A finished barndominium at dusk with warm interior lighting glowing through its large windows.
Williamson County 2018 IRC with Tennessee amendments

Barndominium Builders in Williamson County, TN

Williamson County is the wealthiest county in Tennessee and the one most people assume is hostile to a metal-clad house. Its zoning ordinance restricts exterior metal siding in exactly one place, the use-specific standards for craft distilleries, and sets no minimum floor area, no roof pitch and no height cap on a dwelling in its rural districts. The real constraints are land and money: RP-5 west of I-65 and RD-5 east of it both take a single-family house by right, on five acres, behind a hundred-foot front setback.

Williamson County at a glance

County
Williamson County
Population
272,061
ZIP codes
37069, 37064, 37067, 37027, 37135, 37179, 37046, 37014, 37062, 37174
Site visits
Our office is on Fieldstone Parkway in Franklin, a few minutes from the county Building Codes Division on West Main Street
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Building conditions in Williamson County

What actually changes from one Tennessee jurisdiction to the next: who issues the permit, whether the residential code is enforced there at all, what the structure has to be engineered to, and what the ground is like. These are the numbers your drawings have to satisfy.

Build conditions for Williamson County , Tennessee: design wind speed Confirmed per parcel. BUILD CONDITIONS WILLIAMSON COUNTY, TNMiddle TennesseeCRITERIA SET LOCALLY DESIGN WIND SPEED Confirmed per parcelWilliamson County publishes no filled-in Table R301.2(1). Tennessee leaves ultimate design wind…ZONING · RP-5 AND RD-5 (RURAL PRESERVATION AND…5-acre minimumRP-5 covers land west of I-65 and RD-5 covers land east of it. Both…EDUCATION IMPACT FEE$3,374 to $12,237 by house size…Charged on the issuance of a new residential building permit, on top…WHO ISSUES THE PERMITWilliamson County Building Codes…1320 West Main Street, Suite 400, Franklin — unincorporated county onlyDesign criteria are filled in by the jurisdiction under Table R301.2 and are confirmed per parcel before any drawing is sealed.
Build conditions for Williamson County, drawn from the sourced facts on this page. Every figure above is cited in the quick-facts panel below, with its source and vintage.
Who permits and inspects
The Williamson County Building Codes Division at 1320 West Main Street, Suite 400 in Franklin, on (615) 790-5718, permits and inspects the unincorporated county. Land inside Franklin, Brentwood, Spring Hill, Nolensville, Fairview or Thompson's Station is permitted by that municipality instead. Electrical permits are the one exception: since June 2023 they go through the State of Tennessee at core.tn.gov rather than the county.

Williamson County Building Codes, williamsoncounty-tn.gov/100/Building-Codes, fetched 31 Aug 2026

Every jurisdiction here enforces a code
The State Fire Marshal's Office lists Williamson County as EXEMPT, its term for a local government that runs its own building department in place of the state residential programme. Brentwood, Fairview, Franklin, Nolensville, Spring Hill and Thompson's Station are all listed EXEMPT too. No part of the county has passed an opt-out resolution, which is unusual in Tennessee: the same list carries 86 opt-out jurisdictions statewide.

Tennessee State Fire Marshal's Office, Residential Jurisdictions & Inspectors, accurate as of 21 Aug 2026, tn.gov, fetched 31 Aug 2026

Codes enforced
The 2021 International Residential Code, effective 30 September 2024, alongside the 2021 IBC, IPC and IMC and the 2018 energy code using the 2009 tables. That puts Williamson a full edition ahead of the statewide residential code, which is still the 2018 IRC. The county excludes IRC Section B 313.2 on automatic fire sprinklers in one- and two-family dwellings, and Chapters 34 to 43 on electrical work.

Williamson County Adopted Codes, williamsoncounty-tn.gov/104/Adopted-Codes, fetched 31 Aug 2026

The metal siding rule, and what it actually covers
The only sentence in the 436-page Williamson County Zoning Ordinance barring metal siding sits in Section 11.03, in the use-specific standards for craft distilleries: exterior building materials shall not consist of metal siding or smooth-finished concrete block, and roofs shall have a minimum pitch of 4:12. It sits among a 25-acre site minimum, a 5,000-barrel storage cap and Alcoholic Beverage Commission licensing. Nothing in the ordinance restricts the cladding on a single-family dwelling, and the mobile-home chapter does not either.

