What the Wildland-Urban Interface Means in Missoula and Ravalli Counties

What is the wildland-urban interface?

Montana law defines it in the forestry statutes. Montana Code Annotated 76-13-102 says the wildland-urban interface means the line, area or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels. Missoula County's subdivision regulations, as quoted in the county's 2018 wildfire plan, use nearly the same words.

Federal guidance adds two categories. Missoula County's plan explains that the definition in the Federal Register divides the WUI by structure or population density into interface, where structures directly abut wildland fuels with a clear line between developed and wildland areas, and intermix, where structures are scattered throughout a wildland area. Both are common here: subdivisions edging onto timbered hillsides are interface, and homes on acreage in the pines are intermix.

How does Missoula County define its WUI?

Broadly. Its 2018 community wildfire protection plan defines the WUI as any area where the combination of human development and vegetation has a potential to result in negative impacts from wildfire on the community. To map it, the county adapted the Forest Service's national WUI method using county address points and its own fire behavior fuel data, and made one important change: national mapping requires at least 6.18 structures per square kilometer, about one per 40 acres, while Missoula County counts any area with structure density greater than zero.

The plan maps four classes. WUI intermix is any area with structures and at least 50 percent wildland vegetation within a 40-acre radius. WUI interface is any area with structures and less vegetation that lies within 1.5 miles of a large, contiguous wildland area, which the plan explains is within ember range. Areas with structures farther than that from big wildlands are non-WUI inhabited, and areas with no structures are non-WUI uninhabited. The earlier 2005 plan had used a simpler 1.5-mile buffer around mapped structures.

Is Missoula County updating its plan?

Yes. Missoula County's wildfire plan page says the county adopted its first plan in 2005, updated it in 2018, and is in the early stages of an update in 2026. A county news release announced public workshops in Missoula, Frenchtown, Lolo and Seeley Lake in June, said the update will use new data and address new issues such as wildfire smoke, and listed a focus on the home ignition zone and smoke readiness among its goals.

The same release makes a point many residents miss: a community wildfire protection plan is a planning tool created under the 2003 federal Healthy Forests Restoration Act, and it is not a regulation, a growth plan or an evacuation plan, though it can guide those. Check the county's page for the current status before relying on any map. Our guide to Missoula County wildfire resources lists the programs that go with it.

How does Ravalli County define its WUI?

Ravalli County completed a revised community wildfire protection plan in 2024, building on its 2006 plan. The 2024 plan defines the WUI to reflect areas at risk from wildfire and areas that would be heavily impacted by one, and builds the map from overlapping components rather than a single density rule. The listed components are structure density with vegetation, highly valued resources and assets, primary and secondary highways, ingress and egress roads, communities with critical infrastructure, utilities and communication sites, a Community Protection Zone and at-risk communities.

The buffers are generous. The plan says the federal definition and national mapping buffer each structure by 40 acres, but because most of the county is rural, every addressed structure in the county was included with a one-mile buffer, which the plan says accounts for ember spread by wind. Roads, critical infrastructure and high-voltage lines are also buffered by one mile. Wildland fuels are defined broadly to include forests, grass, shrubs, wetlands, pasture, cropland and undeveloped land. The plan notes that dense urban areas fall inside the boundary but have lower priority for fuel projects.

What is Ravalli County's Community Protection Zone?

It is a modeled zone, not a measured one. Ravalli County's plan explains that a 2019 wildfire risk assessment for the Bitterroot National Forest simulated 50,000 fire ignitions across the landscape under moderate and extreme conditions and mapped the probability that a fire starting in a given place would reach structures on private land. The county included in its WUI the areas where 50 to 100 percent of simulated fire starts would reach a private structure if suppression failed.

The plan also identifies West Fork and Painted Rocks as at-risk communities, a term from the Healthy Forests Restoration Act for groups of homes near federal land where wildfire threatens life and property, and notes that the county's maps are kept current on an online story map. Our guide to Ravalli County fire districts and resources covers who protects which areas.

Does living in the WUI mean I have to do anything?

Not by itself. Being inside a CWPP's WUI boundary does not create a defensible space requirement for an existing home; Missoula County describes its plan as not a regulation. What WUI mapping does is direct planning and money: Ravalli County's plan says delineating the WUI facilitates access to funding for projects that reduce risk, and Missoula County's says a clear WUI map will help with future land use policies that need a tiered approach.

Rules can apply in other ways. New construction and additions may face local building or subdivision requirements tied to wildfire, which is the subject of our guide to building in the WUI in Montana, and insurers increasingly look at wildfire exposure, covered in wildfire and home insurance in Montana. Our Montana wildfire laws guide sets out what homeowners are and are not required to do. None of this is legal advice; ask your county planning office or an attorney about a specific property.

If my house is in the WUI, how risky is it?

The WUI map cannot tell you. Forest Service fire scientist Jack Cohen argued in a 2000 Journal of Forestry paper that the wildfire threat to homes is not a function of where a home sits relative to wildlands but of how it ignites, and that home ignitability, set by the home and its surroundings within about 40 meters, should be the main characteristic in mapping home loss potential. He wrote that homes with low ignitability can survive high intensity fires while highly ignitable homes can be lost to lower intensity ones.

For a relative picture of community risk, the Forest Service's free Wildfire Risk to Communities website, built with the Missoula Fire Sciences Laboratory, maps how risk varies across states, counties and communities. For your own house, the home ignition zone and a free wildfire risk assessment are the right tools.

How much of Missoula and Ravalli counties is in the WUI?

Most of the inhabited land. Missoula County's plan reports that populated areas occupy about 29 percent of county land and the rest is uninhabited, and because the county counts any structure density above zero, nearly all populated land near wildland vegetation falls into one of its two WUI classes. In Ravalli County, every addressed structure is inside the WUI by definition, along with a one-mile buffer around it and around roads and utility lines.

Vegetation inside the WUI is not exotic. Missoula County's plan says dry ponderosa pine forests occupy about 36 percent of the WUI intermix area and about 40 percent of the WUI interface area, with grasslands and riparian cottonwood and aspen woodlands also significant. That is the vegetation of ordinary yards and acreages, which is why fire mitigation here is part of ordinary property maintenance.

What should a homeowner in the WUI do?

Use the WUI map to understand that fire can reach your area, then work on what decides whether your house ignites: the roof and gutters, the first five feet, fuel within 30 feet, and ladder fuels and crown spacing out to about 100 feet. Our guide to defensible space zones in western Montana lays it out, and neighborhood programs such as Firewise USA help where lots are close together.

HJ Property Care does the vegetation side through our fire mitigation service across Missoula and Ravalli counties, from Clinton and Lolo to Hamilton and Darby. This guide is part of our Montana Wildfire Guide.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate and we will walk the property with you.

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