Sumner County, TN Accessory Structures: Garage Conversions (2026)
Garage conversion rules in Sumner County, TN, sometimes called garage-to-ADU or accessory living unit conversions, govern permits, ceiling height, egress, and parking replacement.
Key Facts
- Permit
- Required, change of occupancy
- Code
- 2021 ICC residential code
- Alarms
- Smoke and CO required
- Second Unit
- Must meet Sec. 1101(R) ADU
- Parking
- Replacement may be needed
Summary
Converting a garage into living space in unincorporated Sumner County means a building permit under the adopted 2021 residential code. If the conversion creates a second dwelling, it must meet the county's ADU rules in Section 1101(R), including owner-occupancy.
Detached ADUs may be established within an existing, legally established accessory structure which meets the current adopted building code for residential structures in Sumner County.
iii. The size of the dwelling unit will be subject to the square footage limitations for accessory structures listed in the table found in this Chapter and such unit shall in no case exceed the size of the principal
124 structure. An ADU must however, provide the minimum area requirement of 300 square feet.
iv. 20,000 square feet of land area is required if connected to public sewer. 40,000 square feet of land area is required if utilizing a septic system.
c. Agricultural employee housing shall only be required to comply with all standards of this section deemed applicable by the County.
4. ADUs Requiring a Special Exception
a. Special Exception Required.
Applications for an ADU requiring a Special Exception from the Board of Zoning Appeals are listed as follows:
i. The Design and Occupancy Standards and Particular
Standards for By-Right ADUs contained in this Chapter
cannot be met.
ii. Applications for an ADU involving a mobile home.
Full Breakdown
Turning a garage into a habitable room changes its occupancy, so Sumner County Building & Codes (615) 452-1467 requires a building permit under the 2021 ICC residential code adopted in 2023. Expect requirements for egress, ceiling height, insulation, and interconnected smoke and carbon-monoxide alarms, with electrical work handled through your electrical provider. If the converted space becomes a separate dwelling rather than added living area, it is an accessory dwelling unit: the Zoning Resolution lets a detached ADU sit in an existing accessory structure that meets the current residential code, but the owner-occupancy, size, and recorded-covenant rules of Section 1101(R) apply. Lost covered parking can affect zoning compliance.
Violations & Fines
Converting a garage to habitable or rentable space without a permit is unlawful construction, subject to a stop-work order and retroactive permitting. A hidden second unit that skips the ADU covenant is a zoning violation.
Frequently Asked Questions
Do I need a permit to convert my garage?
Can the converted garage become a rental apartment?
Sources & Official References
Other rules in Sumner County
Compare Sumner County to another location·View the Tennessee accessory structures overview
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