Kirkwood, MO Accessory Structures: ADU Rules (2026)

Kirkwood permits accessory dwelling units (ADUs) only as an accessory to a single-family dwelling on a single lot, per § 25-45(b)(1), and only one such unit is allowed on an individual lot under § 25-45(b)(7). An ADU can be built two ways: as an interior apartment inside the principal dwelling, occupying a basement, first, or second story if designed as an integral part of the home and meeting the main residence's setbacks, or as a separate or converted detached structure such as a converted garage, carriage house, or unit above a garage.

A detached ADU must be built to reflect the architectural style, materials, colors, and roof design of the principal dwelling and must meet the setback requirements that apply to principal buildings in the applicable zoning district, a materially stricter standard than the five-foot accessory setback that applies to ordinary sheds. Section 25-45(b)(6) caps ADU height at two stories, and in no case may an ADU exceed the height of the principal building. Section 25-45(b)(8) requires a minimum lot area of 15,000 square feet for any lot containing an ADU, and § 25-45(b)(9) caps the unit's floor area at 750 square feet with no more than two bedrooms, counting basement space toward that cap but excluding garage space when the ADU sits within a detached garage.

Section 25-45(b)(10) requires one additional off-street parking space with direct, drivable street access, on top of whatever § 25-65 already requires, and § 25-45(b)(11) requires the lot owner to live in either the principal dwelling or the ADU as long as both are occupied.