Accessory Dwelling Units (ADUs)
Evanston and 11 Other Municipalities
Cook, Lake, McHenry, Will, and Kane Counties
The City of Evanston’s ADU ordinance enables homeowners to build or convert accessory dwelling units to increase housing supply, provide flexible multigenerational and aging-in-place options, and create affordable rental opportunities while carefully regulating size, design, and lot coverage.
Defining Accessory Dwelling Units
Accessory dwelling units – commonly referred to as “carriage houses,” “coach houses,” or “granny flats,” among other names – are independent housing structures, typically small in size, that sit on the same property as a primary residence. Traced back to 18th century England, where they were originally built by wealthy homeowners to store horse-drawn carriages and provide living quarters for their house-staff, they became popular in the United States throughout the 19th century and were later repurposed into garages following the advent of the automobile. ADUs remained common in American cities until the mid-20th century, when zoning ordinances began prohibiting their construction and implementing minimum parking requirements.
As American cities are once again grappling with a housing supply and affordability crisis, ADUs have been identified as a means by which cities can optimize land-use efficiency and increase housing supply; and many have reversed course on the zoning of ADUs. Beyond their functionality as an efficient use of land, ADUs also provide economic and lifestyle benefits – offering homeowners the potential to generate additional income while also creating flexible and adaptive living environments. This flexibility can enable seniors to age-in-place, allow for comfortable multi-generational living arrangements, or provide affordable living opportunities for renters.
Background
Evanston’s history with ADUs followed the same path as that of other American cities, which left Evanston with a small stock of late 19th and early 20th century coach houses but banned their construction in the mid 20th century and placed strict regulations on existing structures.
Prior to 2018, ADUs in Evanston could only be built behind single family homes and only members of the primary homeowner’s family were permitted to reside in the unit. In 2018, aiming to increase the supply of rental units in Evanston, Evanston City Council unanimously passed an amendment to the City’s zoning code that allowed for the rental of existing ADUs to non-family members. The amendment yielded quick results, as 34 existing Evanston coach houses were registered with the City as rental units that year.
Two years following that amendment came two others, also passed unanimously, with the aim of increasing Evanston’s overall housing supply. The City first passed a temporary ordinance in January 2020, legalizing the construction of ADUs behind any primary structure and on any conforming property. Then, following roughly nine months of planning efforts that included the review of ADU regulations of other cities and guidance from the American Planning Association, the Urban Land Institute, and AARP, the City Council unanimously finalized an amendment to Title 6 of the Evanston City Code that created official ADU regulations and revised the calculation of building lot coverage.
How It Works
The ordinance allows for both the new construction of ADUs and for the conversion of existing detached structures (such as garages) into ADUs. Every residential zoning lot in Evanston is allowed one ADU, attached or detached, as an accessory to any residential building regardless of lot size. An ADU is not to exceed 1,000 square feet, and its height may not exceed 20 feet for flat or mansard roofs and 28 feet for pitched roofs. There are minimal design standards meant to blend ADUs into the existing neighborhood fabric, which limit the location of entrances and exterior stairs to the interior side or rear elevations. The maximum floor area ratio or building lot coverage of the underlying zoning remains the same, but unenclosed parking spaces no longer count toward building lot coverage, and there is no parking requirement for the addition of an ADU. The property owner is not required to live on the property, but the ADU is held in common ownership with the primary building.
Goal
To combat rising housing costs in Evanston by increasing the supply of affordable living options and optimally using available land. ADUs also aim to improve quality of life by providing aging in place and multigenerational living options.
Target
Homeowners and developers in Evanston.
Financing
The construction of a new ADU typically costs between $100,000 and $300,000.
Success
Since the ordinance’s passing in 2020, 14 ADUs have been constructed throughout the City. While most of this development has been attributed to the desire of property owners to age in place, it’s expected that these units will eventually become available in the rental market.
Lessons Learned
Of 44 permits issued for the construction of ADUs, 14 have been built; suggesting that there may be prohibitive financial and/or legal constraints related to the building process. The City is currently in the process of identifying potential barriers in its building code and exploring ways to ease development costs. The primary lesson is that while legalization of ADUs is an important first step, there are further necessary steps that must be taken in order to realize the full potential of ADUs.
Other Regional Examples
In 2017, the Village of Oak Park allowed “coach house” ADUs, which are ADUs above a detached garage. In 2022, the Village expanded this ordinance to allow more types of ADUs, including detached structures or garage conversions. As of July 2025, Oak Park has seen development of 18 ADUs, all of which are coach house ADUs.
Other municipalities that have permitted ADUs include Antioch, Bull Valley, Chicago, Homewood, Lake Bluff, Northbrook, Park Forest, South Elgin, Wilmette, and Woodstock.
Contact Information
City of Evanston Community Development Department, www.cityofevanston.org
This case study was last updated in February 2026.
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