Accessory dwelling units, or ADUs, are small homes that are either inside of a building or in a detached building behind a house. Locally they are also called granny flats and coach houses. They were largely made illegal to build in 1957, but since May 2021 have been permitted in five pilot areas. These pilot areas will go away on April 1, 2026, and ADUs will be permitted in more of the city.
Chicago City Council voted 46-0 on September 25, 2025, to approve ordinance SO2024-0008918. Download the ordinance; within a few months after passage the ordinance will be incorporated into the city's online zoning code.
Where in the city does the new ADU ordinance apply?
Starting April 1, 2026, ADUs – in both interior form, which the zoning code calls "conversion units", and in detached house form, which are called "coach houses" – will be permitted in the initial eligibility area. The initial eligibility area covers 29 percent of Chicago, whereas the current pilot program covers only 12 percent of the city.
The initial eligibility area, shown in green on the map below, comprises:
For RS zoning districts outside of the five Pilot Areas, shown in purple in map below, the ADU ordinance uses an "opt in" system. Today’s Pilot Areas are considered “pre-opted-in,” effective April 1.
Learn more about Chicago's zoning districts and where they are on Second City Zoning.
How can the eligibility areas expand?
The eligibility area of RS zoning districts outside the current five current Pilot Areas can be expanded by ordinance. An expansion ordinance will be introduced by an alderperson, approved by the Zoning Committee, and then approved by City Council, and it must include the following information:
An administrative adjustment is a process that requires an application to show specific documentation to the city's Zoning Administrator to gain approval. In this case, the specific documentation required likely comprises building plans showing where on the property an ADU will get built, a snippet of the zoning map showing that the property is in an eligibility area where the rule applies, and a statement indicating how all of the general criteria of section 17-13-1007-B in the zoning code are being met. The administrative adjustment also requires a $500 fee.
How many ADUs are allowed on my block?
Starting April 1, 2026, and assuming no expansion ordinances are passed by then, only RS zoning districts inside three of the five Pilot Areas limit how many ADU permits can be issued per block per year.
The South, West, and Southeast Pilot Areas will all use the aforementioned limitation even after the pilot program converts to a permanent program.
When an alderperson decides to expand the eligibility area to permit ADUs in RS zoning districts in their ward outside of the five Pilot Areas they must indicate if the above ADU permits per block per year limitation applies (as described in the previous question).
North and Northwest pilot areas have no cap on the number of ADU permits issued per block per year. Those areas have had no instances of blocks averaging more than one ADU permitted per year (in the period May 1, 2021, to September 29, 2025).
What are the unique rules based on location?
All properties in RT, RM, B1, B2, B3, C1, and C2 zoning districts are permitted to have one or more ADUs. (The number of ADUs allowed at a property depends on its current dwelling unit quantity, question below.)
Rules may be distinct if a property is in an RS zoning district. All properties that are both within Pilot Areas and in RS zoning districts are permitted to have one or more ADUs. Properties that are in the South, West, and Southeast Pilot Areas will have a limit on the number of ADUs that can be permitted per block per year (see previous question), and houses that have one, two, or three dwelling units will have an owner occupancy restriction (the owner must reside at the property at the time of ADU permit issuance).
Additionally, when alderpersons opt-in RS-zoned blocks to the eligibility area they can choose which limitations apply to properties on those blocks (see question above).
How old does my building have to be to have an ADU?
Buildings must be at least 20 years old to have an interior ADU.
There is no age requirement in order to have a coach house.
How many ADUs are allowed on my property?
The number of interior ADUs is determined by formula: multiply the number of existing dwelling units* by 0.33. See table 1 below for practical calculations for common building sizes. When a building is allowed to have two or more units, one of those units can be in a coach house.
| Extant units | New ADUs allowed |
|---|---|
| 1-4 units | 1 coach house or 1 interior ADU |
| 5-7 units |
Up to 2 ADUs (1 can be a coach house) If 2, 1 must be subsidized affordable |
| 8-10 units |
Up to 3 ADUs (1 can be a coach house) If 2 or 3, 1 must be subsidized affordable |
| 11+ units |
4 or more ADUs are allowed (multiply extant units by 33%) (1 can be a coach house) 50% must be subsidized affordable |
Note: If this 33% calculation results in a fractional number, any fractional result of 0.5 or more must be rounded up to the next consecutive whole number; and any fractional result of less than 0.5 must be rounded down to the previous consecutive whole number. For detached houses where the result would be 0.33 which rounds down to 0, one interior ADU is allowed.
*Existing dwelling units must be legally established in the building for 20 years or more and are not themselves an ADU permitted as a result of this ordinance.
In which mixed-use buildings can an ADU go as a ground floor interior unit?
Mixed-use or commercial buildings in B2 zoning districts can have dwelling units on the ground floor by right, permitted normally and not via the ADU ordinance. For the same kind of buildings in B1, B3, C1, and C2 zoning districts a ground floor interior ADU is allowed by right if 40 percent or more of the building's street frontage is devoted to commercial use. If the street frontage standard is not met, then the interior ADU can be built as a special use (permission granted by the Zoning Board of Appeals).
Who can decide what can or can't be built?
In the eligibility area, ADUs will be permitted by right after receiving pre-approval certification from the Chicago Department of Housing and a building permit from the Chicago Department of Buildings. The eligibility area can be expanded by ordinance introduced by an alderperson; a previous answer describes the expansion process in more detail.
Can an alderperson who opted into allowing ADUs in RS zones change their mind and ban them again? Or if a new alderperson takes office, can they choose to ban them again? What happens to ADUs under construction if that happens?
