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.
Unit Count Requirements
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.