# Unused Zoning Capacity: How to build additional dwelling units Building one or more additional units at a residential or mixed-use property in Chicago often requires a zoning change – which is costly, takes a lot of time, and can have an uncertain outcome. Many properties, however, have "unused zoning capacity", where the zoning district of a property allows more to be built than is extant. There are two primary ways and one secondary way to build additional units: 1. Chicago's ADU ordinance, where additional units can be added when there's not unused zoning capacity 2. Unused zoning capacity 3. Zoning relief (including rezoning) ## 1. 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. ### ADU pilot areas To be eligible, a property must be in one of the [five pilot areas](http://chicagocityscape.com/maps/index.php#/?places_type=chicagoadupilotarea) (Southeast, South, West, Northwest, and North) and be in an "R" zoning district. The RS-1 zoning district is not eligible. Use [Property Report](http://chicagocityscape.com/address.php) 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 alderperson 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 interior 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. #### Your property is in a RS-1 or RS-2 zoning districts If your property is in an RS-1 or RS-2 zoning district, you must apply for an upzone. Some alderpersons 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, but Chicago Cityscape can recommend a zoning attorney for you. #### Your property is in another R zoning district 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". (Read our <a href="https://twitter.com/search?q=%23unusedzoningcapacity%20(from%3Achibuildings)&src=typed_query&f=live" target="_blank">tweets tagged with #UnusedZoningCapacity</a> to see examples of where property owners have taken advantage.) ## 2. How to determine if a property has Unused Zoning Capacity Chicago Cityscape has an automated zoning assessment included with every purchase of a Property Report. [Look up your address](http://chicagocityscape.com/address.php), then click on the "PIN", and purchase that Property Report. 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. The main way that "unused zoning capacity" is determined is by comparing three metrics: 1. The zoning district (RS-3, for example) 2. The "Minimum Lot Area per unit" standard of that zoning district (this differs based on zoning district) 3. The lot area, which you must get from your survey. Chicago Cityscape's lot area measurements are fine for this exercise, but they do not have the same accuracy as a survey, and any building permit application will require a survey. For example, the RT-4 zoning district is very common in Chicago and it allows one dwelling unit per 1,000 s.f. of lot area. If your lot's area is 3,000 s.f. then three dwelling units are allowed. If the lot's area is 4,000 s.f. then four dwelling units are allowed – being in an ADU pilot area is not necessary to take advantage of this. *See also: 3.c. in Zoning relief below.* Resource: [Information on how to request and apply for an administrative adjustment](https://www.chicago.gov/city/en/depts/dcd/supp_info/administrative_adjustments.html). ### Find properties with unused zoning capacity - [[Value add properties|Refer to the Knowledge Base article about "value add"]] - See the properties listed on the [#UnusedZoningCapacity tag & topic page](http://chicagocityscape.com/tag/unusedzoningcapacity) ## 3. Zoning relief for additional or legalizing units There are a few methods of "relief" from the Chicago zoning code standards. ### a. six units or fewer Buildings with six units or fewer that are 50 years old or older that have evidence of one or more additional dwelling units beyond that shown on the zoning certificate (or recognized through building permit history) may be issued a permit to legalize one addition dwelling unit. The complete code section is in [17-13-1003-BB](https://codelibrary.amlegal.com/codes/chicago/latest/chicagozoning_il/0-0-0-51818). ### b. buildings with any number of units The Zoning Administrator can waive "bulk [a defined term] and density [another defined term] standards within any zoning district under" certain conditions: "the parcel of land is presently improved with a nonconforming structure that has been in existence for at least 50 years; the waiver does not permit more than a cumulative 10% increase in the bulk and density that has been in existence for 50 or more years; that, in the opinion of the Zoning Administrator, the application complies with all applicable approval criteria for variations, as described in Sec. 17-13-1107." This exemption is notably harder to obtain than (a) above, as it requires more documentation and showing how the proposed increase in units complies with the approval criteria for variations. (Variations are under the purview of the Zoning Board of Appeals and this is a rare instance when the Zoning Administrator can instead grant the relief.) This exemption would likely not be used for buildings with fewer than nine or ten units because the limit is a 10 percent increase and an eight unit becoming a nine unit building is more than a 10 percent increase. [See section 17-14-0202-L in the zoning code](https://codelibrary.amlegal.com/codes/chicago/latest/chicagozoning_il/0-0-0-52099). ### c. administrative adjustment option The zoning administrator can, through the #administrative-adjustment process, allow for property owners to reduce their minimum lot area requirement by up to 10% if the lot area is the sole reason for a development not being allowed. Example: If the lot area of a property in RT-4 is 3,600 s.f., then four dwelling units may still be allowed due to the ability to request an "administrative adjustment" to reduce the minimum lot area requirement by up to 10 percent (see section 17-13-1003-A in the Chicago zoning code). [See section 17-13-1003-A in the zoning code](https://codelibrary.amlegal.com/codes/chicago/latest/chicagozoning_il/0-0-0-51818) ### d. proving existing density See [section 17-13-1003-BB in the zoning code](https://codelibrary.amlegal.com/codes/chicago/latest/chicagozoning_il/0-0-0-51818), which states: In the case of building permit applications for the repair, remodeling, or alteration of a residential building that has been in lawful existence for 20 or more years and in which there is sufficient documentary evidence provided to the Zoning Administrator that the residential building has been converted, altered or used for at least the previous 20 years from the date of application pursuant to this Section for a greater number of dwelling units than existed at the time of construction of the residential building, the Zoning Administrator is authorized to approve an administrative adjustment to make zoning certification for the total density not to exceed more than 1 unit above its original construction. Sufficient documentary evidence has been known to include: - historical building permits - water service records from the Chicago water department - [U.S. Census records](https://www.stevencanplan.com/2023/03/determining-dwelling-unit-count-at-an-address-using-1950-census-records/) ### e. rezoning (zoning map amendment) The most common way is to rezone the property by proposing a zoning map amendment in an ordinance, also called a zoning change application. This requires an act of City Council and generally requires the support of the local alderperson who will usually submit the ordinance. Please [contact a zoning attorney](http://chicagocityscape.com/members.php?tag=zoning_attorney) for assistance. Chicago Cityscape can make recommendations. ## f. ground floor residential Refer to the [[Converting ground floor commercial to residential via Administrative Adjustment]] article. ## Related articles - [[Parking reductions]] - [[Properties that require less parking]]