Naperville's Zoning Ordinance (Title 6 of the Municipal Code) does not define 'accessory dwelling unit' as a permitted use category. A second self-contained dwelling on a single-family lot is generally allowed only where the underlying district permits two-family or multi-family use (R2 or higher), or where the Planning and Zoning Commission and City Council approve a variance, conditional use, or planned unit development. Illinois has no statewide ADU preemption statute; under the Illinois Municipal Code (65 ILCS 5/) and home-rule authority (Ill. Const. Art. VII Sec. 6), Naperville retains full zoning discretion and has historically applied it strictly.
A Naperville homeowner pursuing a second dwelling unit on a single-family parcel encounters one of the more restrictive regulatory environments among Illinois municipalities. First, the Zoning Ordinance (Title 6) establishes residential districts including R1 (large-lot single-family), R1A, R2 (two-family), R3 and R3A (multi-family), and mixed-use overlays. A second independent dwelling is permitted by right only where the underlying district allows two-family or higher use; on an R1 or R1A lot, the owner must obtain a variance from the Planning and Zoning Commission (Title 6 Chapter 2, Section 6-2-15 Board of Appeals procedures) or proceed through a conditional use or planned unit development. Second, accessory structures are governed by Title 6 zoning provisions for accessory uses incidental to the principal dwelling; this framework has not been interpreted to allow a second fully independent dwelling with its own kitchen, bathroom, and exterior entrance. Third, the Illinois Residential Code (Capital Development Board adoption of the IRC under 71 Ill. Adm. Code 600) governs construction; building permits are issued by Naperville's Transportation, Engineering, and Development (TED) Business Group through the city's Permitting, Plans and Licensing Portal. Fourth, the Illinois Plumbing Code (77 Ill. Adm. Code 890) requires Illinois-licensed plumbers. Fifth, the Illinois Fire Code (Office of the State Fire Marshal adoption of NFPA 1) and the Naperville Fire Department's Community Risk Reduction Division review egress, separation, and smoke/CO alarm coverage. Confirm the parcel's current district designation with Naperville Planning at (630) 420-6694 before designing.
Building a second dwelling without zoning approval or building permits triggers a stop-work order from Naperville TED Business Group, double permit fees on after-the-fact applications, mandatory exposure of concealed framing, plumbing, and mechanicals for inspection, and possible removal orders. Zoning violations are enforceable under Title 6 with daily civil penalties and injunctive relief in the DuPage County Circuit Court (18th Judicial Circuit) or Will County Circuit Court (12th Judicial Circuit) for parcels south of 75th Street. Unpermitted occupancy can void homeowner insurance and disqualify the unit from any future legitimization.
Naperville, IL
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