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How to build an ADU outside a Chicago pilot area

Aerial photo of Humboldt Drive, and the left/east side is in an ADU pilot area

Chicago's ADU ordinance

An Accessory Dwelling Unit (ADU) is an "extra" home at a residential property. The ADU can be inside the existing building, or a new backyard home on an improved or vacant lot. The City of Chicago adopted an ordinance on December 16, 2020, that removes a majority of the zoning restrictions to building a backyard house or an additional unit (or more than unit) in R-Residential zoning districts.

Pilot areas

To be eligible, a property must be in one of the five pilot areas (Southeast, South, West, Northwest, and North) and be in an "R" zoning district. The RS-1 zoning district is not eligible.

Use Address Snapshot to lookup a property. Once you look it up, scroll down to "Zoning Assessment" and note the zoning district and if it's in a pilot area.

What if my property is not in a pilot area?

If your property is in an R zoning district but not in a pilot area, please first tell your alder that you are interested in building an ADU but you are not in a pilot area. There is no schedule dictating when the program will be expanded or apply citywide.

It's still possible to build an ADU outside a pilot area, but through the normal channel. (However, new backyard houses are not allowed anywhere outside the pilot area.) The next thing to do is conduct a zoning assessment to determine if your property has "unused zoning capacity". There are a couple of standards that dictate how big your house is allowed to be and how many units it's allowed to have.

If your property is in an RS-1 or RS-2 zoning district, you must apply for an upzone. Some alders may help you do that if they agree with your intentions, but most people will need a zoning attorney. You can stop reading this guide.

If your property is in a different "R" zoning district, keep reading, as it may be possible to build an additional unit – either within the existing footprint of your house, or as part of an addition – without applying for an upzone.

The zoning assessment will determine the "Floor Area Ratio" (FAR) of your property which will tell you by how much, if any, your house can expand to accommodate an additional unit. The zoning assessment will also determine the "Minimum Lot Area per unit" number, which dictates how many units are presently allowed. That number, minus the number of current units, tells you how many additional units can be built.

The more important standard is the "Minimum Lot Area per unit" as even if your FAR number does not allow an expansion, a building's basement, attic, or unused first floor space can be converted to a dwelling unit if the "Minimum Lot Area per unit" number exceeds the current number of units. This is called "unused zoning capacity".

Side note: We have a Property Finder map that locates buildings with unused zoning capacity.

How to conduct a zoning assessment

Who can conduct this zoning assessment? First of all, Chicago Cityscape has an automated zoning assessment included with every purchase of an Address Snapshot. Look up your address, then click on tohe "PIN", and purchase that Address Snapshot. In that report, look for the "Housing calculator" which calculates the number of dwelling units allowed on the property. This number is not guaranteed, and only a manually-created zoning assessment can guarantee that.

Chicago Cityscape can conduct individual zoning assessments for a fee of $500. Additionally, most architects can conduct zoning assessments, as can zoning attorneys.