Residential Addition / Remodel Permit in Thornton, Colorado
Required for room additions, basement finishes, structural alterations, and remodels to existing homes in Thornton. Reviewed against the 2024 IRC with Thornton amendments; uses the same valuation-based fee table as new construction.
Verified 2026-06-30 · Source
When you need this permit
- Room additions, basement finishes, structural modifications, and attached/detached garages require a building permit
- Remodel/renovation/alteration project valuation is calculated as labor + material cost, or material cost x2, whichever method the applicant provides support for
- Plans must show scope, dimensions, structural connection to the existing structure, and compliance with the amended Table R301.2 design criteria where structural work is involved
- For Accessory Dwelling Units (ADUs) created via basement/garage/attic finish (Integrated ADU), contact Planning before building permit submittal (303-538-7295) — additional zoning requirements apply
- Applications submitted via the CityView Portal
Required documents
- Req
Building Permit Application (CityView Portal)
Online application; select the remodel/addition project scope
- Req
Site Plan
Property lines, existing structures, proposed addition footprint and setbacks
- Req
Construction Drawings
Plans showing the addition/remodel scope, including structural calculations if structural work is involved
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Building Permit Fee — valuation-based (same table as new construction) | Varies by valuation — $30.00 minimum up to $5,615.25 + $3.75/$1,000 over $1,000,000 | City of Thornton 2026 Building Permit Fee Schedule; remodel/renovation/alteration valuation = labor + material cost, or material cost x2 |
| Plan Review Fee | 65% of the Building Permit Fee | — |
| Additional Plan Review (changes, additions, or revisions to plans) | $75.00 or actual hourly cost to the jurisdiction, whichever is greater | — |
| Mechanical, Electrical & Plumbing trade permit fees | $30.00 for the first $1,000 of trade valuation, plus $10.00 for each additional $1,000 or fraction thereof, per trade | Applies when a remodel/addition includes plumbing, mechanical, and/or electrical work — each trade charged separately based on that trade's valuation |
Review timeline
~1–13 business days
Typical estimate — confirm current times with the Thornton building department
Inspection process
- 1
Foundation (if new footings)
Before concrete pour, below the 36-inch amended frost line
- 2
Framing
After framing complete, before insulation or wall cover
- 3
MEP Rough-In
Electrical, plumbing, mechanical rough-in before walls closed
- 4
Final
All work complete per approved plans
Tips
- Thornton calculates remodel/renovation/alteration valuation as labor + material cost, or material cost x2 — different from the ICC-table method used for new construction.
- Basement, garage, or attic finishes that create an Integrated ADU trigger additional zoning review — contact the Planner of the Day (303-538-7295) before applying for the building permit.
- Additional plan review triggered by applicant-requested changes is billed at $75.00 (or actual hourly cost if greater).
Frequently asked questions
- How is the valuation calculated for a remodel in Thornton?
- For remodel, renovation, or alteration projects, Thornton calculates valuation by adding labor and material cost, or by doubling the material cost — as opposed to new construction, which may use ICC square-footage valuation tables.
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 2026 Building Permit Fee Schedule (PDF)
- City of Thornton — Projects That Require and Don't Require a Building Permit (PDF)
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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