Williamson County Zoning Ordinance, adopted 14 May 2012, revision dated 10 June 2025, Article 11 Section 11.03(A)(10), fetched 31 Aug 2026

Zoning district and minimum lot
RP-5, Rural Preservation District-5, covers land west of I-65; RD-5, Rural Development District-5, covers land east of it. Both carry a 5-acre minimum lot in a traditional subdivision, a density cap of one unit per five acres, 200 ft minimum lot width, and setbacks of 100 ft front, 25 ft side and 50 ft rear. Both list Maximum Height as Not Applicable. A single-family dwelling on a parcel of record is permitted by right in every rural district in the county.

Williamson County Zoning Ordinance Tables 10.02-2 and 10.02-3 and Table 11.01-1, revision dated 10 June 2025, fetched 31 Aug 2026

Septic is county-run, not state-run
The Williamson County Department of Sewage Disposal Management at 1320 West Main Street, Suite 411 in Franklin, on (615) 790-5751, permits septic systems under regulations of the Williamson County Board of Health. A conventional system permit is $350, or $425 with oversized bathing fixtures; an alternative system is $550, or $575 with oversized bathing fixtures. Soil mapping runs $175 per acre and a preliminary soil investigation $60 per hour.

Williamson County Sewage Disposal, williamsoncounty-tn.gov/126/Sewage-Disposal, and the county Schedule of Application Fees, fetched 31 Aug 2026

Also worth knowing before you build in Williamson County

Where roof pitch rules do apply
Minimum roof pitch appears in four places in the ordinance, all inside special-area-plan districts and several tied to a named road. Grassland Village Character 2 requires 7:12 along Old Hillsboro Road and 5:12 along Hillsboro Road, with gabled or hipped roofs and a one-foot minimum eave overhang. Character 3 requires 7:12. Character 4 and the Triune Character Areas require 5:12 facing state highways and 7:12 facing everything else. None of these reach RP-5 or RD-5 land.

Williamson County Zoning Ordinance Article 10 Section 10.02, Grassland Village and Triune character districts, revision dated 10 June 2025, fetched 31 Aug 2026

No minimum house size
The Williamson County Zoning Ordinance sets no minimum heated floor area for a dwelling in any district. Its only reference to habitable floor area is in the definitions, which defer to the building code and exclude cellars. For a county with a median owner-occupied home value of $751,900, that is a more permissive position than most buyers expect.

Williamson County Zoning Ordinance Article 22 definitions, revision dated 10 June 2025, and US Census Bureau QuickFacts 2020-2024, fetched 31 Aug 2026

Attach the shop and the setback changes
Section 11.04(3) of the zoning ordinance treats an accessory structure within 10 feet of the house as part of the principal structure, and does the same for one within 20 feet that is connected by a roofline. Run a shop bay under one continuous roof with the living space and the whole building has to clear the 100 ft front setback, not an accessory setback. That is worth knowing before the site plan is drawn.

Williamson County Zoning Ordinance Section 11.04(3) Exceptions and Exclusions, revision dated 10 June 2025, fetched 31 Aug 2026

What the county charges
The building permit fee is $1,660 for the first $500,000 of valuation plus $2.00 per additional thousand, with a plan-checking fee of half the permit fee on top. Fees are doubled if work starts before the permit issues. Add a $2.00 per square foot residential privilege tax, a $150 storm water fee on a residential lot, and $50 per re-inspection. The Zoning Certificate that has to come first is free.

Williamson County Schedule of Permit Fees and Schedule of Application Fees, williamsoncounty-tn.gov, fetched 31 Aug 2026

Education Impact Fee by house size
Outside the Franklin Special School District, which is where unincorporated county land sits, the fee runs $3,374 for 1,399 sq ft or less, $6,018 to 1,899 sq ft, $8,033 to 2,399 sq ft, $9,679 to 2,899 sq ft, $11,046 to 3,399 sq ft and $12,237 at 3,400 sq ft or more. Inside the Franklin Special School District the same bands run $1,103 to $4,506. The schedule was revised on a TischlerBise study and took effect 1 March 2020.

