Colorado's Wildfire Resiliency Code for Homeowners

Wildfire isn't just a mountain problem anymore. The December 2021 Marshall Fire burned through suburban neighborhoods in Boulder County. The Colorado Resiliency Office calls it the state's most destructive fire, destroying over 1,000 structures and killing two people. In response, the legislature created the Wildfire Resiliency Code Board in 2023, and local governments across the Front Range have been adopting the resulting code.

If you own a home on the western or southern edges of the metro, it may affect your next roof, siding job, deck, fence or landscaping project.

Who's covered

The state rules apply to property within the wildland-urban interface that's subject to a fire intensity classification of low or greater on the state's mapping. Local governments adopt and enforce the code, and some go further. The Resiliency Office notes that Arvada chose to be more restrictive than the state map, including areas mapped as lower risk, based on its fire chief's feedback.

To find out if your property is covered, check your city or county's wildfire code page or call the building department. Don't assume you're exempt because you're in a suburb.

Where it's in effect around Denver

• Jefferson County: wildfire resiliency code in effect July 1, 2026 for unincorporated areas.
• Douglas County: adopted a wildfire resiliency code effective July 1, 2026.
• Arvada: adopted its own code, largely referencing Jefferson County's.
• Lone Tree: publishes a list of triggering projects (below).
• Boulder: its Wildland-Urban Interface code applies as of August 1, 2025.

Other cities are adopting codes on their own timelines.

What triggers the code: Lone Tree's list

Lone Tree's page is one of the clearest. In mapped areas, the city says these activities require a permit and must meet the code:

• Constructing new structures.
• Installing new landscaping, planting new trees or altering existing landscaping.
• Building new fences or retaining walls.
• Additions or alterations that add or alter 500 square feet or more of an existing structure.
• Replacing or repairing 25% or more of an existing roof.
• Replacing or repairing 25% or more of existing exterior walls.

Lone Tree lists exemptions too, including interior renovations, and painting or staining exterior walls without removing or replacing wall materials, and some small detached accessory structures.

Defensible space zones

Jefferson County divides defensible space into three zones measured from a structure:

The areas closest to structures need the most mitigation, with less vegetation and fewer flammable materials. Jefferson County notes that decks are considered structures for these purposes. Defensible space is required only within your own property lines.

Jefferson County says the code isn't retroactive: it applies to new buildings and to certain work on existing ones. For re-siding projects that require structure hardening, only zone 1 (0–5 feet) standards apply, and the county allows a property owner self-inspection option for that zone. It also says no defensible space is required for re-roofing.

What it means for common projects

Re-roofing. Over the trigger threshold, the roof assembly must meet the code's fire-resistance requirements. Many common materials can comply; ask your roofer. See our roofing guide.

Re-siding. Expect ignition-resistant materials and zone 1 clearance. Fiber cement and other noncombustible sidings are common choices. See our siding guide.

Decks. New decks and deck replacement may need ignition-resistant materials, and the area under and within five feet of the deck matters. See our decks guide and composite vs. wood decking.

Fences. Combustible fences attached to the house can carry fire to it. In Lone Tree, new fences in mapped areas require a permit, so check the rules before you replace one.

Before you start a project

1. Check the map. Confirm whether your lot is in a covered area with your city or county.
2. Ask at the permit counter. Describe the project and ask whether it triggers wildfire code review.
3. Ask your contractor. Ask what products they'll use to comply and how compliance is documented.
4. Plan the landscaping. Zone 1 rules affect mulch, plants and anything stored against the house.
5. Check your HOA. HOA design rules still apply, and colors and materials may need approval.
6. Talk to your insurer. Some insurers ask about mitigation work, so keep records and photos.