February 23, 2026
As the first installment of our ongoing series analyzing the legislative components of Governor Pritzker’s proposed housing agenda, the Building Up Illinois Developments (“BUILD”) initiative, this alert focuses on the proposed mandates and restrictions on Accessory Dwelling Units (“ADUs”) included in House Bill 5626, introduced in the Illinois House by Representative Kam Buckner on February 19, 2026. If approved as presented, this legislation will significantly curtail the authority of Illinois municipalities to regulate or restrict ADU developments in residential zoning districts, including coach houses, granny flats, or backyard cottages, and apartment units constructed in garages, attics, and basements.
Importantly, the legislation would preempt home rule authority, preventing all municipalities from adopting or enforcing rules regulating ADUs inconsistent with these standards, marking a significant shift in local control over residential density.
Defining the Accessory Dwelling Unit
The proposed legislation defines an ADU as a residential living unit located on the same lot as a single-family dwelling that provides independent living facilities for sleeping, eating, cooking, and sanitation. The bill specifies that ADUs may be either attached to the primary dwelling or a separate structure.
Prohibited Local Restrictions
The bill explicitly deprives municipalities of the power to curb ADU development through alternative regulatory mechanisms:
- Universal Zoning Review. Municipalities must permit at least one ADU on any property zoned for single-family homes and may not impose additional zoning controls on ADUs that are more stringent than what is required for a single-family home, including, but not limited to, lot size, setbacks, aesthetic requirements, design review requirements, frontages, space limitations, or other zoning requirements. If a property owner adds an ADU while maintaining compliance with the underlying zoning district regulations, the ADU must be permitted by right.
- Parking Obligations. Municipalities cannot require additional off-street parking for properties with ADUs that exceeds parking requirements for a single-family home.
- Familial Occupancy. Municipalities are prohibited from requiring a familial relationship between the occupants of the primary house and occupants of the ADU.
- Unit Size or Bedrooms. Municipalities may not establish minimum or maximum limits on the square footage or the number of bedrooms in an ADU.
- Impact Fee Exemptions. Municipalities authorized to levy fees for schools, parks, utility infrastructure, or transportation may not impose impact fees for the addition of an ADU to a single-family property, even though a new dwelling unit is being added to the property.
Mandatory Authorization and Zoning Requirements
Beginning January 1, 20271, every municipality in Illinois must review and amend its local zoning ordinance, as appropriate, in accordance with the Act:
- Mandatory Allowance of Accessory Dwelling Units. Municipalities must permit at least one ADU on each lot in any zoning district where single-family dwellings are allowed.
- Parity of Regulation. Municipalities must remove any additional requirements related to lot size, setbacks, aesthetic standards, frontage, or space limitations that would prevent ADU development more stringently than is ordinarily required for a single-family dwelling unit.
- Construction Flexibility. ADU development must be permitted as new construction or as a conversion from an existing structure, such as an attached or detached garage, basement, attic, or backyard cottage. Further, property owners must be allowed to construct an ADU concurrent with the principal dwelling unit.
Impact of ADU Mandates on Maxed-Out Lots
Whether an ADU must comply with the underlying zoning and bulk regulations that already apply to a single-family zoning lot is unclear. While the bill prohibits municipalities from imposing regulations that effectively prevent ADU development, there is uncertainty regarding single-family lots that are already “maxed out.” For instance, where a lot has already met the maximum floor area ratio (“FAR”), the maximum number of accessory structures, impervious surface limits, or utility capacity, these underlying zoning regulations may still limit or prevent the development of an ADU. Municipalities will also retain authority to enforce building safety, construction codes, and generally applicable zoning standards.
As the legislative session progresses, this proposed legislation will likely continue to evolve through ongoing review and negotiation. We will continue to monitor developments and keep our clients apprised of changes to the bill and the potential impact on local development controls. In the meantime, please contact Kelsea Neal Nolot or any other Elrod Friedman attorney for additional guidance on ADUs or other components of the BUILD initiative.
1 It is important to note that other provisions of HB 5626 include preemptions of local zoning authority with a delayed effective date of eight months after the effective date of the entire bill. The ADU provisions of HB 5626 are not included in that delay, and would become effective as early as January 1, 2027, if the General Assembly approves HB 5626 during the spring legislative session and Gov. Pritzker promptly signs it into law.