Williamson County Community Development fact sheet, Williamson County Revises Education Impact Fee, effective 1 March 2020, fetched 31 Aug 2026

Inspections on a house here
Ten inspections: footings, foundation, slab, slab plumbing where it applies, framing, mechanical, plumbing, insulation, storm water, and the final building inspection that releases the certificate of occupancy. Plans are submitted and inspections booked through the county's electronic plan review system. The county states that plans need not be drawn by a registered design professional unless the complexity of the project warrants it.

Williamson County Inspections, williamsoncounty-tn.gov/396/Inspections, and Adopted Codes, fetched 31 Aug 2026

Climate zone and envelope
Williamson County is IECC climate zone 4A. Only fourteen West Tennessee counties sit in zone 3A; everything else in the state, this county included, is 4A. The county enforces the 2018 energy code with the 2009 tables, so the insulation, fenestration and duct-testing requirements are looser than a current national source will describe.

Tennessee Residential Energy Code 2018 Table R301.1 county list via up.codes, and Williamson County Adopted Codes, fetched 31 Aug 2026

Growth and building activity
272,061 residents as of the July 2025 estimate, up 9.8% since the 2020 census and up from 183,182 in 2010, across 582.86 square miles. The county recorded 1,621 building permits in 2025 against 103,674 housing units. Median household income is $135,594 and the median value of an owner-occupied home is $751,900.

US Census Bureau QuickFacts, Williamson County Tennessee, FIPS 47187, fetched 31 Aug 2026

Seven authorities share one county
The Williamson County growth plan, drawn under Tennessee Code Annotated Title 6, Chapter 58, Part 1, maps urban growth boundaries, planned growth areas and rural areas across seven jurisdictions: Brentwood, Fairview, Franklin, Nolensville, Spring Hill, Thompson's Station and the unincorporated county. The final plan was recorded on 3 January 2025. The zoning ordinance even sets a default for de-annexed land, designating it RP-5 if it lies west of I-65 and RD-5 if east.

Williamson County Growth Plan Update, williamsoncounty-tn.gov/2082/Growth-Plan-Update, and Zoning Ordinance Section 10.01, fetched 31 Aug 2026

Accessory dwelling limits
One accessory dwelling unit per parcel, whatever the number of principal dwellings. It is capped at 750 sq ft or 25% of the principal dwelling, whichever is greater, and can never exceed 75% of it. A deed restriction has to be recorded with the Register of Deeds before the zoning certificate and building permit issue, and an interior apartment must keep the exterior reading as a single-family home, with no second front door.

Williamson County Zoning Ordinance Section 11.04(D)(1) Accessory Dwelling Units, revision dated 10 June 2025, fetched 31 Aug 2026

An excavator grading a compacted building pad on a cleared lot, with survey stakes and a drainage swale visible.
Below the slab

The expensive surprises are in the ground, not the building

What moves a Tennessee budget is usually below grade: limestone sitting shallow, karst voids and sinkholes, and slope. Those are the same conditions that decide whether a septic field passes its soil and site evaluation, so the grading plan, the footing depth and the drainfield get resolved together rather than one at a time. We price the dirt before we price the building.

What we build in Williamson County

All nine services are available across Williamson County. What a build costs depends far more on the parcel than on square footage, so we price against your land rather than publishing a rate card.

Barndominium Kits

Engineered barndominium shell packages delivered to your Tennessee lot, stamped for the criteria your county adopted.

Turnkey Builds

Start to finish barndominium construction: we handle permits, slab, shell, and full interior finish.

Custom Plans

Barndominium floor plans drawn to your land, your family, and the residential code your county actually enforces.

Post-Frame Homes

Pole barn construction adapted into full residences, with wide clear spans and fast dry-in.

Steel Construction

Red-iron and light-gauge steel framing: no rot, no termites, engineered to your county’s adopted wind criteria.

Shouses

Shop and house in one building: workspace and living space under a single roof and a single permit.

Metal Homes

Full metal-clad residences: low maintenance envelopes specified to your Tennessee climate zone.

Site Preparation

Clearing, grading, pad, drainage, and utilities: the work that decides whether the build goes smoothly.

Permitting & Engineering

Sealed structural engineering and the permit that depends on it, from submittal through final inspection.

What a build looks like

Three stages every Williamson County project passes through, from a raw parcel to a finished home. Site work first, because that is where the budget is decided.

