ADU Rules in Chicago, IL (2026)
ADU rules, permit requirements, size limits, and fees for Chicago, IL. Source-cited from official municipal code.
Yes, ADUs are allowed in Chicago, IL.
Chicago, IL permits accessory dwelling units (ADUs) on residential properties. ADUs — also called granny flats, in-law units, backyard cottages, or secondary suites — are secondary housing units on a single-family or multifamily lot. State and local law governs the approval process. In Chicago, the Chicago Department of Buildings handles ADU permit applications. Below you will find the current size limits, setbacks, fees, and timeline for building an ADU in Chicago.
ADU Size Limits
ADU Size Limits in Chicago: Detached ADU: up to 1000 sq ft (max height: 22 feet). Attached ADU: 700 sqft or no more than the existing unit square footage, whichever is less. Chicago does not use the California JADU framework. Detached coach houses (alley-facing ADUs) limited to 1,000 sqft or 700 sqft depending on district. Basement apartments (conversion ADUs) are a distinct category. Per Chicago ADU Ordinance (O2020-5816, expanded O2022-1679).
| Type | Max Size | Max Height |
|---|---|---|
| Detached ADU | 1000 sq ft | 22 feet |
| Attached ADU | 700 sqft or no more than the existing unit square footage, whichever is less | Per primary dwelling zone height limit |
Permit Fees
ADU Permit Fees in Chicago: Plan check fee: $200–$1,500. Building permit fee: Based on construction value — typically $1,000–$5,000. Impact fees: None. School fees: None or N/A. Total estimated permit cost: $1,500–$6,500 total permit fees. Chicago Department of Buildings fee schedule: https://www.chicago.gov/city/en/depts/bldgs/supp_info/fee_schedule.html
| Fee Type | Amount |
|---|---|
| Plan Check | $200–$1,500 |
| Building Permit | Based on construction value — typically $1,000–$5,000 |
| Impact Fees | None |
| School Fees | None |
| Total Estimate | $1,500–$6,500 total permit fees |
Permit Timeline
Chicago ADU Permit Timeline: Chicago DPD building permit for ADU: typically 3-6 months for plan review. ADU Express program in development. Construction 4-12 months. Apply through the Chicago Department of Buildings online permit portal. Phone: (312) 744-5000.
Setback Requirements
ADU Setback Requirements in Chicago: Front setback: follows zone standard. Side setback: 2 feet. Rear setback: 2 feet. Coach houses must be located behind the principal building and set back 2 ft from rear property line and 2 ft from side property line. No additional front setback required for coach houses (they are in rear yards). Per Chicago ADU Ordinance.
Parking Requirements
Parking Requirements: No replacement parking required when garage is converted to ADU. New detached ADUs (coach houses) typically built over new 1-car garage — no additional parking required per ADU Ordinance.
Restrictions & Requirements
- Owner-occupancy required — must reside on property
- Annual owner-occupancy affidavit required
- ADU must comply with Chicago Building Code habitability standards
- Basement conversions must meet minimum ceiling height (7 ft habitable space minimum)
- Only one ADU per lot (principal building, not counting multi-unit buildings)
- Chicago Affordable Requirements Ordinance (ARO) may apply in certain areas
- Landmark or contributing structure in landmark district requires additional review
How Many ADUs Are Allowed?
Number of ADUs Allowed in Chicago: Single-family lots: 1 ADU per lot. Multifamily properties: Existing 2-flats and larger multifamily have different rules — conversion of existing units vs. new ADU construction. Chicago ADU Ordinance Phase 1 (2021) covered 5 pilot areas. Phase 2 (2022) expanded to entire city. Both attached (basement/attic) and detached (coach house) ADUs permitted citywide.
Single-Family Lots
1 ADU per lot
Multifamily Properties
Existing 2-flats and larger multifamily have different rules — conversion of existing units vs. new ADU construction
Historic District Considerations
Historic District Requirements: Chicago has 70 historic districts where additional design review may be required for ADU construction. Design review approval is required before obtaining a building permit for properties in historic overlay zones. Chicago Commission on Chicago Landmarks designates Chicago Landmark Districts (approx. 70) and Individual Landmarks (approx. 400). Certificate of Appropriateness required for exterior changes to landmarked properties. Notable districts: Landmark District for Pullman, Wicker Park-Bucktown Historic District, Jackson Park Historic Landscape District. Look up historic district boundaries at: https://www.chicago.gov/city/en/depts/dcd/supp_info/chicago_landmarks.html
Frequently Asked Questions
Can I build an ADU in Chicago?
Yes. Chicago, IL allows accessory dwelling units. On a single-family lot you can build 1 ADU per lot.
How big can an ADU be in Chicago?
The maximum size for a detached ADU in Chicago is 1,000 square feet.
How long does it take to get an ADU permit in Chicago?
The typical ADU permit timeline in Chicago is Chicago DPD building permit for ADU: typically 3-6 months for plan review. ADU Express program in development. Construction 4-12 months.. Total estimated permit fees are $1,500–$6,500 total permit fees.
Do I need extra parking for an ADU in Chicago?
No, Chicago does not require additional parking for ADUs.
Do I have to live on-site to have an ADU in Chicago?
No, owner-occupancy is not required for ADUs in Chicago.
Source: Chicago Municipal Code Title 17 (Zoning Ordinance); Additional Dwelling Units Ordinance O2020-5816 as amended by O2022-1679. Last verified April 3, 2026. View source