Downers Grove, IL Accessory Structures: Garage Conversions (2026)

Downers Grove governs detached garages and other accessory buildings through the Village Zoning Ordinance (Title 5, Chapter 4 — Bulk Regulations and Chapter 11 — Accessory Structures). In single-family residential districts, total building coverage (the principal house, any attached garage, plus all accessory buildings) cannot exceed 32 percent of the lot area. The combined size of all accessory structures on a residential lot is limited to the lesser of 1,000 square feet or the floor area of the principal dwelling. Accessory structures may not exceed 23 feet to the highest point, and they must observe side and rear setbacks of at least 6 feet; an accessory structure placed outside the principal building's setback envelope must also be at least 10 feet from the house. A bonus applies for small detached garages on narrow lots: garages of 500 square feet or less on lots 60 feet wide or narrower are excluded from the 32% coverage calculation. Building permits are issued by the Village Community Development Department. Garage-to-living-space conversions require a change-of-use review, IRC compliance for habitable rooms (egress, ventilation, ceiling height, smoke and CO alarms), and replacement of any required off-street parking displaced by the conversion.