Williamson County, Tennessee — home to Brentwood, Franklin, Spring Hill, Nolensville, and Fairview — has become one of the most desirable suburban destinations in the Southeast. With that growth comes a very active building department processing thousands of residential permits every year.
Building codes in unincorporated Williamson County are administered by the Williamson County Building and Codes Department, located at 1320 West Main Street, Suite 113, Franklin, TN 37064. Their number is (615) 790-5718.
What Requires a Building Permit in Williamson County
Sheds in Williamson County: Know Before You Buy
Williamson County's 144 sq ft threshold is on the stricter end. A standard 12×12 shed is exactly at the limit. Common shed sizes that require a permit include:
- 12×12 = 144 sq ft — at the threshold, requires a permit
- 10×16 = 160 sq ft — requires a permit
- 12×16 = 192 sq ft — requires a permit
- 16×20 = 320 sq ft — requires a permit
Sizes below the threshold (common examples):
- 10×12 = 120 sq ft — no permit required
- 10×14 = 140 sq ft — no permit required
- 8×16 = 128 sq ft — no permit required
Setback Requirements for Sheds in Williamson County
Even permit-exempt sheds must comply with accessory structure setbacks. In most residential zones in unincorporated Williamson County:
- Rear yard: 5 feet from the rear property line
- Side yard: 5 feet from the side property line
- Front yard: Not permitted within the front yard setback area
- Distance from house: At least 6 feet from any other structure
Agricultural zones have different (more lenient) setback rules. If you're on a larger rural parcel, verify your specific zoning with the county planning department.
Deck and Porch Permits in Williamson County
The Tennessee Residential Building Code requires a building permit for decks and porches attached to the primary structure, regardless of size. The most commonly misunderstood rule: replacing the decking boards on an existing permitted deck does not require a new permit (it's considered maintenance). But adding to the deck, changing the footprint, or replacing structural members does require a permit.
What the Deck Permit Review Includes
Williamson County inspectors review deck plans for:
- Footing size and depth (frost line in Middle Tennessee is 12 inches)
- Post size and height relative to span
- Beam and joist sizing based on span tables in the IRC
- Ledger board attachment method and flashing details
- Railing height (42 inches required for decks more than 30 inches above grade) and baluster spacing
- Stair riser and tread dimensions
- Guard rail at stairs
Pool Permits in Williamson County
All swimming pools in unincorporated Williamson County require a building permit — including above-ground pools over 24 inches in depth. The permit process for pools involves multiple sub-permits: building, electrical, and plumbing (if applicable). Additionally, Tennessee law requires a physical barrier (fence or pool cover) around pools before anyone can use them, and this barrier is inspected as part of the final approval process.
Above-ground pools often surprise homeowners. Even though they're temporary structures that can be taken down, a 4-foot above-ground pool still requires a permit and barrier inspection if it's deeper than 24 inches.
How to Apply for a Building Permit in Williamson County
Williamson County Building and Codes accepts applications in person and by email for most projects. The county's online portal has expanded in recent years. Here's the general process:
- Determine your project type and confirm you're in unincorporated Williamson County (not a city).
- Prepare your application materials. For sheds: a completed application form and a site plan. For decks: application, site plan, and construction drawings. For new structures: all of the above plus a drainage site plan.
- Submit your application in person at 1320 West Main Street, Suite 113, Franklin, TN 37064, or email to the building department (check the county website for the current submission email, as it changes periodically).
- Pay the permit fee. Williamson County calculates fees based on the estimated project value. Typical fees:
- Shed permit: $50–$120
- Deck permit: $75–$200
- Pool permit: $150–$350
- Home addition: $200–$800+ depending on size
- Wait for review. Simple accessory structure permits typically take 3–7 business days. More complex projects take longer. Williamson County does not currently have an online status-check portal for all permit types — you may need to call to check status.
- Post your permit card at the job site before work begins.
- Schedule inspections. Call (615) 790-5718 to schedule. Give at least 24 hours' notice.
Tips for Faster Approval in Williamson County
Given the volume of permits Williamson County processes, these steps help avoid common delays:
- Include your parcel ID on the application. Find it on your property tax bill or the Williamson County Assessor's website.
- Draw your site plan to scale. A sketch that's clearly dimensioned is usually sufficient for simple accessory structures, but scaled drawings reduce back-and-forth.
- Label setbacks on the site plan. Show the measured distance from your proposed structure to each property line. This is the most common missing piece.
- Include HOA approval if applicable. The county doesn't require it, but if you later need to prove HOA approval, having it documented up front avoids issues.
Frequently Asked Questions — Williamson County TN
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Yes. A 10×16 shed is 160 square feet, which exceeds Williamson County's 144 sq ft threshold. A building permit is required. You'll need to submit a site plan and pay a fee, typically $50–$120. An inspection will be required once the shed is placed — call (615) 790-5718 to schedule it. If you're inside Franklin, Brentwood, Spring Hill, or another city, contact that city's building department instead.
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Unincorporated Williamson County does not require a building permit for fences. However, you must comply with setback rules and height restrictions in your zoning district. Standard privacy fences (6 feet in rear and side yards) are generally allowed without a permit. If you're inside Franklin or Brentwood, those cities do require fence permits for certain types — contact your city's codes department.
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The frost depth in Middle Tennessee, including Williamson County, is 12 inches. This means footings for decks, pergolas, detached garages, and other permitted structures must be placed at least 12 inches below grade to avoid frost heave. The inspector will verify footing depth during the foundation inspection — don't backfill until after this inspection passes.
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Yes — Tennessee allows homeowners to act as their own general contractor for construction on their own residence. You'll note this on the permit application. However, electrical, HVAC, and plumbing sub-permits still require licensed subcontractors in Tennessee. If you're doing any electrical work (including running power to a shed), a licensed electrician must perform and permit that work.
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Williamson County building permits are typically valid for 12 months from the date of issuance. Work must begin within 6 months of the permit issuance, and at least one inspection must be passed within 12 months to keep the permit active. If the project takes longer, you can apply for a permit extension before the expiration date. Expired permits require a new application and fee.