The risks—and solutions—to living in the Wildland Urban Interface.


TWildland-Urban Interface is a crucial boundary where human development converges with nature. Big Sky, Montana sits in this zone with its structures prone to wildfire and extreme weather conditions.

“We don’t live in an environment that most of the United States lives in,” said David Dexter, chief executive officer at Cornerstone Management Services. “We are very unique. We have a lot of snow. We now have a lot of fire danger. It’s that weird dichotomy. And a lot of people in the United States don’t even have one
of those.”

In Big Sky’s early years, construction of homes and businesses did not include planning for building in the Wildland- Urban Interface (WUI), which was nothing more than an afterthought. Today, the Big Sky community and local businesses have taken a more active role in preparedness through compliant building practices, forward-thinking planning and investment in research into WUI-compliant building materials to improve resilience against the ever- looming threat of wildfire.

“I think that we as builders, humanity, oftentimes in 20 years look back and think ‘Crap, I can’t believe we did that,’” Dexter said. “Trying to get that view into the future, understanding what implications 20 years down the road will be, so we can plan for it now, so it’s not something that catches us off guard.”

Cornerstone Management Services (CMS) in Big Sky has put in time and research, as well as collaboration with students in Montana State University’s engineering department, to develop the best WUI-compliant building practices, materials and efficiencies to mitigate wildfire risk.

Wildfires in the West are getting larger and more dangerous, and more people are moving to the WUI, lowering the bar of vulnerability.

“We’ve all seen the differences between winters, from last winter to this winter, and even the one previous where we had the Yellowstone [River] flood,” said Teran Foster, research and development manager at CMS. “So, there’s different precipitation that is happening every year, so it’s not consistent. That also creates this drastic potential for wildfires. Again, we’ve all seen it. We’ve all breathed that smoke. But Wildland-Urban Interface is a great starting point and standard.”

Building in the WUI is a matter of dealing with the potential for wildfire, as well as the potential for significant snowfall. Ice damming on roofs is a constant consideration for homes in the WUI, and cold roof systems have become the best way to combat this. CMS has developed a cold roof system designed and tested for the Big Sky environment that reduces ice damming; prevents condensation build-up; reduces heating and cooling costs; and provides prolonged life expectancy of roofing materials.

And on the flip-side is fire. A home burning down is the process of structural ignition. Focusing first on the structure of a home, the building materials need to be assessed. Historically, wood products unsurprisingly burn under enough heat or exposure from wildfire. Wildfire- resistant building materials can include materials like metal and asphalt.

“We know a great deal about how to build smarter, durable, more sustainable homes in high-risk areas,” said Kimiko Barrett Ph.D., wildfire research and policy lead at Headwaters Economics. “We know from decades of research, laboratory experiments, and post- fire analyses that building materials, structural design and neighborhood layout are critical determinants of a home’s survival from a wildfire. So it is really a scale issue because it has to occur at all scales.”

The near home combustible zone is absolutely critical. This zone is zero to 5 feet from the home itself. This is generally the region where people would keep their flower beds, for instance. When one home starts to burn, it gives off radiant heat and, as the house itself becomes a source of fuel, threatens surrounding structures.

The key factors when considering designing a home in the WUI are ignition points, layout of the land or neighborhood, building materials, landscaping and vegetation.

“Vegetation management I don’t think has been done quite effectively here [in Big Sky], where there’s trees and dry brush or even just firewood that’s stacked up against the housing,” Foster said. “Our largest hope is to be able to have that fully WUI-compliant exterior to protect these homes and then also have the vegetation management done properly.”

Bark mulch is incredibly popular in Montana and in many parts of the country, but is highly flammable because it covers a wide surface area and is often chemically treated. Replacing materials like bark mulch with gravel can aid in wildfire resistance.

