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

Significant Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Knox County, TN, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

RAE zone: one house per lot; no garage apartments
RA zone: garage apartment needs use-on-review approval
RA rear setback: 10 feet from rear lot line
Minimum lot area (sewered): 12,000 sq. ft. (§ 5.11.09.D)
Minimum lot area (unsewered): 20,000 sq. ft. (§ 5.11.09.F)
Daily civil penalty: $10.00 to $500.00 per day
Appeal body: Knox County Board of Zoning Appeals

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Tennessee under recent ADU streamlining laws. The Knox County, TN rules below cover local size, height, and setback requirements.

Summary

Knox County's own zoning ordinance defines a garage apartment as a dwelling unit built above a private garage, but whether you can build one depends on your zone. The RAE Exclusive Residential zone caps every lot at one house and excludes garage apartments entirely; the RA Low Density zone allows one only with Planning Commission use-on-review approval.

City-specific rules exist: Knoxville has its own adu rules rules that differ from Knox County's county-level regulations. If you live in Knoxville, check the city-specific page instead.

5.10.10. Intensity of use. A.Not more than one (1) house shall be permitted on any lot.B.For each dwelling, and buildings accessory thereto, served by a sanitary sewer system there shall be a lot area of not less than ten thousand (10,000) square feet.C.For each dwelling and buildings accessory thereto, not served by a sanitary sewer system, there shall be a minimum lot area of twenty thousand (20,000) square feet; however, a greater lot area may be required based on recommendations by the county health department.D.For those dwellings and buildings accessory thereto not served by a public water supply a minimum lot area as prescribed in the Knoxville-Knox County Minimum Subdivision Regulations, shall be provided.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 23).

Full Breakdown

20). What happens next depends entirely on which residential district applies under Article 5, Zone Regulations, of the county's own zoning ordinance, administered separately from the City of Knoxville's code even though the Knoxville-Knox County Planning Commission reviews applications for both governments. 03), so an accessory dwelling above a garage cannot be built there under any process. A lists "Garage apartments" among the district's "uses permitted on review," meaning the Planning Commission must approve each one individually before a building permit issues, it is never a by-right addition.

B requires that "a garage apartment may be located in the rear yard of houses, but shall not be closer than ten (10) feet to the rear lot line," a shorter setback than the 25-foot rear yard required for an ordinary main building in that zone. F. Property owners in other residential districts, several of which carry their own garage-apartment listings, should check that specific district's uses-permitted-on-review section and area regulations rather than assume the RA standards apply county-wide.

Violations & Fines

Building or occupying a garage apartment without the required use-on-review approval, or violating its approved setback or lot-area conditions, is enforced by the county's Department of Code Administration and Enforcement under § 6.20.02.A, which sets a civil penalty of not less than $10.00 nor more than $500.00, with each day of the violation charged as a separate offense. A cited owner may appeal the determination or penalty to the Knox County Board of Zoning Appeals under § 6.60.05.

Frequently Asked Questions

Can I add a garage apartment to my house in unincorporated Knox County?

It depends on your zoning district. In the RAE Exclusive Residential zone, § 5.10.10.A limits each lot to one house and garage apartments do not appear on that zone's permitted-use lists, so they are not allowed there under any process.

Does the RA zone allow garage apartments outright?

No, not by right. Section 5.11.03.A lists garage apartments as a "use permitted on review," which means the Knoxville-Knox County Planning Commission must approve each application individually before a building permit can be issued.

How far must a garage apartment sit from my rear property line?

In the RA zone, § 5.11.07.B requires at least ten feet of separation from the rear lot line for an approved garage apartment, shorter than the 25-foot rear yard required for the main house in that same district.

Does my lot need to be a certain size to add a garage apartment?

Yes. Section 5.11.09.D requires at least 12,000 square feet of lot area when the lot is served by a sanitary sewer, and § 5.11.09.F raises that minimum to 20,000 square feet if the lot has no sewer service.

What happens if I build a garage apartment without approval?

The Department of Code Administration and Enforcement can assess a civil penalty of $10.00 to $500.00 per day under § 6.20.02.A, treating each day of the unapproved use as a separate violation, and the owner can appeal any citation to the Board of Zoning Appeals under § 6.60.05.

Sources & Official References

[1]Knox County Zoning Ordinance, Art. 5 (Zone Regulations) and Art. 6 (Administration)

Other rules in Knox County

Parking Rules: Overnight ParkingSome Restrictions Parking Rules: Street Parking LimitsSome Restrictions Noise Ordinances: Quiet HoursSome Restrictions Shed & Carport RulesSome Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Noise Ordinances: Vehicle NoiseSome Restrictions

All Knox County rules

How Knox County compares: Easiest Cities to Build an ADU·Compare Knox County to another location·View the Tennessee accessory structures overview

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ADU Rules in Cities Across Knox County

Knoxville, TN