01 — Coverage
Jurisdictions Covered
Williamson County contains multiple municipalities, each with its own code adoption and local amendments. Nail'd It's AI compliance layer must identify project jurisdiction before applying parameters.
Williamson County
Unincorporated Areas
Building: 2021 IRC / IBC
Energy: 2018 IECC
Electrical: State of TN (CORE)
Plumbing/Mech: 2021 IPC / IMC
📞 (615) 790-5718 · Electronic Plan Review System
Franklin
City of Franklin
Building: 2024 IRC / IBC
Zoning: Franklin Zoning Ordinance 2024
Districts: R1, R2, R3, OR, AG, Historic
Note: Historic Districts require ARB review
📍 Building & Neighborhood Services · franklintn.gov
Brentwood
City of Brentwood
Building: 2018 IRC
Energy: 2018 IECC
Note: ARB aesthetic review required
Update: 2025 code update pending (Apr 17)
📞 Chief Building Official: Michael Rinehart (615) 577-6163
Spring Hill
City of Spring Hill (partial Williamson Co.)
Building: 2018 IRC
Zoning: Unified Development Code (UDC)
NFIP: Flood compliance required
Electrical: Jeff Hearne (615) 435-9715
📞 Chief Building Official: Victor Woods (931) 451-0162
Nolensville
Town of Nolensville
Building: Williamson County overlay
Note: Verify jurisdiction-specific amendments
Process: Apply via Williamson County offices
📍 1320 West Main St., Franklin, TN 37064
Fairview
City of Fairview
Building: Planning & Codes Dept.
Note: Separate permit process from county
Verify: Local amendments before build
📍 fairview-tn.org/depts-services/planning-codes-dept
AI Platform Rule — Jurisdiction First
Before any compliance parameters are applied to a project, the system must confirm the exact parcel jurisdiction. County codes and municipal codes differ. Applying the wrong ruleset is a hard failure.
02 — Code Framework
Adopted Building Codes
| Code | Edition | Jurisdiction | Notes |
|---|---|---|---|
| International Residential Code (IRC) | 2021 | Williamson County (unincorporated) | Fire sprinkler requirement excluded per TN state law |
| International Residential Code (IRC) | 2024 | City of Franklin | Most current adoption in the county |
| International Residential Code (IRC) | 2018 | Brentwood / Spring Hill | 2025 update pending for Brentwood (Apr 17, 2025) |
| International Building Code (IBC) | 2021 | Williamson County / Franklin | Applies to non-residential and mixed-use structures |
| International Energy Conservation Code (IECC) | 2018 | County-wide | References 2009 tables for TN state alignment |
| International Plumbing Code (IPC) | 2021 | Williamson County | Municipal jurisdictions may vary |
| International Mechanical Code (IMC) | 2021 | Williamson County | Covers HVAC installation standards |
| National Electrical Code (NEC) | State-administered | All jurisdictions | Electrical permits via TN State at core.tn.gov — separate from county |
| Tennessee Fire Marshal Codes | Updated Apr 17, 2025 | State overlay — all jurisdictions | Grace period applies for plans in review at adoption date |
03 — Permit Requirements
Permit Requirements for Custom Homes
📋 Required Permit Documents
- ✓Completed permit application form
- ✓Architectural drawings — floor plans + elevations
- ✓Site plan showing property lines, existing structures, easements
- ✓Contractor license and insurance proof
- ✓Geotechnical report (required if slope ≥ 20% — Franklin)
- ✓Lot coverage calculation (house + impervious surfaces)
- ✓Stormwater management plan
- ✓Electrical permit — separate via TN State (core.tn.gov)
📐 When a Permit is Required
- ✓All new custom home construction — always required
- ✓Any accessory structure ≥ 120 sq ft
- ✓Any structure on a permanent foundation (any size)
- ✓Additions, garages, decks, pools, fencing
- ✓Grading/excavation beyond minor landscaping
- ✓Driveway or parking pad changes (Franklin)
- ✓Septic system installation or modification
- ✓HVAC system installation
Self-Build Owner Rule
Homeowners may pull their own permits for owner-occupied builds (not for resale or lease). Limited to one permit every 24 months. Cannot exceed contractor licensing thresholds.
