Waukegan, IL Accessory Structures: ADU Rules (2026)

1 permits accessory dwelling units (ADUs) only as a detached structure on a zoning lot already containing a single-unit dwelling, and only in the rear yard. 03-1 requires site plan review ("S") for ADUs in the R1, R2, R3, R4, R5, L1, L2, and L3 districts; the use is not allowed at all in the CR or business/industrial districts. Only one ADU is permitted per zoning lot. The maximum size is 900 square feet, and the ADU counts toward the lot's impervious ground cover calculation along with all other accessory structures and paved surfaces, which together may not exceed 40 percent of the yard.

Design standards require the ADU to read as clearly secondary to the principal dwelling, with exterior materials, siding and trim, window design, roof shape, pitch, and material compatible with the main house; the ADU also may not be larger than the principal structure. When an ADU is added, it counts as an additional dwelling unit for purposes of calculating residential parking requirements under the accessory use standards. 09, separate from any building permit needed for construction.