Everything homeowners need to know about building an accessory dwelling unit in Chicago - coach houses, basement and attic conversions, size limits, and how the city's new citywide ADU ordinance actually works.
Last verified: September 2026
6/10 · Moderately ADU-friendly
700 sq ft*
Max ADU size
22 ft
Max height
Required*
Owner-occupancy
By-right*
Permit type
This page summarizes the City of Chicago's citywide Additional Dwelling Unit (ADU) ordinance, effective April 1, 2026, for general reference - it is not legal advice. Regulations change and eligibility varies by ward; always confirm current requirements with the Chicago Department of Buildings and Department of Housing before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Coach house (detached)
Floor area is capped at 60% of the lot's required rear setback area - typically works out to roughly 450 sq ft on a standard lot, more on deeper lots
22 ft, measured to the highest feature
Must sit behind the principal building, within the rear half of the lot
Conversion unit (attached - basement, attic, or above garage)
Up to 700 sq ft, or no more than the existing unit's square footage, whichever is less
Matches the existing structure
Common approach for basement and attic units in two-flats and single-family homes
Where ADUs are allowed
Illinois has no statewide ADU mandate, so Chicago's own ordinance is what governs. Multi-unit residential (RT/RM) zones and certain business/commercial zones allow ADUs citywide, as of right. Single-family (RS) zoned areas only allow ADUs where the local alderperson has opted the ward in - as of mid-2026 that's roughly two-thirds of the city's 50 wards, with more being added over time. Confirm your ward's status with the Department of Housing before you invest in design work.
Additional standards
Setbacks, parking & other rules
Setbacks
Coach houses: 2 ft from rear and side property lines, positioned within the rear half of the lot, behind the principal building
Parking
No additional off-street parking is required for an ADU, even if construction removes an existing parking space
Units per lot
One ADU (a coach house or a conversion unit) in addition to the existing units on the lot, subject to zoning and ward eligibility
Owner-occupancy
Required for properties with two units or fewer (single-family homes and two-flats) - the owner must live in either the primary unit or the ADU. Not required for buildings with three or more units
Building code
Must meet Chicago Building Code standards for habitable dwelling units, including minimum ceiling height
Contractor requirement
Coach house construction requires contractors to participate in a state-approved apprenticeship program - a requirement unique to Chicago's ordinance
Ordinance history
How Chicago's ADU rules got here
1957Zoning rewrite ends new coach houses. A citywide zoning overhaul effectively made it illegal to build new coach houses and similar secondary units, even though many older ones remained standing throughout the city.
2020ADU Pilot Ordinance approved. City Council approved a pilot program allowing ADUs in five designated pilot areas across the North, Northwest, West, South, and Southeast sides.
2021Pilot program takes effect. Starting May 1, 2021, homeowners in the five pilot zones could apply to build coach houses and conversion units, capped at 700 sq ft and 22 ft in height.
2023-24Push for citywide expansion. City Council took up legislation to expand the ADU program beyond the pilot areas, with a substitute ordinance introduced in 2024 to address aldermanic concerns.
2025Citywide ordinance approved. On September 25, 2025, City Council voted 46-0 to convert the pilot into a permanent, citywide program, adding an aldermanic opt-in requirement for single-family zones and a new contractor apprenticeship mandate for coach houses.
2026Citywide ordinance takes effect. Pilot-area boundaries went away on April 1, 2026, and property owners in eligible zones and opted-in wards could begin applying under the permanent program.
Worth knowing: eligibility still depends heavily on where you live. Multi-unit zones are open citywide, but roughly a third of Chicago's wards had not opted in for single-family-zone ADUs as of mid-2026 - check your ward's status before you invest in design work.
Permit process
How Chicago ADU permitting works
1
Confirm ward & zoning eligibility
Check whether your property sits in an as-of-right multi-unit zone or a single-family zone where your alderperson has opted in.
