Hamilton County, TN Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Hamilton County, TN, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Governing section
- §308 Definitions
- Adopted
- Resolution No. 924-23, Sept. 18, 2024
- Attached garage conversion
- Counts as attached ADU
- Detached garage conversion
- Counts as detached ADU
- Entrance rule
- Cannot be through a garage door
- Size cap
- 800 square feet, same as new build
Summary
Hamilton County lets homeowners legally convert an existing garage into an accessory dwelling unit under Resolution No. 924-23. Section 308 defines both attached and detached ADUs to include converted garage space, but the resulting unit must still meet the same 800-square-foot cap, permanent-foundation, and separate-entrance standards as new construction.
308 - Definitions 1) Attached Accessory Dwelling Unit: An additional subordinate dwelling unit located on the same lot as a principal dwelling unit which is joined to another dwelling at one (1) or more sides by a wall and contained entirely within the footprint of the principal dwelling unit. Examples include converted living space, attached garages, basements or attics; additions; or a combination thereof. 2) Detached Accessory Dwelling Unit: An additional subordinate dwelling unit located on the same lot as a principal dwelling unit and is a stand-alone, separate structure. This can include an existing garage or other accessory structure detached from the principal dwelling unit that is legally converted (fully or partially) to an accessory dwelling unit.
Full Breakdown
Section 308's definitions make garage conversions an explicit, named path to an ADU rather than a gray area. An attached ADU is defined to include 'converted living space, attached garages, basements or attics; additions; or a combination thereof' joined to the principal dwelling by a shared wall and contained within its footprint. ' Section 303 confirms ADUs 'may occupy conforming existing accessory structures,' which covers a stand-alone garage already on the lot. A converted garage is still held to Section 306's numeric standards: the finished ADU cannot exceed 800 gross square feet measured to the exterior walls, counting any conditioned sleeping loft or stairwell, and a detached conversion is capped at 24 feet or two stories.
Section 306(12) requires the converted unit to have a permanent foundation, bars shipping containers and recreational vehicles from qualifying at all, and requires a separate entrance on the side or rear yard; the entrance rule specifically states the separate entrance 'cannot be through a garage,' so a converted garage cannot rely on its old garage door as the ADU's own doorway. Section 304's ownership and occupancy rules apply equally to a converted garage: it must stay under the same owner as the principal home, and the owner must occupy one of the two units. Section 305's short-term-rental ban and Section 306(3)'s side- or rear-yard placement rule for detached units also apply without modification to a converted garage.
Violations & Fines
A garage conversion that exceeds 800 square feet, keeps the old garage door as its only entrance, lacks a permanent foundation, or is rented short-term is not a lawful ADU under Resolution No. 924-23. The Hamilton County Building Inspections Office can deny or revoke the permit and require the space be restored to garage use or brought into compliance with Section 306's standards.
Frequently Asked Questions
Can I turn my detached garage into an accessory dwelling unit?
If I convert my attached garage, does the entrance have to change?
Do converted garages have the same ownership and rental limits as new ADUs?
Sources & Official References
Other rules in Hamilton County
Compare Hamilton County to another location·View the Tennessee accessory structures overview
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