Cincinnati, OH Accessory Structures: ADU Permits (2026)

Cincinnati Municipal Code Chapter 1400 (Cincinnati Zoning Code) regulates ADUs as accessory uses. ADUs are permitted in SF-2, SF-4, RM-0.7, RM-1.2, RM-2.0, and RMX residential districts subject to compliance with the underlying district standards and accessory use requirements in CMC Chapter 1417. Maximum ADU floor area is typically 800 sq ft or 35% of principal dwelling, whichever is less. Setbacks follow underlying district accessory structure standards (typically 5 feet from side and rear lot lines). Maximum height generally matches accessory structures - 15-20 feet depending on district. Required permits: zoning compliance review, building permit, plumbing permit (Ohio-licensed plumber), electrical permit (Cincinnati-licensed electrical contractor), and mechanical permit. Permits file through Cincinnati's DBI Online Portal. Properties in Cincinnati's many local historic districts (Over-the-Rhine, Mount Adams, East Walnut Hills, Mount Auburn, Prospect Hill, and others designated under CMC Chapter 1435) require Historic Conservation Board approval prior to permit issuance. Ohio has no statewide ADU preemption law - municipal zoning controls.