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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

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Fee schedule

Building Permit Fee — valuation $1.00 to $500City of Thornton 2026 Building Permit Fee Schedule, effective January 1, 2026 (updated 11/25/2025)
$30.00
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 FeeThird Party Plan Review Fee = 65% of Building Permit Fee, or Third-Party Review Fee + 10%, whichever is greater
65% of the Building Permit Fee
Mechanical, Electrical & Plumbing Permit Fee — New Single Family DwellingFlat combined MEP fee for new single-family residential buildings, per the 2026 Fee Schedule
$100.00
Use Tax
3.75% of 50% of valuation, or 100% of total material cost

Review timeline

Plan reviewThornton’s published plan-review target
1–13 business days

How long did your Residential Building Permit (New Construction) permit actually take in Thornton?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 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. 2

    Framing

    After framing complete, before insulation or wall cover

  3. 3

    MEP Rough-In

    Mechanical, electrical, and plumbing rough-in before walls closed

  4. 4

    Insulation / Energy

    Insulation and 2024 IECC compliance verification before drywall

  5. 5

    Final

    All work complete, ready for Certificate of Occupancy

See the full Thornton inspection guide — scheduling & re-inspection fees →

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

Thornton requires a residential building permit (new construction) for: 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. If your project isn't listed, confirm with City of Thornton — City Development, Building Inspection Division at 303-538-7250 before starting work.

In Thornton, the published Building Permit Fee — valuation $1.00 to $500 is: $30.00. Additional published fees: 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; Mechanical, Electrical & Plumbing Permit Fee — New Single Family Dwelling — $100.00; Use Tax — 3.75% of 50% of valuation, or 100% of total material cost. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Thornton's published plan-review target for a residential building permit (new construction) is 1–13 business days.

You'll need: Building Permit Application (CityView Portal); Site Plan; Construction Drawings. Depending on your project, Thornton may also ask for: Plumbing Data Worksheet. See the required-documents checklist on this page for details on each.

Thornton requires 5 inspection(s) for a residential building permit (new construction), in order: Foundation / Footings, Framing, MEP Rough-In, Insulation / Energy, Final. Schedule each through City of Thornton — City Development, Building Inspection Division (303-538-7250).

Apply through City of Thornton — City Development, Building Inspection Division at 9500 Civic Center Drive, Thornton, CO 80229. Phone: 303-538-7250, email: buildings@thorntonco.gov. Office hours: Mon–Fri, 8:00 a.m.–5:00 p.m. (counter payments 8:00 a.m.–4:30 p.m.). Official information: https://www.thorntonco.gov/business-development/city-development/building-permits-inspections.

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.

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.

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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