Dearborn Heights, MI Accessory Structures: ADU Rules (2026)

Section 36-141 permits accessory dwellings to give homeowners housing flexibility for relatives or caregivers while preserving each district's single-family character. Subsection (c) governs units accessory to detached single-family homes in the R1 and RM districts: only one accessory dwelling is allowed per parcel, it must sit entirely within the principal residential structure (detached accessory structures such as garages or backyard cottages are expressly prohibited from housing one), and it must have a minimum gross floor area of 350 square feet while not exceeding 30 percent of the principal building's total gross floor area.

Subsection (b) layers on citywide standards: creating or altering an accessory dwelling requires a zoning compliance certificate under Section 36-4 in addition to any building permit, and the planning commission or building official can demand floor plans, elevation drawings, and a plot plan to confirm compliance. An accessory dwelling cannot be added to a structure that already houses two or more families. Design standards in subsection (c)(5) require the unit to stay visually secondary: access is limited to a shared front entrance or a separate side/rear door, and when viewed from the street it must appear that only one household occupies the site.

Parking in subsection (c)(6) requires one additional off-street space beyond what the principal home already needs, and that extra space cannot go in the front yard. A separate track in subsection (d) covers accessory dwellings in the C1, C2, CX, and O commercial and office districts, which must sit above the ground floor, have their own kitchen, bath, and private entrance, and add one off-street parking space per unit. Homeowners in R1 or RM planning a mother-in-law suite should measure the principal home's gross floor area first, since the 30 percent cap, not just the 350-square-foot floor, can be the limiting factor on a smaller house.