This Accessory Dwelling Unit post is part of our ongoing study of Chicago’s defining building forms and the history of our communities written in buildings. Read about Worker Cottages, Chicago Bungalows, Courtyard Apartment Buildings, Residential Hotels, Greystone Flats, Four-Plus-One Apartments, Fire Cottages, and Skyscrapers.
THE CHICAGO COACH HOUSE & ACCESSORY DWELLING UNIT RENAISSANCE IS HERE
The classic Chicago coach house, along with other forms of Accessory Dwelling Units (ADUs), is no longer a pilot idea. It’s policy. Following the success of the initial program, the Chicago City Council voted to expand ADUs and make them a permanent part of the city’s zoning framework. While not every residential area is eligible, the door is now open in far more places.
Coach houses are detached, secondary dwellings built on the same lot as a primary residence. ADUs go by many names, including granny flats, in-law suites, and basement apartments. They can take a range of forms: converted attics or basements, or new, smaller-scale buildings at the rear of a property. What they share is independence with a separate entrance, a kitchen, and a full bath.
For decades, these housing types were largely prohibited. That changed in 2021, when the city introduced a pilot program across five zones (propelled in part by Streets Blog Chicago’s Steven Vance). Now that the ordinance has been made permanent and expanded, ADUs are allowed citywide in many residential districts, subject to zoning, owner-occupancy requirements, and other conditions. Grant programs and financing options remain part of the equation, particularly for homeowners bringing existing units up to code or adding accessible units.
WHERE ADUs ARE CURRENTLY PERMITTED
The original pilot zones, spanning parts of the North, Northwest, West, South, and Southeast sides, served as the testing ground. Today, those areas remain eligible, but the program has broadened. ADUs are now allowed in many residentially zoned areas across Chicago, though not universally. Zoning designations, block-level limits in certain areas, and other restrictions still apply.
Rather than relying solely on the former zone map, the current citywide ADU map is the most accurate tool for determining eligibility on a given property.
BUILDING GRADUAL & AFFORDABLE DENSITY
The intent behind the ordinance remains intact by introducing density incrementally, in a way that works with the existing housing stock. ADUs are still subject to use and ownership requirements; short-term rentals like Airbnb are not permitted, and in many cases, properties must be owner-occupied.
In some areas, particularly those carried over from the pilot program, limits on the number of ADUs per block may still apply. Age requirements for the principal structure and zoning constraints also factor into what can be built and where.
Affordability remains part of the framework. Projects with multiple ADUs may trigger requirements to reserve a portion of units for households earning below certain income thresholds. Financial assistance programs are still available to qualifying homeowners, helping cover costs associated with construction or code compliance.
FROM PILOT TO PERMANENT
What was once a three-year test case is now a standing policy. The Chicago Department of Housing and Department of Planning and Development evaluated the pilot program and used those findings to inform a broader rollout.
The result is a more flexible housing tool that supports multigenerational living, creates new rental income opportunities, and adds density without large-scale redevelopment. It’s not a free-for-all—but it is a meaningful shift in how Chicago allows its neighborhoods to evolve.
COACH HOUSE AND ACCESSORY DWELLING UNIT POSSIBILITIES
ADUs
The expanded ordinance opens a treasure trove of design possibilities around coach houses and ADUs. There is planning for aging in place for yourself or loved ones, providing proximate yet private lodgings for adult children or other relatives, and that is just the tip of the iceberg. ADUs and coach houses can also be used to house an artist or teacher’s studio space, an office for remote workers who crave live/work separation, a practice space for musicians, a live-in nanny or caregiver’s lodgings, a homeschool pod, or just a source of rental income to help pay off a mortgage, fund college, or retirement.
Part of the fun of designing or renovating coach houses and ADUs is that so many have interesting historical design details or layouts baked right in, given their longevity in Chicago’s urban fabric. It’s easy to forget that before cities were designed around cars, they were designed around horse-and-carriage set-ups. The coach house was originally designed to store a coach on the first level and often included living quarters for the coachman above.
Coach Houses
Generally reserved for those of a certain economic status, coach houses were auxiliary structures, usually built at the back of a lot, behind the main house. When cars supplanted the horse-drawn carriage as the primary way to transport people, many coach houses were converted into garages. However, many of them don’t look like your average garage, sporting charming, historic designs that match their accompanying structures. In the late 1950s, fearing that the post-war boom would overly densify the city, the construction of new coach houses, and indeed, all basement/attic residential conversions, was banned, with existing ones grandfathered in with the caveat that no renovations could be executed on them. For a look at historic Chicago Coach houses, the Ask Geoffrey column offers excellent examples.
For new present-day coach houses, though, some design parameters will guide the process. Coach houses must be shorter than 22 feet above grade and smaller than 700 square feet. Additionally, the overall footprint cannot exceed 60% of the rear setback. Equally exciting is the lifting of the ban on more serious renovations to coach houses, which has been in place for over a half-century. This means existing coach houses can be fully renovated to meet the new parameters, perhaps allowing them to become taller and more spacious, and to better meet their owners’ needs in a more modern, customized way.
MODERN COACH HOUSE DESIGN & ADU CASE STUDIES
Now that the coach house and ADU projects have some room to breathe, Chicagoans are rapidly submitting permit applications for them, and moss currently has several projects underway.
Ravenswood ADU: New Construction
As the second phase of this residential renovation, the project shifts its attention to the back of the lot. We are demolishing the existing garage to make way for a new ADU, making the most of the expansive, double-wide lot.
The ADU is positioned to maintain privacy within the backyard while still feeling visually connected to it. Its massing and fenestration are calibrated to reduce overlook and preserve usable open space, creating a relationship between the two structures. Warm-toned stucco clads both the house and the ADU, adding texture and desert vibes. Above, a deep overhang shelters a balcony that extends living space outward and creates a connection to the back yard.
Site analysis diagrams and early schematic sketches mapping sun paths and prevailing winds. These studies informed the ADU’s placement on the lot and calibrated overhang depths to mitigate summer heat gain while preserving daylight.
LINCOLN SQUARE ADU
Lincoln Square ADU is a total rehab with a brand new addition and is classified as an ADU. We’re designing and building a coach house in the client’s backyard on top of an existing garage. The project will add a balcony and overhang that provides shade for residents enjoying the outdoors in the summer while also shielding the interior from the sun’s harsh rays via passive cooling. Since the site is already under construction, connecting services for the new construction are easier.
Below are the ADU renderings and site analysis sketches.
LOGAN SQUARE ADU
The historic carriage house on the lot of the Logan Square coach house, built in original brick and outfitted with a horse stable, is being restored and retrofitted to include a second story. The main, two-unit building will remain untouched. Challenges with this project include structurally supporting the new second story atop the original carriage house, which requires connecting utilities from existing on-site inputs.
Below are the ADU design and site analysis sketches.
EVANSTON ADU
For another project in Evanston, we are tearing down an existing well-worn coach house and building a new one on a different part of the lot. Based on our site analysis, the original coach house is not in an ideal location and would be better suited elsewhere on the property. The new structure, adjacent to the main house, will contain a garage with an Accessory Dwelling Unit built on top.
Below are ADU design and site analysis sketches
