit (RM) districts, and in B2 and certain other business and commercial districts. In B1, B3, C1 and C2 districts, a conversion unit below the second floor is allowed by right only if at least 40% of the ground floor facing the street is in commercial use; otherwise it needs a special use. Conversion units above the ground floor are allowed by right in all B, C1 and C2 districts. [1][2][3][5][6]

Single-family (RS) lots: ADU-Allowed RS Areas

If your lot is zoned RS1, RS2 or RS3, you can add an ADU only if it is inside an ADU-Allowed RS Area. The City Council creates and changes these areas by ordinance, and they are listed in Section 17-7-0574 of the zoning code. The current code lists ten areas, after amendments in December 2025 and February 2026. Check your address on the ADU eligibility map.

Some areas add one or more of these limits:

• Annual block cap: no more than 1 (RS1), 2 (RS2) or 3 (RS3) conversion units and coach houses combined may be pre-certified on the same block face and opposite block face in a calendar year.
• Owner occupancy: if the main building is a detached house, the owner must live in it at the time of pre-certification. You prove this with a government photo ID plus one document such as a property tax bill, utility bill, deed, mortgage statement or homeowner's insurance declaration.
• Administrative adjustment: no ADU without an administrative adjustment from the Zoning Administrator, which costs $500.

In the current table, Areas 1, 6 and 7 have none of these limits. Areas 3, 4, 5 and 10 have the block cap and owner-occupancy limits. Area 2 has owner occupancy and the administrative adjustment. Areas 8 and 9 have all three. Confirm the limits for your address with the DOH ADU team before you design. [2][4][7][8]

How many ADUs you can add

Conversion units. The main building must be at least 20 years old. You can add 33% more units than the number of legal units that have existed in the building for 20 or more years, and a single-unit building can add one. The city's table:

• 1 to 4 existing legal units: one conversion unit
• 5 to 7 units: two conversion units
• 8 to 10 units: three conversion units
• 11 to 13 units: four conversion units

Coach houses. You can add one coach house, alone or together with conversion units, regardless of the main building's age. A coach house may not be built on a lot before the main building. For example, the city says a four-unit building built in 2005 could add one conversion unit and one coach house. [3][7][9]

Coach house size, placement and setbacks

• Spacing: at least 15 feet between the rear wall of the main building and the front wall of the coach house. On lots less than 125 feet deep, this can be cut to no less than 10 feet by administrative adjustment, with support from DOB and the Fire Department.
• Rear setback: a coach house may sit in the required rear setback. Next to a public alley it must be at least two feet from the rear property line, unless it is at least ten feet from the alley's centerline.
• Business and commercial districts: a coach house may only go in the rear 30 feet of the lot.
• Density limits: coach houses are exempt from the minimum lot area and floor area ratio rules. They are exempt from the open space rules too, but may not reduce open space the main building needs.
• One unit: only one dwelling unit is allowed per coach house.

The 2025 ordinance deleted the earlier rule that capped a coach house unit at 700 square feet. It did not change other coach house standards in Section 17-9-0201-F, such as height. Ask the Office of the Zoning Administrator at (312) 744-5777 to confirm the height and size limits for your lot. [3][10][11][12]

Parking

You don't need to add parking for a conversion unit or a coach house. The zoning code says conversion units "may be established without corresponding accessory parking."

If building a coach house would affect parking required for the main building, that requirement can be reduced or waived through an administrative adjustment. [3][6][7][11]

Affordability rules when you add two or more ADUs

If you add two or more ADUs, in any mix of conversion units and coach houses, 50% of the new units (rounded down) must be kept affordable for 30 years. You choose which units. Affordable ADUs must be rented to tenants at or below 60% of area median income (AMI).

For 2026, the city's maximum gross monthly rent at 60% AMI, when the landlord pays all utilities, is $1,367 for a one-bedroom and $1,641 for a two-bedroom. See the 2026 income and rent limits.

You register each Affordable ADU with DOH ($500 each), upload a signed affordability covenant and compliance affidavit with your pre-certification application, and record the covenant with the Cook County Clerk. You file a compliance affidavit every year. The code sets a $500 fine for each day of a violation and lets an aggrieved tenant sue. [3][13][14]

Fees and timeline

• Affordable ADU registration (only if you add two or more ADUs): $500 for each Affordable ADU.
• Administrative adjustment (only where required): $500.
• Building permit: based on construction type, occupancy type, square footage and project scope. Use DOB's permit fee calculator. New fee tables apply to permits issued on or after January 1, 2027.
• Zoning opinion letter (optional): $150, and up to 30 days to process.