Aerial view of an undeveloped rural lot with cleared grass, a cedar and hardwood treeline, and a pale gravel access track.
Stage one

The parcel

Zoning, setbacks, flood zone and utility access get checked before anything is drawn.

An excavator grading a compacted building pad on a cleared lot, with survey stakes and a drainage swale visible.
Stage two

Pad and permit

Clearing, grading and a compacted pad, while the submittal works through Williamson County.

A finished barndominium at dusk with warm interior lighting glowing through its large windows.
Stage three

Frame to finish

Shell erected and dried in, then systems, insulation and interior finish through to CO.

Those are the rules for Williamson County. Tell us what you want to build and we will draw it to them.

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Where we build around Williamson County

Williamson County and the rural land around it. The buildable acreage for a project this size usually sits outside the city limits, which is frequently what changes who issues your permit.

Our Williamson County service area, covering Williamson County and the surrounding rural acreage. We build across this area from our office in Franklin, TN — this map marks the territory we serve, not a branch location.

Keep reading

The questions that usually come next once you know what Williamson County allows.

Barndominium Cost Guide

Sourced per-square-foot ranges by tier and by size, with a calculator built on the same figures.

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Is It Legal in Tennessee?

Classification, zoning, the HOA gate, and why "nonresidential farm building" does not cover a home.

Read it

How Long Does It Take?

Census build-duration data, and what actually sets the permit clock where you are building.

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Sources for this page

The primary documents behind the Williamson County figures above. We would rather you checked them than took our word for it.

Nearby areas we build in

Others we cover in this part of Tennessee. The permitting authority, the adopted design criteria and the zoning can all differ from one to the next.

Nashville

Davidson County
Maury County

Maury County
Rutherford County

Rutherford County

Building in Williamson County: common questions

8 questions we get asked most often about building in Williamson County. If yours is not on the list, ask it directly.