“Unlike the common media narrative of a wall of flames that comes down a mountainside and burns a community to the ground, what in fact is the primary culprit of home loss are embers,” Barrett said. “Embers can fly. What we’re talking about are the little fireballs that launch themselves out of a campfire, for instance. And yet this is obviously at much larger scale with a wildfire. But they are these balls of flames, also known as firebrands. They launch themselves anywhere from 1 to 4 miles ahead of a wildfire front.”

If embers land on any flammable surface area, they can grow in size and intensity to become a spot fire. The spot fire will then propagate wildfire spread from a home into a community. When considering a home’s vulnerability to wildfire, one must consider embers and any exposed surface area that can ignite.

“It’s not just a roof. It’s also the valleys of the roof where embers can accumulate,” Barrett said. “If there’s pine needles in that roof valley, they’ll ignite the pine needles or what’s in your gutters. If you have vegetation and debris within your gutters, you must think about working your way down from that decking surface areas, often made of wood. Very often on the surface of the deck is a lot of flammable furniture or materials, like firewood, like furniture itself, propane tanks. Things like this, all of which are vulnerable ignition points. If you have a house that has wood siding, that is another exposure and vulnerability, especially if you have a lot of vegetation or plants built up against the home as well.”

CMS in Big Sky provides construction and remodel services to clients building in the WUI, as well as offering guidance regarding vegetation management; roofing; venting; exterior coverings; decking; exterior windows and doors; and more. In addition to being a supplier and operating business however, wildfire safety is a personal matter, as many of CMS’s employees live and raise their families in Big Sky.

“Our overall mission is to protect and progress our communities,” Dexter said. “We’re trying to do that by really redefining that exterior building envelope, but really, instead of looking at just one piece of the puzzle, looking at that holistic picture at the same time.”

One important design consideration on a home, Barrett explains, are the eaves. “By enclosing your eaves with a non-combustible soffit, for example, you are preventing that heat trapping from occurring where you would have embers penetrate through the attic vents or in through the soffit,” Barrett said. “It’s little things, as well, when you talk about the exterior of a home that’s vulnerable. You’re talking about the roof, the eaves, the exterior wall, the deck, and the non-combustible zone. And then windows and doors are also vulnerable points.”

Many homes in Montana are being built in wildfire risk areas, with an increase in building in these areas during the pandemic. The risk of wildfire is going up significantly each year and the responsibility and accountability is on the individual homeowner to consider that risk.

“Mitigation has to occur at scale,” Barrett said. “What we know is that one homeowner can fully mitigate his property and his structure, but if his neighbor does nothing, then his house is still at risk because of how wildfire ignition occurs and radiant heat threat.”

“This is going to become part of the challenge that homeowners face in Montana, particularly not with just increasing risk, but for insurance, which is going to become a very real concern for many of us in the not too distant future,” Barrett said. “It already is for some.”

Montana does have a Wildland-Urban Interface code that was adopted from a national model and explicitly addresses wildfire. Theoretically, this model code isn’t intended to address wildfire construction in high-risk areas; when Montana adopted this code, legislature stripped it of anything regulatory in nature. State government in Montana tends to be anti-regulatory and does not want pushback from the construction industry. By watering down this code, the state does not allow local jurisdictions, towns or counties to adopt anything more stringent than what the state has already adopted.

“What the state has done has really prohibited and limited the abilities for local jurisdictions to regulate through a WUI code or a building code,” Barrett said. “But it is needed for reducing risk at scale. It is the only measure that works because of the compliance mechanism behind it.”

Currently, Montana is hamstrung at the state level, and until that is overturned, local jurisdictions do not have a lot of authority to implement strong wildfire resistance measures.

“I just want to make sure that readers know that building to wildfire resistance standards does not mean you need to have affluence, wealth or access to highly specialized materials,” Barrett said. “That’s not true. These are widely available materials, and they can be quite cost affordable.”

Taylor Owens is a writer who spends her days running in the sun, playing in the snow, or on the hunt for the best breakfast across the West. She is based in Bozeman and is the content marketing lead at Outlaw Partners.