The city doesn't publish a fixed review time for ADUs. DOB posts real-time average issuance times for plan-based permits on its home page, and it processes applications in the order received. Where an administrative adjustment is needed, the Zoning Administrator can't act until at least 10 days after notices are mailed to neighbors and the alderman. For budgeting, see our ADU cost guide. [3][7][12][13][15][16][17]

Existing coach houses and garage conversions

You don't need DOH pre-certification to repair, remodel or add on to a legally established coach house. That means one built under the laws in force at the time and continuously occupied as a dwelling.

You do need pre-certification to:

• build a new coach house;
• convert an existing garage or similar detached building into a coach house;
• bring back residential use in a building historically used as a coach house;
• legalize a coach house built or converted without a permit.

See our garage conversion guide for the general steps. [18]

Renting it out

You can't use a conversion unit, or a coach house established after May 1, 2021, as a short-term or vacation rental, such as Airbnb. The code bans transient rentals in conversion units and in coach houses lawfully established after May 1, 2021, except to members of the owner's or tenant's household. Fines run from $1,500 to $3,000 per offense, and each day counts as a separate offense.

Long-term rentals are allowed. If you add two or more ADUs, the affordability rules above apply. For state-level rules, see our Illinois page. [3][6][7]

Permit steps in Chicago

1. Check eligibility

   Look up your address on the city's ADU eligibility map and your zoning on the Chicago Zoning Map. The ADU Allowance by Zoning District chart shows which districts allow each type. [2][5]

2. Check the limits that apply to your lot

   On RS-zoned lots, check whether your ADU-Allowed RS Area has an owner-occupancy rule, an annual block cap or an administrative adjustment requirement. Check your building's age and number of legal units to see how many ADUs you can add. See the city's ADU requirements page. [7]

3. Get an administrative adjustment, if required

   In areas that require one, apply to the Zoning Administrator in the Department of Planning and Development. The fee is $500. See DPD's administrative adjustments page. [7][8]

4. Apply to DOH for ADU pre-certification

   Apply online through the ADU pre-certification portal. You give the number of existing legal units, when the building was built, and the type and number of ADUs, and upload any owner-occupancy or affordability documents. Your alderperson's office is emailed automatically when you submit. [7][21]

5. Record affordability documents, if required

   If you are adding two or more ADUs, upload the affordability covenant and compliance affidavit, record the covenant with the Cook County Clerk, and pay the $500 registration fee for each Affordable ADU. [13]

6. Hire a licensed architect or engineer

   A licensed architect or structural engineer designs the ADU to Chicago's building and zoning codes. Only an Illinois-licensed architect or engineer, or a City-licensed expediter, can apply for a plan-based building permit. [19][20]

7. Apply to DOB for a building permit

   Submit the plans and your pre-certification approval letter for a plan-based permit, usually through the Standard Plan Review program in E-Plan. Revise the plans if reviewers ask, then pay the permit fee when the permit is approved. [19][21][22]

8. Build, pass inspections and file yearly affidavits

   Build with licensed contractors and request in-progress and final inspections. A coach house requires your contractors to take part in registered apprenticeship programs. If you have Affordable ADUs, file an annual compliance affidavit with DOH. [3][7][19]

Who to call

• Department of Housing (DOH)

  Eligibility, pre-certification and affordability questions; email the ADU team at ADU@cityofchicago.org

  312.744.3653

  121 N LaSalle St, Room 1000, Chicago, IL 60602

  [1][23]

• DPD Office of the Zoning Administrator

  Zoning questions, administrative adjustments and zoning opinion letters; email DPD_Zoning@cityofchicago.org

  (312) 744-5777

  121 N LaSalle St, Room 905, Chicago, IL 60602

  [12]

• Department of Buildings (DOB)

  Building permits and inspections; email dob-info@cityofchicago.org. The 9th-floor front desk at City Hall answers general questions Monday to Friday, 8:30 a.m. to 4:30 p.m.

  City Hall, 121 N LaSalle St, 9th floor, Chicago, IL 60602

  [17][20]

• City of Chicago 311

  General city services line; dial 311 in Chicago

  312.744.5000

  [24]

Questions people ask