ADU rules in Oak Park

Oak Park allows two forms of detached ADU on any zoning lot used for a single-family dwelling. A coach house occupies the upper floor of a detached garage, above ground-level parking spaces (Section 9.3.B.5), and a ground-floor detached unit may be either a converted parking garage or a new standalone building placed in the rear or side yard (Section 9.3.B.6). Only one ADU is allowed per zoning lot, and new detached units and coach houses cannot exceed the height of the house. The authority is Ordinance 22-1, approved January 10, 2022, which added Section 9.3.B to the 2017 Zoning Ordinance; before that the village had allowed only coach houses. Detached units in one of Oak Park's historic districts or on a landmark property go through Historic Preservation Commission review.

Both attached and interior ADUs are permitted. An attached unit is an addition in the rear or side of the house with its own separate entrance, meeting the same Table 4-1 dimensional standards that apply to the single-family dwelling itself (Section 9.3.B.7). An interior unit is an attic or basement conversion inside the house, which also needs its own separate entrance from the single-family dwelling (Section 9.3.B.8). Section 9.3.A.3 carves attached ADUs with separate entrances out of the general bar on accessory structures in required setbacks. Because Section 9.3.B.2 allows only one ADU per zoning lot, a homeowner picks one form rather than stacking a basement unit under a coach house.

Sections 9.3.B.6.b and 9.3.B.7.b each require a detached or attached unit to be 'less than 1,000 square feet of livable space and/or smaller than the single-family dwelling'. Coach houses above a detached garage and interior attic or basement conversions carry no square-foot cap of their own in the text. Detached forms are still bound by the general accessory-structure limits: all detached accessory structures together may cover no more than 20 percent of the lot, a detached structure's footprint cannot exceed the principal building's footprint, and detached accessory structures are capped at 20 feet in height (Sections 9.3.A.4, 9.3.A.6 and 9.3.A.7). New coach houses and new detached units additionally cannot exceed the height of the single-family dwelling.

Section 9.3.B.1 is a single sentence: 'Either the single-family dwelling or the accessory dwelling unit must be owner-occupied.' The owner may live in either unit and rent the other, but one of the two has to be owner-occupied, and the phrasing is an ongoing condition rather than a test applied only at permit time. Illinois has no statewide ADU statute and nothing preempting local owner-occupancy rules, so this stands unqualified. Oak Park is a home-rule municipality under Illinois Constitution art. VII, sec. 6 (population well above 25,000) and zones under its own home-rule power rather than under 65 ILCS 5/11-13-1.

Section 9.3.B.3 states flatly that 'No additional parking is required for an accessory dwelling unit.' The catch sits on the other side of the ledger: a single-family dwelling needs 2 spaces per unit under the Article 10 parking table, and Section 10.1.A.1 bars reducing existing off-street parking below the requirement, so the village's ADU guide tells owners that if a garage is converted into an ADU any displaced parking required for the house must be accommodated on-site. Section 10.1.B grandfathers existing structures that genuinely lack room for the required parking, subject to Zoning Administrator review and evidence that the property never had it. A coach house avoids the problem by definition, since it sits above ground-level parking spaces.

An ADU is an accessory use regulated in Article 9, not a listed use in the Table 8-1 use matrix, so there is no special-use hearing before the Plan Commission or the Zoning Board of Appeals. The route is a building permit filed through the village's Village View portal; every building-permit application is treated as an application for a certificate of zoning compliance, which the Zoning Administrator issues once the plans are found to comply (Section 14.7.D). The village's ADU guide describes the review as a zoning analysis plus building and fire code review, engineering review and, where applicable, historic review. In a historic district or on a landmark property the Historic Preservation Commission review process applies, and a Certificate of Appropriateness is required where the project demolishes historic material.

Renting the ADU is squarely contemplated: the village's zoning page lists 'a rental unit for extra income' among ADU benefits, and Section 9.3.B.1 only requires that one of the two units be owner-occupied. Long-term rentals of one-to-three-unit properties, single-family homes included, need a Residential Rental License from Neighborhood Services under Village Code chapter 12, article 2, at $10 per rental unit, renewed every other year until the unit is vacant or owner-occupied, with an annual landlord management seminar under section 12-2-12. Short-term rentals are legal but licensed under Village Code chapter 8, article 40 (Ord. 21-54, effective November 1, 2021, enforced from June 1, 2022, amended by Ord. 2022-55 on September 6, 2022): one license per unit, annual renewal, a pre-license inspection, $500,000 of homeowner's or host protection insurance, marketing through a hosting platform, no stay shorter than 24 consecutive hours or longer than 182 days, and occupancy caps by bedroom count. License fees run $100 for an owner-occupied operator and $250 for a non-owner-occupied village resident. The ordinance keeps the ADU on the same zoning lot as the house and says nothing about selling it separately.