Electronic Plan Review
Williamson County uses an Electronic Plan Review System for online permit submission. Franklin and Brentwood use their own online portals. All require account registration before submission.
04 — Zoning & Setbacks
Zoning Districts & Setback Parameters
Setback distances and height limits are jurisdiction and district-specific. The parameters below represent standard residential district baselines. Always verify against the specific parcel's zoning designation before planning.
| Parameter | Typical Range | Jurisdiction | Notes |
|---|---|---|---|
| Front Yard Setback | 25 – 50 ft | All | Varies by district (R1/R2/R3); Franklin 2024 Ordinance governs city parcels |
| Side Yard Setback | 5 – 15 ft | All | Corner lots may have dual front setback requirements |
| Rear Yard Setback | 20 – 30 ft | All | Varies by district; accessory structures subject to same rules |
| Maximum Building Height | 35 ft (typical) | Franklin / County | IRC establishes baseline; local zoning ordinance controls |
| Lot Coverage (Impervious) | Varies by district | All | Includes house footprint + driveway + hardscape; stormwater review triggered |
| Accessory Structure Height | Must not exceed main home | County | Cannot be larger or taller than primary residence |
| Historic District Setbacks | ARB-determined | Franklin Historic Districts | HARD GATE ARB approval required before permit issuance |
| Agricultural (AG) Zone | Larger lots; farming overlay | Franklin | Limited residential density; farmland preservation rules apply |
| Flood Plain Compliance | NFIP standards | Spring Hill / All | HARD GATE Flood zone parcels require NFIP compliance before permit |
| Steep Slope (≥ 20%) | Geotech report required | Franklin | Triggers extra Planning/Engineering review before permit issuance |
AI Platform Rule — Parcel-Level Verification Required
Setback and height parameters must be verified at the parcel level using the specific zoning designation. Do not apply district-wide averages as hard compliance values. Flag any parcel in a Historic District, flood plain, or steep slope zone for human review before scheduling begins.
05 — Energy Efficiency
2018 IECC Compliance Parameters
All custom homes in Williamson County must comply with the 2018 International Energy Conservation Code. These are minimum performance standards — the AI system should use these as hard floor values for material sourcing specifications.
Ceiling Insulation
R-49
Minimum R-value for attic / ceiling assembly
Wall Insulation
R-20
Exterior walls; continuous insulation options available
Floor Insulation
R-19
Over unconditioned spaces (crawlspace, garage)
Window U-Factor
≤ 0.30
Maximum U-factor for fenestration assemblies
Window SHGC
≤ 0.25
Solar Heat Gain Coefficient — south/west exposures critical
Air Sealing
≤ 3 ACH50
Blower door test required — 3 air changes per hour at 50 pascals
HVAC Duct Leakage
≤ 4 CFM25
Duct leakage to outside at 25 pascals per 100 sq ft
Water Heater
EF Required
Energy Factor compliance per equipment type and size
AI Material Sourcing Integration Point
These IECC values are hard floor specs for material sourcing. When the AI system sources insulation, windows, or HVAC equipment, all sourced products must meet or exceed these minimums. Any product spec below these values is an automatic disqualification.
06 — Inspection Sequence
Required Inspections — Custom Home
Tennessee state minimum is three inspections for site-built homes. Williamson County requires staged inspections aligned with the IRC. Each inspection is a gate — the next phase cannot begin until the previous inspection passes.
