CHICAGO BUILDING TYPES: Accessory Dwelling Unit (ADU)


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 CottagesChicago BungalowsCourtyard Apartment BuildingsResidential HotelsGreystone FlatsFour-Plus-One ApartmentsFire Cottages, and Skyscrapers.  


The classic Chicago coach house, along with many other iterations of the Accessory Dwelling Unit (ADU), is about to have a renaissance due to the City’s recent ordinance and pilot project encouraging residents to build new ones and make existing ones code-compliant so that they can return to the rental market.

Coach houses are detached, secondary dwellings built on the same property as the main residence. ADUs go by a myriad of colloquial names, from “granny flats” to “mother-in-law suites” to “coach houses.” They are typically a basement or attic converted into a separate dwelling with a private entrance, full bath, and kitchenette or full kitchen. Still, they also include smaller-scale new buildings built out for a resident separate from the existing main dwelling. These residential types have a very interesting history, which is covered later in this article, but first, the exciting news about coach houses and ADUs: you are about to see a whole lot more of them!

Typical coach house built above garage units

Repealing a 64-year-ban on the typology, the Additional Substitute Dwelling (ADU) ordinance (propelled in part by Streets Blog Chicago’s Steven Vance) will permit the building of ADUs and coach houses in five designated pilot zones spread across north, northwest, west, south, and southeast areas of Chicago. There will be an accompanying grant program targeted at helping lower-to-moderate-income households make existing ADUs become code-compliant. Additional funding will be offered if the ADU becomes accessible.


  • North zone covers parts of the West Ridge, Edgewater, Uptown, Lake View, North Center, and Lincoln Square community areas
  • Northwest zone covers parts of the Albany Park, Irving Park, Avondale, Hermosa, Logan Square, West Town, Near West Side, and East Garfield Park community areas
  • West zone covers parts of the East Garfield Park, West Garfield Park, North Lawndale, and South Lawndale (Little Village) community areas
  • South zone covers parts of the Ashburn, Auburn Gresham, West Lawn, Chicago Lawn, Washington Heights, Roseland, Chatham, Greater Grand Crossing, Englewood, West Englewood, Washington Park, and Woodlawn community areas
  • Southeast zone covers parts of the South Chicago, East Side, South Deering, and Hegewisch community areas

The reasons behind the ordinance, which went into effect in May of 2021, include helping provide a rental income source to homeowners to pay down mortgages and deal with rising property taxes and supporting multigenerational families and/or families navigating aging in place while encouraging a gradual building of affordable density in some of Chicago’s housing shortage-begotten neighborhoods.


The emphasis is on “gradual” density because the West, South, and Southeast pilot zones will be limited to two ADU permits per block. Additionally, secondary properties cannot be listed on Airbnb or similar websites, and eligible properties must be owner-occupied. This will likely keep rental income streams from the ADUs hyperlocal and fund homeowner’s mortgages rather than going toward developers. Other stipulations include that new ADUs can only be built on homes at least 20 years old and must be built in areas zoned for multifamily residences.

Since the impetus behind the ordinance is partially to support lower-income residents, several affordability measures are built in, such as that for properties building two or more ADUs, half of the units must be reserved for Chicagoans earning no more than 60% of the zone’s median income. Additionally, for households earning no more than 80% of the area’s median income, loans of up to $25,000 will be made available for new coach houses or to restore existing ones. 

What comes after the pilot project concludes? After three years, the Chicago Department of Housing (DOH) and the Department of Planning and Development (DPD) will analyze the results, and the ordinance will have a pathway to become citywide.



The new 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 proximal, but still 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 for the storage of 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 constructed on 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. Still, many don’t look like your average garage, sporting charming historical designs that match their accompanying structure. 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 were banned, with existing ones grandfathered in with the caveat that no renovations could be executed on them. For a look at some historic Chicago Coach houses, the Ask Geoffrey column has some excellent examples.

However, some design parameters will guide the process for new present-day coach houses. Coach houses must be shorter than 22 feet above grade and smaller than 700 square feet. The overall footprint cannot exceed 60% of the rear setback. Equally exciting is lifting 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 renovated fully to meet the new parameters, perhaps allowing them to become taller and more spacious, as well as meeting the needs of their owners in a more modern and customized way. 


Now that coach house and ADU projects have been given some room to breathe, Chicagoans are rapidly submitting permit applications, and moss currently has three underway.


Lincoln Square ADU is a total rehab with a brand new addition that will be classed 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 is easier. 

Below are the ADU renderings and site analysis sketches.


The historic carriage house on the lot of the Logan Square coach house, built-in original brick and outfitted with a horse stable, will be restored and retrofitted to have 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 the connection of utilities from existing on-site inputs.

Below are the ADU design and site analysis sketches.


For another project in Evanston, an existing well-worn coach house will be torn down and built up brand new on a different part of the lot. Based on our site analysis, the original coach house was not in an ideal location and was better suited to be elsewhere on the property. The new structure, adjacent to the main house, will contain a garage with an ADU built on top of it. 

Below are ADU design and site analysis sketches

  • site plan

DISCLAIMER: Please note that any ads you see on this blog are placed here by WordPress[dot]com. The Administrators of this blog have no connection to or financial interest in any of the promoted products and gain no income from any advertising displayed on this blog.