Quick answer: In Thornton, a contractor must hold a City of Thornton license before the city will issue a building permit, and the contractor normally pulls the permit. Thornton requires permits for siding, most roofing, window and door replacement, basement finishes, attached decks and kitchen work that touches plumbing, gas, electrical or structure. Homes in unincorporated Adams County are permitted by the county, not a city.
Thornton Contractor Licenses
The City of Thornton licenses contractors who build, remodel or repair buildings in the city. Its license classes are Class A General, Class B Building, Class C Residential, Class D Mechanical and Class D Roofing. The city accepts a valid license from a reciprocating jurisdiction or an ICC contractor certification as proof of qualification, but the contractor still has to be issued a Thornton license. Homeowners working on their own primary residence don’t need one.
Who Pulls the Permit Matters
Thornton says the contractor is normally responsible for getting the permit. If a homeowner pulls it instead, the homeowner becomes responsible for the whole project, including workers’ compensation and builder’s liability. That’s a reason to be wary of a contractor who asks you to pull the permit yourself.
What Needs a Permit in Thornton
| Project | Permit? |
|---|---|
| Siding or stucco | Yes |
| Roofing | Yes, except repairs of one square or less |
| Window or door replacement | Yes (glass-only replacement in the existing frame is exempt) |
| Basement finish | Yes |
| Kitchen with plumbing, gas, electrical or structural changes | Yes |
| Cabinets, countertops, paint, flooring | No |
| Attached or above-ground decks | Yes |
| Detached deck under 200 sq ft and under 30 in. high, not at the main exit | No |
Thornton’s list isn’t complete, so confirm your project with the Building Division at 303-538-7250 or Buildings@ThorntonCO.gov.
Unincorporated Adams County
Adams County includes cities like Thornton, Northglenn, Brighton and Commerce City, plus unincorporated areas between them. Each city runs its own permits and licensing, and homes outside city limits go through Adams County. Check which one covers your address before you compare bids, because the license a contractor needs depends on it.
What We Build in Thornton and Adams County
- Roof replacement with Class 4 shingles, Owens Corning Duration STORM or better, at $1,000 per square.
- Siding in James Hardie at $1,600 per square primed and $2,200 in ColorPlus, or LP SmartSide at $1,500.
- Window replacement, which is permitted work in Thornton.
- Basement finishing, kitchens and baths, and decks.
See all our services as a building contractor in Adams County, based in Thornton and the surrounding cities.
Hiring a Contractor in Thornton: FAQs
Do contractors need a license in Thornton, CO?
Yes. Thornton requires contractors to hold a City of Thornton license before a building permit is issued. Homeowners working on their own primary residence are exempt.
Do I need a permit to replace siding in Thornton?
Yes. Thornton lists siding and stucco as work that requires a building permit.
Do I need a permit to replace windows in Thornton?
Yes, replacing windows or doors requires a permit. Replacing only the glass in an existing sash or frame does not.
Who issues permits outside Thornton city limits?
Homes in unincorporated Adams County are permitted by Adams County. Each city in the county runs its own building department.
Should I pull the permit myself to save money?
Thornton warns that a homeowner who pulls the permit becomes responsible for the whole project, including workers’ compensation and builder’s liability. Let your contractor pull it.
Free Estimates in Thornton and Adams County
We give written, fixed-price bids, pull the permits and see every job through final inspection. Josh Brooks Construction and Renovation Inc. is a licensed general contractor based in Longmont with 30 years in construction, serving 46+ Front Range cities. Call 720-828-7997 or text 720-453-5095 for a free estimate.
Licensed. Local. Not a storm chaser.
