Additional Dwelling Units (ADU) Ordinance

The Additional Dwelling Units (ADU) Ordinance, approved by the Chicago City Council in December 2020, expands housing access across Chicago by allowing ADUs in attics, basements, and accessory buildings. Common names for these type of housing units include coach houses, backyard houses and in-law apartments.

ADUs were common in Chicago throughout the first half of the 20th century, but their construction was prohibited starting in 1957 due to changes in the zoning ordinance that added parking requirements and banned secondary residential structures on Chicago lots.

The ADU ordinance allows for the creation of new units for homeowners needing extra income, or those who wish to create separate spaces for multi-generational families. It also provides a path for legalization of units that were previously built without zoning approval and building permits.

In addition to the geographic requirement, properties must also:

• Be at least 20 years old if adding a conversion unit in basement or attic space
• Be located in a residential zoning district — either an RM, an RS or an RT — with the exception of RS-1, single family housing

To find the zoning of a property, search the address on the City of Chicago Zoning Map. 

The ordinance allows ADUs to be constructed on properties that have existing, legal residential units. It also makes a distinction between coach houses, which are new units created in a detached building in the backyard, and conversion units, which are new units constructed in an existing principal residential building that is at least 20 years old, typically in attic or basement space.

The number of ADUs allowed depends on the number of existing legal units on a property:

• For properties with 1 to 4 units, the property owner can add one coach house unit to any property, or one conversion unit to properties that are at least 20 years old
• For properties with 5 or more units, coach houses are not permitted, but the property owner can create up to 33 percent more units as conversion units

Affordability Requirements and Opportunities

For properties with two or more conversion units, every other unit must be legally restricted affordable at 60 percent Area Median Income (AMI) for 30 years after its construction. Properties with two or three conversion units must have one affordable unit, properties with four or five conversion units must have two affordable units, and so on. 

Additional key regulations are listed below.

• No additional parking is required for newly created ADUs
• No existing on-site parking can be removed to create ADUs without administrative adjustments or other zoning relief
• No short-term leases or vacation rentals, such as Airbnb, are permitted in ADUs
• Coach houses may cover no more than 60 percent of a property’s required rear setback and may contain no more than 700 square feet of living space
• No elements of a coach house can exceed 22 feet in overall height above grade
• ADUs are exempt from minimum lot area per unit rules
• In the North and Northwest zones, vacant lots can have coach houses constructed before a principal residence, but this is not permitted elsewhere
• In the West, South and Southeast zones, buildings with one to three units must be owner-occupied in order to add a conversion unit
• In the West, South and Southeast zones, buildings must be owner-occupied in order to add a coach house
• In the West, South and Southeast zones, only two ADU permits will be issued per block per year

Building permit applications for an ADU must include plans prepared by an Illinois-licensed architect or structural engineer. The architect or engineer may submit the permit application directly to the Department of Buildings (DOB) or may work with a City-licensed permit expediter to do so.

A property owner may also hire a general contractor; however, they may be eligible to act as their own general contractor if the property will have less than six units after the ADU work is complete. City-licensed electrical, plumbing and mason contractors are required for electrical, plumbing or masonry work to be performed under the permit.

An initial intake application will be reviewed by the Department of Housing (DOH) prior to the typical permitting process through the Department of Buildings (DOB). An approved intake application doesn't signify authorization to commence construction. It allows the applicant to proceed with submitting a building permit application to DOB. Certain applications for an ADU may require a zoning opinion letter from the Department of Planning and Development (DPD) to affirm the quantity of legally established units if acceptable records cannot be produced by the applicant.

Additional questions about the ADU Ordinance and the upcoming application period can be directed to adu@cityofchicago.org.

You can begin the application process to add an ADU to your property here.