After opting an area into the eligibility area (which must happen via ordinance explained above), the same or a future alderperson could introduce an ordinance to undo that or change the extent of the eligibility area.
An ADU that's under construction or is still in the permit review process will not be affected as the zoning code and eligibility area that was in place at the time a building permit application number was generated applies.
When will the ordinance become effective and when can I apply for a building permit?
The new citywide ADU ordinance will become effective on April 1, 2026. That's also the same day that building permit applications can be submitted.
How can an illegal unit become legal?
An "illegal unit" is often an apartment that was built without a permit. Additionally, such dwelling units may not meet current building code standards (which regulate structural stability, life safety, minimum ceiling heights, minimum bedroom size, and where windows have to be installed) or building code standards that were in place at the time the apartment was built.
The dwelling unit can be made legal by applying for a building permit, which will need to have architectural plans that show how the dwelling unit meets building code standards. The unit will be subject to inspection and features in the unit will need to be modified to match what is in the plans (i.e. the unit needs to be “brought up to code”).
How do I add an ADU to my bungalow?
Many bungalows in Chicago were built with "pre-ADUs", basements that can be easily converted to and from additional dwellings. These bungalows have an entrance to the basement from the outside, so tenants and visitors can enter the downstairs unit directly and without having to share space with the main unit; they were built with 7' high ceilings; and many have kitchens or space for a kitchen.
To be recognized as an ADU by the city the owner has to submit a building permit application (see previous question). Unofficially, the pre-ADU could already meet most building code standards and thus are unlikely to be cited for a building violation. An architect or structural engineer can evaluate the basement for adherence to building code standards.
Do I need a parking spot for my ADU?
Parking is not required to be added for any ADU.
In some cases existing parking may be removed. The ADU ordinance allows for removing existing parking on a lot when the owner is building or expanding a coach house on the same lot; permission would be obtained through the administrative adjustment process.
What are the ADU affordability requirements?
Affordability requirements apply when a property has two or more ADUs. In this case the property owner must rent fifty percent of units (rounding down) at a rate, set by the city annually, affordable to a household earning 60 percent of the area’s median income. The ordinance does not say which unit has to be rented at the affordable rate, but affordable rents are set by the city based on the number of bedrooms and who pays for utilities. (View the 2025 rent charts.)
What are the labor requirements for building a coach house?
The ordinance requires that a property owner obtaining a building permit for a coach house “has committed and agreed to obligate the general contractor, and any subcontractors retained, to participate in Registered Apprenticeship Programs which are approved by and registered with the United States Department of Labor’s Office of Apprenticeship…for the trades that will perform work under the permit.” There are no exceptions to this requirement.
As of October 2025, approximately 24 companies in Chicago participate in a Registered Apprenticeship Program (RAP), according to the U.S. Department of Labor.
Can I build an accessible ADU?
Yes, an ADU can be built so it's accessible to seniors and people with disabilities. There is no requirement to do so. Coach houses can also be built on the ground level, in place of or next to car parking, for step free access.
How big can a coach house be?
The floor area of a coach house is limited to 60 percent of a property's required rear setback, which is usually 30 feet (but this depends on the property's zoning district). On a standard size lot that's a cap of 450 s.f. Owners of larger lots can have bigger coach houses.
The height of the coach house is limited to 22', and is measured to the top of the highest feature, and not the zoning code's regular method of measuring building heights.
Where are the Pilot Areas and what will happen to them?
The five Pilot Areas are called North, Northwest, West, South, and Southeast, and cover about 12 percent of Chicago. They will functionally dissolve on April 1, 2026, while also forming the initial ADU eligibility area for RS zoning districts.
The West, South, and Southeast pilot areas will carry over certain rules: an owner occupancy requirement when adding an ADU to a house with 1 to 3 units, and a cap on the number of ADU permits per block per year (one in RS-1 zoning districts, two in RS-2, and three in RS-3).
How many ADUs have been permitted in each of the pilot areas?
Building permits data provided by the Chicago Department of Buildings, collected by Chicago Cityscape, from May 1, 2021, to September 28, 2025, is shown below in table 2.
| Pilot Area | Permits | Units |
|---|---|---|
| North | 183 | 208 |
| Northwest | 163 | 192 |
| West | 12 | 14 |
| South | 15 | 21 |
| Southeast | 1 | 1 |
What share of those pilot builds would’ve involved the labor requirements?
According to tracking by Chicago Cityscape, 22 percent of the ADUs permitted were coach houses (May 1, 2021, to September 28, 2025). If those would have been permitted on or after April 1, 2026, the labor requirement would have applied.
How could this affect my property tax assessment?
Property owners who add an ADU should consider that the assessed value of the property may increase, much like if another improvement (such as adding a dormer) were made. Additionally, property classifications may change. For example: a property that has a classification of detached house that gains an interior ADU may have its classification change to that of a two-flat.
Cook County Assessor Fritz Kaegi said, “Construction of a new ADU in one home will not cause higher assessments for neighbors who have not built ADUs.” Additionally, a portion of the value of the ADU can be exempted for up to four years. Homeowners should ensure that a Home Improvement Exemption was applied by the Cook County Assessor’s Office, which will automatically apply the exemption; the office receives copies of building permits and will check for improvements in the field.
Can I use an ADU for a short term rental, like on Airbnb, VRBO, or Booking.com?
Chicago doesn't allow ADUs – specifically those dwelling units permitted pursuant to the ADU ordinance – to be used for short term rentals, with no exceptions.
