Three years after the Marshall Fire left Boulder County in shock — destroying more than a thousand homes and upending the lives of thousands of residents — a new level of urgency is shaping the conversation around protecting homes from future wildfires.
The City of Boulder is now considering, for the first time, expanding its definition of the wildland-urban interface (WUI) — the areas most at risk of wildfire — and introducing a mandate that would require existing homeowners in those zones, not just new construction, to implement fire mitigation measures. If adopted, the proposals would mark a significant shift in how the city approaches wildfire preparedness, putting more responsibility on residents to safeguard their properties.
In the City of Louisville, where scars from the Marshall Fire remain fresh, a new ordinance already took effect this month. Now part of the building code, the new regulations require home and business owners to implement wildfire-resistant hardening measures. The law went into effect on Dec. 10, following unanimous approval by the city council in November.
Ordinances for home wildfire resilience exist elsewhere in Colorado. Aspen has required ignition-resistant construction since April 2023, while unincorporated Eagle County has required developers to incorporate home-hardening measures since 2003. On the Front Range, all homes within Colorado Springs must have fire-resistant roofing, along with additional home-hardening and fuel mitigation requirements for homes in the wildland-urban interface. House Bill 1091, passed last year, bars HOAs from prohibiting home hardening. California, meanwhile, has mandated wildfire building codes in high-risk areas for over a decade.
Louisville’s ordinance applies to new construction and certain renovations to existing buildings, such as adding new structures or material replacements, but exempts already-permitted homes being rebuilt after the Marshall Fire. That exemption, made to save costs for underinsured residents struggling to rebuild, raises questions about the ordinance’s overall impact, given the hundreds of homes under reconstruction. Still, all building permits, including those for Marshall Fire home rebuilds, received on or after Dec. 10 will be subject to the ordinance.
Requirements include Class A fire-resistant roofing — such as metal, clay or concrete — that offers the highest fire resistance; ember-resistant vent screens no larger than one-eighth of an inch; metal gutters with guards; and non-combustible siding, decks and fences within five feet of a home to create “defensible space,” a buffer to slow or stop wildfire spread by reducing nearby flammable materials.
“Following the Marshall Fire, there has been a fair amount of community feedback wanting the city to consider some type of home-hardening code to help the city be more resilient if there was to be another wildfire,” Louisville’s Community Planning Director Rob Zuccaro told Boulder Reporting Lab.
The Facilitated Learning Analysis (FLA) for the Marshall Fire — a state government report combining analysis and commentary — highlighted the role of wooden fences in worsening the destruction. Those structures burned hotter and longer than grasses, and more homes with wooden fences were lost compared to homes where lawns acted as buffers. Wind-driven embers were another significant factor, as they ignited flammable structures wherever they landed.
The new requirements aim to address these vulnerabilities. For example, ember-resistant vent screens prevent fiery embers from entering homes. Double- or triple-paned windows, previously mandated as part of Louisville’s energy code, are also meant to improve wildfire resilience by reducing the likelihood of breakage under extreme heat, also preventing embers from entering a home.
John Willson, fire chief of Louisville’s Fire Protection District, said work on the ordinance began about a year after the Marshall Fire.
“We might be taking a little bit of the credit, but it was a lot of hard work by a lot of different people that got this ordinance through,” Willson said, crediting collaboration between residents, city council and local departments.
Willson estimates the home-hardening requirements will increase construction costs by around 5%, but he emphasizes the long-term savings, noting also that many of the materials are also hail-resistant, reducing maintenance expenses.
“It might cost more upfront, but probably in the long-run, it will not, and it will protect them. And insurance companies like it too,” Willson said.
Rising wildfire risks and insurance challenges
The ordinance arrives as Boulder County homeowners face soaring insurance premiums or dropped coverage due to escalating wildfire risks. Home hardening can help residents retain coverage and reduce fire spread between homes.
“And that’s even more cause for home hardening,” Willson explained, “because if you have one house that catches on fire, it can expose the house next to it.” Fire-resistant homes also allow more time for evacuation or firefighting.
The Marshall Fire, which ignited near the City of Boulder’s southeastern edge and spread eastward with 100 mph winds, challenged previous assumptions about wildfire risk in Boulder County, as the burn area was not considered part of the WUI. Louisville’s ordinance takes a citywide approach, which Zuccaro described as less stringent than rules targeting WUI zones in the Mountain West but designed to build a more resilient building stock over time.
“So if there was a wildfire or structure fire, there would be less chance there would be a conflagration fire — where it starts to spread within a neighborhood,” he said. This is a key concern with fire mitigation, as a single non-fireproofed home in a neighborhood of hardened homes can still ignite and spread fire to surrounding properties.
While homes rebuilt in the aftermath of the Marshall Fire are exempt from the new ordinance until Dec. 10, many homeowners have voluntarily chosen to use fire-resistant materials after conducting their own research, according to Willson. “Sometimes you can’t wait for the government to tell you what the right thing to do is,” Willson said. “A lot of people took it upon themselves to get educated and to protect their own property.”
While Louisville residents must cover the costs of compliance, Wildfire Partners, a Boulder County program, offers grants and rebates for wildfire mitigation. The rebate program is expected to reopen in 2025. Mitigation efforts through Wildfire Partners and county building codes resulted in a 100% survival rate for 13 certified or mitigated homes during the Stone Canyon Fire, the Wildfire Partners has said, compared to 77% for unmitigated homes.
At the state level, officials are also developing wildfire resilience standards, though these may vary depending on a community’s location and risk factors.
Correction: A previous version of this story incorrectly identified Wildfire Partners as a nonprofit organization. It is a Boulder County government program.
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