Chicago's skyline is pictured in this file photo.

An ordinance to formally end a nearly 70-year ban and broadly legalize attic and basement conversion units and coach houses citywide goes into effect Wednesday, with the city launching a webpage to inform property owners interested in participating of their eligibility and program requirements.

The ordinance (SO2024-0008918), approved by the City Council in September, allows property owners to construct additional dwelling units (ADUs) by right in multi-unit residential zoning districts and in many business and commercial zones by right or with a special use permit depending on the location of the unit. It also allows ADUs in single-family zoning districts in over two-thirds of the city’s 50 wards. 

It expanded upon the pilot program, which partially overturned the ban when it launched in 2021, but also made modifications to make it easier to add ADUs in more places. 

Matt Stern, a deputy commissioner for the Chicago Department of Housing (DOH) who oversees the policy, planning and implementation bureau, told The Daily Line the legalization ordinance expanded the number of parcels that allow ADUs from about 115,000 to 321,000. 

Related: Zoning committee hears about successes, challenges of ADU pilot as council considers measure to expand ADUs citywide 

Under the approved ordinance, conversion units can be added to buildings that have been used as residential housing for at least 20 years. 

Coach houses are permitted by right in most cases in those allowed zoning districts, with the main restrictions being that coach houses in business and commercial zones need to be located in the rear 30 feet of a lot, may not be built before the principal building they accompany, and coach house construction must be done by contractors that participate in a U.S. Department of Labor-approved apprenticeship program. Coach houses may only contain one dwelling unit.  

While ADUs are welcome in multi-family districts, single-family zoning districts will operate under a patchwork of regulations that are ward-specific, which was a major compromise made to ensure the ordinance got over the finish line.  

Related: Quinn, Lawson reach compromise on ordinance to broadly legalize conversion units and granny flats citywide with special carveouts for single-family zones 

If a single-family zone was not included in the 2021 pilot, individual alderpeople had to opt all or parts of the single-family areas in their wards into the ADU program. Since September, more than 20 alderpeople have opted some or all of their wards into the program, resulting in at least 34 wards where all or some of the single-family zones will allow ADUs.

However, the rules won’t be the same in every single-family zone, as alderpeople also got to choose various restrictions for those districts under the ordinance. The single-family zones where ADUs are allowed have been broken down into 10 distinct areas. Each has their own combination of restrictions, such as limitations on the number of new ADUs that could be pre-certified annually, requiring an ADU to go through the administrative adjustment process or requiring ADUs that are detached houses to be owner-occupied. Some of the areas have no restrictions. 

Conversion units will be allowed in all “B” zoning districts and in the C1 and C2 districts. They will be allowed by right in B2 districts, and in the other districts, conversion units will be allowed by right below the second floor of a building, if at least 40 percent of the ground floor space fronting the public way is still devoted to commercial use. Otherwise, a special use permit would be required for a ground floor conversion unit in B1, B3, C1 and C2 districts.  

However, conversion units above the ground floor are allowed by right in all B districts and in C1 and C2 districts.

The number of ADUs that a qualifying property can add depends upon a formula laid out in the ordinance. The number of conversion units added to a building may not exceed 33 percent of the existing units that are not conversion units, if the building has any already.  

That means buildings with one-to-four dwelling units may build just one conversion unit. Buildings with five or more dwellings may build more, up to that 33 percent threshold. 

But those buildings could also add a coach house, as the ordinance going into effect removed a prohibition on building a coach house and conversion units on the same lot. 

Regardless of building size, just one coach house could be added, but the ordinance removed a previous ban on building coach houses to accompany buildings with five or more units. 

Additionally, when two or more ADUs are added to a property, every other unit must be designated as affordable to households making up to 60 percent the area median income for a 30-year-period after its construction. ADUs will also not be allowed to be used as short-term rentals, such as those rented through Airbnb or Vrbo. 

Once the ordinance becomes effective Wednesday, property owners will be able to punch in their addresses on the city’s ADU website to determine if their building is eligible to add ADUs, and whether other restrictions apply.

The website also includes a flowchart that lays out the new process for getting ADUs approved, which includes a pre-certification process, which is unique from other city development processes. Under that process, an applicant submits preliminary information, such as the property’s address, ownership information, age of the property, number of existing units, number and type of ADUs sought and, if required, an affordability covenant and owner-occupancy documentation in order to get permission to seek a building permit. 

The use of a pre-certification process is meant to ensure that building permits for ADUs are only filed if they are likely to get approved. 

Stern said a forthcoming virtual pre-certification form is designed to prevent an applicant from proceeding if it detects the property would not qualify. 

That saves the user time as much as it saves DOH time from evaluating ineligible applications. 

“One of the purposes of the pre-certification is to be able to provide a thumbs up or thumbs down with a level of information that does not require hiring an architect or engineer to develop plans,” Stern said.

For users that submit pre-certification applications, Stern said the department would aim to turn those around in a week, although an initial rush of applications could delay that for a time.

From there, Stern said the process largely follows existing processes, with applicants next needing to hire an architect or engineer to design the units and prepare code-compliant plans. Then the applicants must apply for building permits with the attached pre-certification approval letter. Once the permit is approved and paid for, applicants can build. After construction, an inspection is required before anyone can live in a unit. 

Update: This article was updated April 1 to reflect a more accurate number of parcels that now allow ADUs provided by the housing department after the department factored in additional data.