Ann Arbor, MI Accessory Structures: ADU Permits (2026)

Ann Arbor was one of the first Michigan cities to legalize ADUs by-right. Ordinance 16-13, adopted by City Council in 2016, amended what is now UDC Section 5.16.4 (Accessory Dwelling Units) to allow ADUs as a permitted accessory use on any lot in an R1, R2A, R2B, R3, or R4 district containing a one-family or two-family dwelling. The 2021 Unified Development Code consolidation moved the standards into UDC Chapter 5. Core standards: an ADU may be attached, internal, or detached; floor area is generally capped at 800 sq ft or 60 percent of the principal dwelling, whichever is less; height is limited to the underlying accessory-structure standard (typically 14-25 ft depending on form); one additional off-street parking space may be required unless waived in TC1 or near transit; setbacks follow the underlying district. Permits route through the Ann Arbor Building Department for building, electrical, mechanical, and plumbing trade permits, with plan review under the Michigan Residential Code adopted statewide via the Stille-DeRossett-Hale Single State Construction Code Act (PA 230 of 1972, MCL 125.1501 et seq.). Historic District Commission review applies in the Old West Side, Old Fourth Ward, Division Street, and other Local Historic Districts under Ann Arbor City Code Chapter 103.