Building permits, zoning and land rules in Williamson County, Tennessee

Unincorporated Williamson County requires a building permit before locating, erecting, constructing, reconstructing, extending, converting or structurally altering a building or structure, unless an applicable exemption applies; work cannot begin before issuance¹. Necessary water-supply, sewer or septic, storm-water and driveway approvals, plus an approved Zoning Certificate, must precede the building permit¹. Williamson County uses the 2021 building, residential, plumbing and mechanical codes, excluding the residential automatic-sprinkler provision and electrical chapters, and the 2018 energy code with 2009 tables; electrical permits for unincorporated projects come through Tennessee^9,10. A qualifying owner may build one residence for personal use every two years, but not for sale, lease or rent; the contractor-license exemption does not waive local building permits, and anyone hired whose portion costs $25,000 or more still needs the applicable contractor license⁸.

The Williamson County Building Codes Department handles county building-permit applications; reach Building Codes at (615) 790-5718, Info.buildingcodes@williamsoncounty-tn.gov, or 1320 West Main Street, Suite 400, Franklin, TN 37064^11,12. Apply online through the county Electronic Plan Review System and consult the published fee-and-requirements document; building permits and privilege taxes require separate checks¹¹. Construction inspections include footings, foundation, slab, applicable slab plumbing, framing, mechanical and plumbing; each re-inspection costs $50¹³. Electrical permits for unincorporated projects are available separately through Tennessee’s CORE system¹². The Town of Nolensville issues its own building permits; the Town of Smyrna, listed as mainly in Rutherford County and reaching into Williamson County, also issues its own building permits^14,15. For a municipal parcel in Williamson County, ask the county Department of Sewage Disposal Management to confirm septic jurisdiction before applying⁴.

Williamson County zoning governs development in unincorporated areas; Franklin, Brentwood, the Town of Nolensville and the Town of Smyrna, mainly in Rutherford County and reaching into Williamson County, set their own zoning within municipal limits^{2,16,17,18,19}. County regulations require septic construction permits throughout Williamson County; ask the Department of Sewage Disposal Management to confirm the septic authority for a municipal address^3,5. The county’s online zoning ordinance and map are reference materials; the print ordinance and subsequent amendments control discrepancies². Minimum lot area in the A district is 15 acres; RP-5 and RD-5 residential lots in traditional subdivisions require 5 acres¹. MGA-5 residential standards require 5 acres and setbacks of 100 feet front, 20 feet side and 60 feet rear¹. Setbacks can depend on recorded plats and lot history, while height limits vary by district and use¹. Conservation subdivisions require Planning Commission concept-plan approval followed by preliminary and final plats¹. Agricultural subdivisions require a preapplication conference and final plat; created lots must be at least 1 acre and overall density cannot exceed 1 lot per 5 acres²⁰.

Williamson County's Department of Sewage Disposal Management administers individual onsite septic systems and designates the appropriate system type for each property^3,4. A valid construction permit is required before a conventional or alternative septic system is built, altered, extended, modified or repaired⁵. Every installation needs a layout inspection before construction and a final inspection, with additional inspections possible for the soil, trenches or system type⁵. Reach the department at (615) 790-5751, Info.sewagedisposal@williamsoncounty-tn.gov, or 1320 West Main Street, Suite 411, Franklin, TN 37064³. Only about 14% of county soils rate as free of severe limitations for a conventional drain field, so establish wastewater feasibility before fixing the house location²¹. Pit privies and composting toilets require Board of Health approval and a recorded restriction or agreement; a pit privy cannot be the primary disposal method for a building with running water, and privies are limited to parcels over 10.01 acres and parcels without habitable or permanent structures⁵.

Williamson County may issue a Temporary Use Permit for an RV or travel trailer during primary-home construction, after the home’s building permit is issued; approved water and sewage disposal and district setbacks are required⁶. The construction shelter permit lasts one year, with one six-month renewal possible only after permanent construction begins⁶. Temporary RV shelter may also be permitted after fire or natural disaster makes a single-family dwelling uninhabitable⁶. We could not confirm general long-term RV living or private-land camping; ask Williamson County Planning about the parcel and intended duration²². A primary tiny home must qualify as an allowed dwelling use and meet district, building-code and wastewater rules; the dwelling-unit definition excludes RVs^1,7. An accessory dwelling needs an eligible district and Minor Site Plan review¹. Williamson County allows only one accessory dwelling per parcel, limited to 750 square feet or 25% of the principal dwelling, whichever is greater, but never more than 75% of the principal dwelling; a deed restriction must be recorded before zoning and building approval²³. An accessory tiny home classified as a mobile home is allowed only in districts that allow mobile homes²³.

1. Ask Planning to confirm the parcel's jurisdiction, zoning district, permitted dwelling type, setbacks and any subdivision review^2,20,22.
2. Establish wastewater feasibility and obtain the county septic construction permit before system work begins^4,5.
3. Resolve access: lots generally must abut a public road, while access easements and easement-dependent subdivisions have specific standards¹.
4. Apply for a Zoning Certificate before development on property containing a special flood-hazard area²⁴.
5. Submit building and related applications through the Electronic Plan Review System and consult the current county fee materials¹¹.
6. Arrange county building inspections and separate state electrical permitting^12,13.
7. Complete septic inspections; flood-hazard projects also require final elevation documentation before a Certificate of Compliance or Occupancy can issue^1,5.

Before buying undeveloped land in Williamson County, have Planning verify the zoning district, allowed dwelling type, lot size, setbacks, building height and subdivision history^1,2,20,22. Check wastewater capacity early because only about 14% of county soils rate as free of severe limitations for a conventional drain field²¹. Confirm legal access because county rules generally require public-road frontage unless an access-easement exception applies¹. A driveway on state highway right-of-way requires a TDOT entrance permit²⁵. Special flood-hazard areas carry preservation, engineering and development limits beyond ordinary zoning²⁴. We could not confirm a countywide private-well permit rule or general utility-connection rule, so ask Planning and the prospective service provider before closing²².