Elmhurst, IL Accessory Structures: Garage Conversions (2026)

Garage projects in unincorporated DuPage County fall under the DuPage County Zoning Ordinance, Chapter 37, Sec. 37-701 (R-1), 37-702 (R-2), 37-703 (R-3), and 37-704 (R-4). Construction of a new detached garage, replacement of an existing one, or conversion of an attached garage to habitable living space all require a building permit from the DuPage County Building & Zoning Department, applied for through the Accela Citizen Access portal. Detached garages are treated as detached accessory buildings and share the same size envelope as sheds: up to 1,000 sq. ft. on lots of 40,000 sq. ft. or less (plus a 200 sq. ft. bonus where no attached garage remains), or up to 0.025 × lot area (max 2,600 sq. ft.) on larger lots, also plus the 200 sq. ft. bonus when there is no attached garage. Setbacks in R-1 are 40 ft front, 3 ft rear, 40 ft corner side, and 20 ft interior side; R-2, R-3, R-4 use 30 ft front, 3 ft rear, 30 ft corner side, and 10% of lot width or 10 ft (whichever is less) interior side, dropping to 3 ft on lots of 20,000 sq. ft. or less. Maximum height is 15 ft on lots under 40,000 sq. ft. and 24 ft on larger lots. Converting an existing attached garage to habitable space is a structural and occupancy change governed by the County's adopted Building Code and requires plans showing wall, ceiling, and electrical detail. Construction plans must show a minimum 90 mph wind rating, ½" CDX plywood sheathing, treated sill plate with ½" × 10" anchor bolts at 8 ft on center maximum, and a 4" thickened slab where required. Walls within 10 ft of the principal structure must be fire-rated with 5/8" drywall, and the entire ceiling needs attic access when the structure is closer than 10 ft.