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Can I clad a house in metal in Williamson County?
Yes. This is the county where people most expect the answer to be no, and the ordinance says otherwise. A full-text reading of the 436-page zoning ordinance turns up one prohibition on metal siding, in Section 11.03, and it is a use-specific standard for craft distilleries, sitting alongside a 25-acre site minimum, a 12,500 sq ft floor area cap and a 5,000-barrel storage cap. It does not scope to a dwelling. The mobile-home chapter, which is where cladding bans often hide, regulates steps, decks, handrails and skirting and says nothing about a site-built house. There is no minimum roof pitch, no minimum floor area, no required masonry percentage and no maximum height for a dwelling in the county's rural districts. Where appearance is regulated, it is regulated in the Grassland Village and Triune character districts, which are small mapped areas, and in some cases the rule turns on which road the building faces.
Does the county permit my land, or does a city?
The Williamson County Building Codes Division on West Main Street in Franklin permits and inspects the unincorporated county only. Franklin, Brentwood, Spring Hill, Nolensville, Fairview and Thompson's Station each run their own building department and apply their own zoning, and all six are separately certified to the state. That matters more here than in most Tennessee counties, because the growth plan gives every one of those municipalities an urban growth boundary and annexation lines follow paperwork rather than anything visible from the road. Check the parcel before you commit to a lot. Two things follow the land into the cities regardless: the $2.00 per square foot residential privilege tax applies county-wide including inside the cities, and septic permitting stays with the county Department of Sewage Disposal Management.
Which zoning district do I want, and how much land do I need?
RP-5 if the land is west of I-65, RD-5 if it is east. The ordinance draws the line at the interstate in the district purpose statements themselves. Both districts allow a single-family dwelling on a parcel of record by right, both set a 5-acre minimum lot in a traditional subdivision with a density cap of one unit per five acres, both require 200 ft of lot width, and both set setbacks of 100 ft front, 25 ft side and 50 ft rear. Neither imposes a maximum height. A conservation subdivision is the alternative, with an average lot of three-quarters of an acre and a half-acre minimum, tighter setbacks, and a requirement that smaller lots sit internally or out of sight of neighbouring property. The Voluntary Agricultural District exists as well, but it needs a 15-acre minimum and a rezoning application from the owner.
Which building code applies here, and is it the same as the rest of Tennessee?
No, and this catches people out. The statewide residential code is the 2018 International Residential Code. Williamson County adopted the 2021 IRC locally with an effective date of 30 September 2024, which Tennessee law allows a local government to do. So a plan set worked up against the statewide edition is an edition behind what this county enforces. The county keeps two statewide amendments in place: automatic fire sprinklers in one- and two-family dwellings are excluded, and the electrical chapters are deleted, with electrical permits going through the state at core.tn.gov since June 2023. The energy code stays at the 2018 edition using the 2009 tables, so the envelope and duct requirements are considerably looser than a current national article will tell you.
What design wind speed and seismic category should the engineer use?
Williamson County has not published a filled-in Table R301.2(1). Tennessee leaves ultimate design wind speed, ground snow load, frost line depth, seismic design category, weathering and termite exposure for each jurisdiction to fill in, and this county has left the table blank. That is worth knowing rather than working around, because a clear-span steel or post-frame building exceeds the prescriptive tables and becomes an engineered structure under IRC R301.1.3, so the figures actually drive the base connections and anchor bolts. There is an extra wrinkle here: the state amendment substitutes an older seismic figure into the 2018 code, and Williamson adopted the 2021 edition on its own authority. We settle the criteria directly with the Building Codes Division on (615) 790-5718 for your parcel before a Tennessee-licensed engineer stamps anything.
Who handles the septic permit?
The Williamson County Department of Sewage Disposal Management, in Suite 411 of the same West Main Street building as Building Codes, on (615) 790-5751. It works to regulations adopted by the Williamson County Board of Health rather than sending you to the state, and it publishes its own fee schedule: $350 for a conventional system permit, $550 for an alternative system, and $425 or $575 respectively where the house has oversized bathing fixtures. A large soaking tub or a multi-head shower can move the permit into the higher band, so it is worth raising early. Soil mapping is billed at $175 per acre and preliminary soil investigation at $60 an hour. Drip-emitter and cluster systems carry a second layer: Article 20 of the zoning ordinance adds county requirements on top of the state rules, administered by the Williamson County Water and Wastewater Authority, and no building permit or certificate of occupancy issues for a parcel that does not conform.
What will the county charge before I break ground?
A Zoning Certificate has to be approved first and costs nothing. The building permit fee is $1,660 for the first $500,000 of valuation plus $2.00 for each additional thousand, with a plan-checking fee equal to half the permit fee payable when plans go in. Then there is a residential privilege tax of $2.00 per square foot and, outside the Franklin Special School District, an Education Impact Fee that runs from $3,374 for a house of 1,399 sq ft or less up to $12,237 at 3,400 sq ft or more. Storm water review on a residential lot is $150 and a failed inspection costs $50 to re-book. Two figures to keep in mind: the fee schedule doubles the permit fee where work begins before the permit issues, and the impact fee is banded by heated square footage, so the difference between 2,899 and 2,900 sq ft is a real number.
Is my building exempt because it is agricultural?
Almost certainly not, and this is the most expensive misconception in the category. Tennessee Code Annotated Section 68-120-101(c) exempts nonresidential farm buildings from the statewide standards. The load-bearing word is nonresidential. The moment the building contains a dwelling unit it is a one- or two-family dwelling and the exemption is gone, however agricultural the shell looks and however the land is assessed. Williamson County does not use the word barndominium anywhere in its zoning ordinance, so there is no special category to fall into: the county reads the building as a single-family dwelling and permits and inspects it as one. If part of the structure is genuinely a barn nobody lives in, the Building Codes Division publishes an agricultural exemption form and is the right place to ask how it applies to a mixed building.

What clients say

4.9 out of 5 based on 8 reviews Placeholder content

We had ten acres outside town and no idea what we could legally put on it. They pulled the zoning and the A-1 lot minimum before we spent anything on drawings, which saved us from buying plans for a building that would not have been approved.

Dale W. July 18, 2026

Ordered the shell kit and erected it with my brother-in-law over about six weekends. The drawings were clear, the bolt schedule matched what showed up on the truck, and the county inspector had no issues with the engineering.

Marisol T. June 2, 2026

Turnkey from a cleared lot to certificate of occupancy. What I appreciated most was that when plan review came back with comments, I heard about it the same day along with what they were doing about it.

Ray B. April 27, 2026

Building in Williamson County?

Start with the plan. Tell us what you want to build and we will draw it, then confirm what Williamson County will actually let you put on the parcel and what wind load it has to meet. That conversation costs nothing.

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