Residential Building Permit (New Construction) in Thornton, Colorado
Required for new single-family homes and other new residential construction in Thornton. Reviewed against the 2024 International Residential Code (IRC) with Thornton amendments (including the City's own Table R301.2 climatic/geographic design criteria), effective July 1, 2025, and issued by the City Development Building Inspection Division.
Verified 2026-06-30 · Source
When you need this permit
- Building permit required for new single-family dwellings, room additions, and attached/detached garages
- Applications submitted online via the CityView Portal (cityviewportal.thorntonco.gov)
- Plans must comply with the 2024 IRC with Thornton amendments and the 2024 IECC (including Colorado Model Electric Ready and Solar Ready Code provisions)
- Structural design must meet Thornton's amended Table R301.2 criteria: 30 psf ground snow load, 105 mph ultimate wind speed, Seismic Design Category B, 36-inch frost depth, Severe weathering exposure
- Homeowners may qualify for expedited one-business-day review for complete, standard-code submittals
- Valuation is the estimated cost to replace the building in kind (labor, materials, overhead, profit); new construction valuation may be calculated using ICC square-footage valuation tables
Required documents
- Req
Building Permit Application (CityView Portal)
Online application through the City of Thornton's CityView Portal
- Req
Site Plan
Property lines, setbacks, existing/proposed structures, easements, drainage
- Req
Construction Drawings
Full plan set: foundation, framing, structural, mechanical, plumbing, electrical, bearing the seal/signature of a design professional where required
- Opt
Plumbing Data Worksheet
2024 IPC water fixture unit (F.U.) calculation sheet, required when adding fixtures to an existing water service; also used for ADU and tenant-finish plumbing scope
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Building Permit Fee — valuation $1.00 to $500 | $30.00 | City of Thornton 2026 Building Permit Fee Schedule, effective January 1, 2026 (updated 11/25/2025) |
| Building Permit Fee — valuation $501 to $2,000 | $30.00 for the first $500 plus $3.15 for each additional $100 or fraction thereof | — |
| Building Permit Fee — valuation $2,001 to $25,000 | $75.75 for the first $2,000 plus $14.40 for each additional $1,000 or fraction thereof | — |
| Building Permit Fee — valuation $25,001 to $50,000 | $397.75 for the first $25,000 plus $10.40 for each additional $1,000 or fraction thereof | — |
| Building Permit Fee — valuation $50,001 to $100,000 | $650.25 for the first $50,000 plus $7.20 for each additional $1,000 or fraction thereof | — |
| Building Permit Fee — valuation $100,001 to $500,000 | $1,000.25 for the first $100,000 plus $5.75 for each additional $1,000 or fraction thereof | — |
| Building Permit Fee — valuation $500,001 to $1,000,000 | $3,240.25 for the first $500,000 plus $4.90 for each additional $1,000 or fraction thereof | — |
| Building Permit Fee — valuation $1,000,001 and up | $5,615.25 for the first $1,000,000 plus $3.75 for each additional $1,000 or fraction thereof | — |
| Plan Review Fee | 65% of the Building Permit Fee | Third Party Plan Review Fee = 65% of Building Permit Fee, or Third-Party Review Fee + 10%, whichever is greater |
| Mechanical, Electrical & Plumbing Permit Fee — New Single Family Dwelling | $100.00 | Flat combined MEP fee for new single-family residential buildings, per the 2026 Fee Schedule |
| Use Tax | 3.75% of 50% of valuation, or 100% of total material cost | — |
Review timeline
1–13 business days
Thornton’s published plan-review target
Inspection process
- 1
Foundation / Footings
Before concrete pour; footings must extend below the 36-inch amended frost line and not less than 12 inches below undisturbed ground
- 2
Framing
After framing complete, before insulation or wall cover
- 3
MEP Rough-In
Mechanical, electrical, and plumbing rough-in before walls closed
- 4
Insulation / Energy
Insulation and 2024 IECC compliance verification before drywall
- 5
Final
All work complete, ready for Certificate of Occupancy
Tips
- Thornton adopted the 2024 I-Codes and 2023 NEC effective July 1, 2025, replacing the 2021 I-Codes/2017 NEC — confirm your submittal date against this cutover.
- Thornton repealed and reenacted its own IRC Table R301.2 rather than using a generic value: 30 psf ground snow, 105 mph ultimate wind speed, Seismic Design Category B, 36-inch frost depth — cite these Thornton-specific values in structural calculations.
- Homeowners can request expedited review (target: complete within one business day) for straightforward, complete, standard-code residential projects via the CityView Portal.
- New construction valuation can be calculated via ICC square-footage tables rather than a submitted contract price.
Frequently asked questions
- Which building code edition does Thornton use?
- Thornton adopted the 2024 International Building Code, International Residential Code, and related I-Codes, plus the 2023 National Electrical Code, effective July 1, 2025 (ordinance adopted May 13, 2025). These replaced the prior 2021 I-Code / 2017 NEC cycle.
- What are Thornton's structural design values for new residential construction?
- Per Thornton's amended IRC Table R301.2: 30 psf ground snow load, 105 mph ultimate design wind speed, Seismic Design Category B, Severe weathering exposure, 36-inch minimum frost line depth, and slight-to-moderate termite risk. Ice barrier underlayment is not required by the amended table.
Sources & verification
Verified against official sources. Last reviewed 2026-06-30.
- City of Thornton — City Development, Building Inspection Division — official building department
- City of Thornton — Building Permits & Inspections
- City of Thornton 2026 Building Permit Fee Schedule (PDF, effective Jan 1, 2026)
- Ordinance Adopting 2024 I-Codes and 2023 NEC with Thornton Amendments (PDF, incl. Table R301.2)
- City of Thornton — Projects That Require and Don't Require a Building Permit (PDF, updated 10/31/2025)
Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Thornton building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.
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