ADU rules in Naperville

Naperville does not allow a detached backyard ADU. The city has no accessory dwelling unit ordinance at all, and its one codified path to a second dwelling unit on a single-family lot, the residential care unit in section 6-2-34, is expressly barred from taking detached form: the unit 'is prohibited from being built as a stand-alone accessory structure or attached an accessory structure.' Every residence district in Title 6, Chapter 6 permits only one principal dwelling (R1A, for example, lists 'single-family detached dwellings' and 'residential care homes' as its residential permitted uses), and no district lists a detached accessory or second dwelling as a permitted or conditional use. A detached structure in the rear yard is regulated as an accessory building under section 6-2-10, which caps residential accessory structures at 18 feet in height, limits them to the footprint of the principal structure, and allows no dwelling use.

An attached or internal second dwelling unit is possible only as a 'residential care unit,' and only for a narrowly defined occupant. Section 6-2-34.1 permits the unit to 'be attached to a principal dwelling unit so long as the subject property's underlying zoning district requirements are met,' and section 6-2-34.2.3 lets conditional use approval be sought 'in any zoning district where a detached single-family home is a permitted use.' The gate is the occupant, not the construction: section 6-1-6 defines a residential care unit qualifying individual as someone 'screened and determined eligible for services by an independent service coordination agency' whose eligibility 'substantiate[s] that joint occupancy of a residential lot is medically necessary and/or beneficial,' and expressly excludes people with drug, alcohol or other chemical dependency. A general-purpose in-law suite, rental apartment or basement unit for a non-qualifying relative or tenant is therefore not permitted in Naperville.

Section 6-2-34 sets no floor-area limit and no percent-of-primary-dwelling limit on a residential care unit. Instead, section 6-2-34.3.1 requires the unit to 'comply with all Naperville Municipal Code requirements, including the subject lot's underlying zoning district requirements for required yards, height limitations and bulk regulations.' Because the unit must be inside or attached to the principal dwelling, the practical cap is the district envelope: in R1A, for example, buildings are limited to two and one-half stories and 35 feet (section 6-6A-8), with a 30 foot front yard, 8 foot minimum interior side yards and a rear yard of 25 percent of lot depth up to 30 feet (section 6-6A-7). Section 6-2-34.3.2 allows 'only one (1) residential care unit per lot of record unless a variance is obtained,' and section 6-2-34.3.3 limits occupancy to one qualifying individual unless the unit is operated as a residential care home.

Owner occupancy is both an eligibility condition and a continuing obligation. Section 6-2-34.2.1 provides that 'to be eligible for a residential care unit, one of the dwelling units on the residential lot must be occupied by the legal or beneficial owner of the lot.' It is policed annually: section 6-2-34.4.2 requires the owner to file a sworn affidavit with the Zoning Administrator on or before January 31 each year certifying continued compliance, and permits inspection of all dwelling units on the property at the Zoning Administrator's discretion. Section 6-2-34.4.3 revokes the conditional use if the owner 'ceases to occupy the premises or sells or leases their interest in the property to any other person,' unless the city approves a new conditional use or the buyer or tenant independently meets every residential care unit criterion. Illinois has no statewide ADU statute preempting local owner-occupancy rules, so this requirement stands unqualified.

Section 6-2-34.3.6 requires that 'one (1) additional off-street parking space shall be required for each bedroom in the residential care unit,' and that the space comply with the off-street parking facility standards in section 6-9-2. That is additive to the base residential requirement: the Parking Class No. 1 schedule in section 6-9-3.1 requires 2 parking spaces per dwelling unit for a single-family detached dwelling. Section 6-9-2.4.2.1 further requires that at least one space per dwelling unit sit in an enclosed garage behind the front and corner side yard line, and bars parking facilities from the required front or corner side yard apart from a narrowly conditioned auxiliary space. A two-bedroom residential care unit therefore adds two spaces to the site's requirement. PA 104-0457, Art. 5 (People Over Parking Act), effective 6-1-2026, bars any unit of local government from imposing or enforcing minimum automobile parking requirements on a development project (a permit to construct or reconstruct a dwelling qualifies) within one-half mile of a public transportation hub (any rail transit station, or an intersection of 2 or more bus routes with combined 15-minute peak frequency) or one-eighth mile of a 15-minute-peak bus corridor, binds home-rule units (Section 5-90), and grandfathers site plans approved before the effective date (Section 5-15(b)). Naperville contains Metra rail stations (Naperville, and Route 59 on the Aurora boundary), which are rail transit stations under the act, so the half-mile hub zone covers part of the city; within it the per-bedroom minimum cannot be imposed on new residential care unit construction. Parcel-level mapping was not attempted, and whether any bus street meets the 15-minute tests was not verified.

There is no administrative or ministerial route. Section 6-2-34.3 states that a residential care unit, 'whether it houses one residential care unit qualifying individual or is used as a residential care home for residential care unit qualifying individuals, is subject to conditional use approval.' Conditional uses run through the procedures in section 6-3-8 and Title 6, Chapter 4, meaning a Planning and Zoning Commission public hearing and City Council action. The applicant carries an evidentiary burden under section 6-2-34.2.2: petitioners 'have the burden of proving that the intended user of the residential care unit qualifies as a residential care unit qualifying individual.' Section 6-2-34.4.1 also requires floor plans, elevation drawings and reconversion plans to be submitted and approved at the time of conditional use approval. Petitions are filed as a Development Petition through the city's Civic Access portal after a required concept meeting with staff.

A residential care unit cannot be rented out on the open market. Section 6-2-34.3.3 limits it to housing 'one (1) residential care unit qualifying individual, unless it is a residential care home for residential care unit qualifying individuals,' and section 6-1-6 restricts that status to someone screened and found eligible by an independent service coordination agency for whom joint occupancy is medically necessary or beneficial. Section 6-2-34.4.3 revokes the approval if the owner leases their interest in the property to anyone who does not meet those criteria. Separately, Title 3, Chapter 18 prohibits short-term rentals throughout Naperville: section 3-18-3.1 makes it unlawful to 'operate, use, offer for rent or use, or advertise for rent or use, any property within the City of Naperville as a short-term residential rental,' defined in section 3-18-1 as a residential structure 'offered for rent for a period which does not exceed thirty (30) consecutive days.' Violations draw fines of 1,000 dollars for a first offense and 2,500 dollars thereafter, per day.