Arlington Heights, IL Accessory Structures: ADU Rules (2026)

The Village of Arlington Heights zoning ordinance does not broadly authorize accessory dwelling units such as in-law suites, granny flats, or backyard cottages as permitted uses in standard residential districts (R-1 through R-5). Each residential lot is generally limited to one principal dwelling unit. Converting a garage, basement, or detached structure into a separate dwelling unit is not allowed without zoning relief. Property owners seeking to create a secondary dwelling unit would need to pursue a special use permit or a planned development amendment, both of which require application to the Village Planning Commission and approval by the Village Board. Public hearings with neighbor notification are part of the process. Illinois does not have a statewide ADU mandate similar to California or Oregon, so municipalities retain full authority over whether to allow ADUs. Arlington Heights has not adopted ADU-specific enabling legislation as of the current code. Homeowners may create accessory living spaces (such as a finished basement suite) that do not have a separate entrance, kitchen, or address, as these are not considered separate dwelling units under the zoning code. Any habitable space must comply with building code requirements for egress, ceiling height, ventilation, and fire safety.