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

Significant Restrictions

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

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

Key Facts

Default rule: One principal structure per lot
ADU exception added: October 18, 2018 amendment
Zoning status: Table 3-102A: SUP in most districts
Barred in: More intensive residential districts (X)
Standards located in: Appendix B, not the main articles
Applies in: Unincorporated Sullivan County only

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 Sullivan County, TN rules below cover local size, height, and setback requirements.

Summary

Sullivan County generally limits a lot to one principal structure, but Section 3-103.6(5) carves out Accessory Dwelling Units as an exception, added October 18, 2018. Table 3-102A lists 'Accessory Apartment' as a Supplemental-Provisions use requiring Building Commissioner approval in most districts, and bars it outright in the county's more intensive residential districts.

These county ordinances apply to unincorporated areas of Sullivan County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

5. One Principal Building - There shall be no more than one principal structure and its customary and incidental accessory structures on any lot or parcel of land, unless otherwise specifically permitted in this chapter or unless a development plan is approved by the Planning Commission as provided in this chapter. (amended July 21, 2008). Accessory Dwelling Units may be permitted- see Supplemental Regulations in Appendix B for Accessory Dwelling Units (amended October 18, 2018). ... TABLE 3-102A: 'Accessory Apartment (amended 2018) SUP SUP SUP SUP X X'

View official code

Full Breakdown

3, in most of the county's agricultural and residential district groupings, while marking the use 'X,' specifically not permitted, in the remaining district groupings. A related but distinct row, 'Farm Employee Housing,' offers separate SUP-approved living quarters tied specifically to agricultural operations rather than a general accessory dwelling. Because the resolution's main articles point applicants to Appendix B rather than listing the ADU's size, parking or occupancy standards directly, the district use table and the one-principal-building exception are the operative zoning gate, and Appendix B carries the design and operating detail. This structure, like the rest of the resolution, governs unincorporated Sullivan County only.

Violations & Fines

Building or occupying a second dwelling unit on a lot without either an approved Accessory Apartment permit or an approved Planning Commission development plan is a zoning violation of the one-principal-building rule. Section 12-107.2 makes the violation a misdemeanor with a civil penalty up to $500 for each day it continues, and Section 12-107.3 authorizes the Building Commissioner or a damaged adjoining owner to seek an injunction or other court action to correct the violation.

Frequently Asked Questions

Can I add a second dwelling unit, like a garage apartment, on my Sullivan County property?

Only as a permitted Accessory Apartment. Section 3-103.6(5) generally limits a lot to 'one principal structure and its customary and incidental accessory structures,' but the same section carves out an exception: 'Accessory Dwelling Units may be permitted, see Supplemental Regulations in Appendix B for Accessory Dwelling Units,' an exception added October 18, 2018.

Is an accessory apartment allowed in every zoning district?

No. Table 3-102A lists 'Accessory Apartment' as a Supplemental-Provisions use, requiring Building Commissioner sign-off, in most of the county's agricultural and residential district groupings, but marks it 'X,' specifically not permitted, in the remaining district groupings, so eligibility depends on where the lot sits.

Where do I find the actual size or design rules for an accessory dwelling unit?

In Appendix B's Supplemental Regulations for Accessory Dwelling Units, referenced directly by Section 3-103.6(5). The main zoning articles point to that appendix rather than listing the size, parking or occupancy standards themselves, so an applicant needs the appendix, not just the district use table, before designing one.

Sources & Official References

[1]Sullivan County, TN Zoning Resolution (updated 5/9/25)

Other rules in Sullivan County

Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Abandoned VehiclesSignificant Restrictions Parking Rules: Driveway RulesSome Restrictions Landscaping Rules: Tree Removal & Heritage TreesLight Restrictions

All Sullivan County rules

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

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