Oakland County, MI Accessory Structures: ADU Rules (2026)

Because Oakland County's 62 municipalities each have independent zoning authority, ADU rules vary block-to-block. Pontiac Zoning Ordinance §2.505 (One and Two Family Dwelling Unit Structures) states that 'only one dwelling unit structure shall occupy a lot or site condominium unit,' a provision that prevents standalone ADUs in most R districts unless the city's two-family standards are used. Royal Oak's Chapter 770 (Zoning) similarly restricts most accessory buildings from being 'used for human habitation' — see §770-22 (Accessory Buildings) and §770-34 (One-Family Residential). Farmington (in Oakland County) and Birmingham have moved in the opposite direction and adopted express ADU provisions tied to lot frontage, max ADU floor area (commonly 600–800 sq ft), owner-occupancy of the principal dwelling, and one off-street parking space per ADU. Property owners must apply to the city's zoning division and pursue a building permit reviewed against the Michigan Residential Code. Mother-in-law suites attached to the principal dwelling and sharing utilities are typically permitted as part of the main house and do not count as an ADU.