Highland Park, IL Accessory Structures: Garage Conversions (2026)

Highland Park regulates accessory buildings — including detached garages — through Chapter 150 of the City Code (Zoning Code), with bulk and density standards set out in Article VII (Section 150.703 and adjacent sections). A detached garage on a single-family lot is treated as an accessory structure: it cannot exceed the percentage of rear-yard coverage allowed for the underlying zoning district, and an absolute square-footage cap (commonly 1,000 sq ft) further limits combined accessory floor area. Detached garages must be placed behind the principal building line, observe the side and rear-yard setbacks established for the district, and may not be used as a separate dwelling unit without a full ADU approval. Building permits are issued by the Highland Park Community Development Department under Chapter 170 (Building Code), which adopts the 2018 IBC and IRC with city amendments. Electrical, plumbing, and mechanical work all require sub-permits and inspection. Garage-to-living-space conversions require a change-of-use permit, must meet IRC habitable-space rules (egress, ventilation, ceiling height, smoke and CO alarms), and may need a zoning variance if they eliminate required off-street parking.