Hamilton County, TN Accessory Structures: ADU Rules (2026)

Resolution No. 924-23 inserted a new Section 300, Accessory Dwelling Units, into Article V of the Hamilton County Zoning Regulations. Section 302 lets ADUs attach or stand alone in any zone that permits single-family detached dwellings, but excludes the A-1 Agricultural District outright, and Section 302(3) limits ADUs to lots served by public sanitary sewer; a septic-served lot cannot add one. Section 306 sets the physical envelope: a detached ADU is capped at 24 feet or two stories and cannot exceed the height of the principal house if that house is shorter, while an attached ADU must stay within the zone district's height limit for the main structure.

Size is capped at 800 gross square feet, measured to the exterior walls and counting any conditioned sleeping loft or interior stairwell; a secondary unit larger than 800 square feet is reclassified as a second dwelling unit under Section 104 and no longer qualifies as an ADU. Detached units must sit in the side or rear yard, never the front, with setbacks of 40 feet from the primary street, 10 feet from a side or rear street, and 5 feet from a common side or rear lot line.

Only one ADU is allowed per lot, and no minimum on-site parking is required for it, though parking serving the principal dwelling must be preserved. Section 306(12) bars shipping containers and recreational vehicles as ADUs, requires a permanent foundation, and requires a separate entrance on the side or rear that cannot run through a garage. Section 307 lets pre-2024 non-conforming ADUs continue if brought up to current building, fire and life-safety code as required by the Hamilton County Building Inspections Office.