1
Foundation Inspection HARD GATE
- ▸Footings and slab preparation verified
- ▸Flood plain and grading compliance confirmed
- ▸Structural support layout reviewed
- ▸Separate footing inspection required if slab under living space
- ▸Must pass before concrete is poured
2
Framing / Rough-In Inspection
- ▸Structural framing, shear walls, roof assembly
- ▸Windows and doors installed
- ▸Rough-in plumbing reviewed
- ▸Rough-in mechanical (HVAC) reviewed
- ▸Rough-in electrical reviewed (state inspector)
3
Insulation / Energy Inspection HARD GATE
- ▸Insulation R-values verified against 2018 IECC
- ▸Air sealing reviewed before drywall
- ▸Blower door test scheduled
- ▸Must pass before drywall installation begins
4
Plumbing & Mechanical Inspection
- ▸Rough-in pipe runs, pressure tested
- ▸HVAC duct runs and venting verified
- ▸Gas line rough-in reviewed (if applicable)
- ▸Systems testing at final stage
5
Electrical Inspection (State)
- ▸Administered by TN State — separate permit via core.tn.gov
- ▸Rough-in wiring, panel, fixtures
- ▸State inspector schedules independently of county
6
Interior Finishes Inspection
- ▸Cabinetry, countertops, flooring, trim
- ▸Appliances and lighting fixtures
- ▸Punch list items verified
7
Final Inspection → Certificate of Occupancy HARD GATE
- ▸All systems operational — HVAC balancing, plumbing, electrical
- ▸Blower door and duct leakage final test results submitted
- ▸Site work and grading complete
- ▸All prior inspections passed and documented
- ▸Certificate of Occupancy issued only upon full pass
07 — Structural & Systems
Structural & Systems Parameters
| System | Standard | Key Requirements | Flag |
|---|---|---|---|
| Foundation | 2021 IRC Chapter 4 | Footings below frost depth; slab on grade requirements; drainage away from structure | Hard Gate |
| Framing | 2021 IRC Chapter 5–8 | Stud size, spacing, header sizing per span tables; shear wall requirements in load paths | Required |
| Roofing | 2021 IRC Chapter 9 | Ice/water shield at eaves; ventilation ratios; deck attachment per wind zone | Required |
| Plumbing | 2021 IPC | DWV sizing, water supply pressure, fixture unit counts, water heater TPR valve | Required |
| HVAC / Mechanical | 2021 IMC | Load calculation (Manual J) required; duct sizing per Manual D; combustion air provisions | Required |
| Electrical | NEC (State) | Panel sizing, circuit protection, AFCI/GFCI requirements per NEC; separate state permit | State Permit |
| Septic / Sewer | TN Dept. of Environment | Percolation test required for septic; county approval for sewer connection | Varies |
| Stormwater | County + Municipal | Impervious surface limits; drainage plan required; erosion control during construction | Required |
| Fire Sprinklers | IRC — Excluded | Not required in Williamson County per TN state law opt-out | State Opt-Out |
08 — AI Platform Integration
AI Compliance Flags for Nail'd It Platform
These are the decision rules the AI system must enforce when processing a new project in Williamson County.
🚨 Hard Gates — Require Human Approval
- 🔴Parcel in a FEMA flood zone — NFIP compliance required before scheduling
- 🔴Franklin Historic District — ARB review required before permit
- 🔴Slope ≥ 20% — Geotechnical report required before permit (Franklin)
- 🔴Foundation inspection not passed — concrete pour blocked
- 🔴Insulation inspection not passed — drywall blocked
- 🔴Final inspection not passed — Certificate of Occupancy blocked
⚡ Auto-Triggers — AI Executes Without Human Approval
- 🟡Jurisdiction confirmed → apply correct code edition automatically
- 🟡Material spec below IECC minimums → flag and source compliant alternative
- 🟡Inspection passed → release next phase material orders
- 🟡Inspection failed → pause subcontractor scheduling, alert PM
- 🟡Electrical permit → route to TN State (core.tn.gov) automatically
- 🟡Accessory structure ≥ 120 sq ft → flag permit requirement
📋 Pre-Project Checklist (AI Runs at Project Creation)
- ☐Confirm parcel jurisdiction (county vs. municipality)
- ☐Pull zoning designation and setback parameters
- ☐Check flood zone status (FEMA FIRM map)
- ☐Check slope for geotechnical requirement trigger
- ☐Confirm Historic District status
- ☐Identify applicable code edition
- ☐Confirm septic vs. sewer connection
- ☐Flag electrical permit routing (TN State)
📦 Material Sourcing Compliance Rules
- ☐Insulation: source only products meeting R-value minimums
- ☐Windows: source only U-factor ≤ 0.30, SHGC ≤ 0.25
- ☐HVAC: Manual J load calc must complete before equipment sizing
- ☐Duct materials: spec to achieve ≤ 4 CFM25 leakage
- ☐Foundation materials: spec per frost depth requirements
- ☐Never source fire sprinkler systems for Williamson Co. residential