2
Prepare your plans
Site plan, floor plans, and elevations showing the coach house or conversion unit and how it meets the size, height, and setback standards.
3
Neighbor notification
Submit the required neighbor notification affidavit as part of your application package.
4
Submit to the Department of Buildings
File your permit application, including any required ADU program documentation, through the city's online permit portal.
5
Plan review
City staff review for zoning and building code compliance; plan review commonly takes several months, and at least one round of revisions is typical.
6
Permit issuance & inspections
Once approved, construction can begin (with apprenticeship-program contractors required for coach houses); schedule standard inspections through to final approval.
Permit fees, review times, and ward eligibility are changing as the citywide program rolls out - confirm current requirements with the Department of Buildings and Department of Housing before you apply.
Budgeting
What it costs to build an ADU in Chicago
Basement or attic conversion
Roughly $80,000-$180,000, generally the lower-cost path since the shell already exists
Coach house (new detached)
Roughly $200,000-$350,000+, reflecting foundation, utility, and finish work plus Chicago's higher labor costs
Permit fees
Roughly $1,500-$5,000 through the Department of Buildings, plus separate architectural and design costs
Contractor apprenticeship requirement
Coach house construction requires apprenticeship-program contractors, which can narrow your contractor pool and add cost compared to a standard conversion unit
These are general ranges from local contractor estimates and regional reporting, not quotes - Chicago's union-heavy construction market and the coach house apprenticeship mandate tend to push detached-unit costs above the national average.
Before you apply
Tips for a smooth approval
Check your ward's opt-in status first. If you're in a single-family zone, confirm your alderperson has opted the ward into the ADU program before you spend money on design.
Understand which ADU type fits your property. A conversion unit (basement or attic) is usually simpler and cheaper than a coach house, which carries stricter setback, height, and contractor requirements.
Factor in owner-occupancy if you have a smaller building. If your property has one or two units total, you or a qualifying owner will need to live on site.
Budget for the apprenticeship requirement on coach houses. It can narrow your contractor options - get quotes from apprenticeship-program-participating builders early.
Submit a complete neighbor notification package. Missing or incomplete affidavits are a common source of delay in plan review.
FAQ
Common questions
Do I need to live on the property to build an ADU in Chicago?
It depends on your building size. If your property has one or two units total, yes - you must live in the primary unit or the ADU. Buildings with three or more units are exempt from the requirement.
Is my property eligible for an ADU?
Multi-unit residential and certain commercial zones are eligible citywide. Single-family zones are only eligible if your alderperson has opted the ward into the program - confirm with the Department of Housing.
What's the difference between a coach house and a conversion unit?
A coach house is a new detached structure, typically where a garage might go. A conversion unit is built inside the existing building, such as a basement or attic.
How big can a coach house be?
Its footprint is tied to 60% of your lot's required rear setback area rather than a flat number, which typically works out to roughly 450 sq ft on a standard lot, more on deeper lots.
Do I need extra parking for an ADU?
No. Chicago's ordinance does not require additional off-street parking, even if the project removes an existing parking space.
When did Chicago's citywide ADU program start?
City Council approved it in September 2025, and it took effect April 1, 2026, replacing the five-zone pilot program that had run since 2021.
How much does an ADU cost to build in Chicago?
Basement and attic conversions commonly run $80,000-$180,000, while new coach houses often run $200,000-$350,000 or more, given Chicago's labor market and the apprenticeship requirement for coach house contractors, based on local contractor estimates and regional reporting.
Does Illinois have a statewide ADU law?
Not yet. A bill that would limit local governments' ability to restrict ADUs was still moving through the state legislature as of 2025 but had not been enacted - Chicago's own citywide ordinance is what currently governs.
Why does Chicago require an apprenticeship program for coach house contractors?
It's a labor-standards provision unique to the citywide ordinance, intended to ensure coach house construction uses trained workers. It doesn't apply to basement or attic conversion units.
