In June, 2012, hundreds of homes in Mountain Shadows, Colorado, a subdivision in the foothills of the Rockies, were reduced to ash during the wind-whipped Waldo Canyon Fire. On a cul-de-sac called Hot Springs Court, however, four dwellings somehow remained standing. The mystery of their survival nagged at Alex Maranghides, a fire-protection engineer at the National Institute of Standards and Technology (NIST), who worked with several colleagues on a meticulous reconstruction of the fire. How did the homes make it through? Was there something special about them—a fireproof roof, say, or a fancy sprinkler system?
The team collected weather reports, topographic data, G.P.S. records from fire engines, photos, videos, and property-damage reports. They debriefed more than two hundred witnesses, mostly first responders. After a hundred and fifty “technical discussions,” Maranghides finally met two firefighters from Northern California who were able to explain the miracle at Hot Springs Court. Their crew had parked their fire truck there and, for an entire night, had hosed down the four houses. (A fortuitous change in the wind helped, too.)
After a catastrophic fire, speculation about “miracle homes” is almost irresistible. But the NIST case study showed that an observer can’t reliably decipher the reasons that certain houses survive by examining the dwellings alone. “Unless you have video footage and firsthand information, when you see a home that’s standing, you cannot say why,” Maranghides told me. In multiple studies of such disasters, his team has found that, on average, ninety per cent of damaged but standing houses were saved not so much by savvy design and construction choices but instead by firefighters’ actions.
As researchers have started to demystify fires in the so-called wildland-urban interface, or WUI (pronounced “wü-ē”), which are the middle ground between developed and undeveloped terrain, they have overturned a multitude of assumptions about why some houses burn and others do not. For example, homeowners often expect fires to spread from forests into residential areas via an advancing wall of flames. But experts long ago observed that wildland blazes throw off embers, which can soar on winds to ignite dwellings miles away.
Such revisions in the conventional wisdom force us to rethink how we protect ourselves. In the late twentieth century, fire agencies urged homeowners to replace flammable wooden shingles with alternatives such as Spanish tiles, which are made from non-combustible terra-cotta. But when Maranghides and his colleagues studied the 2007 Witch Creek Fire, in San Diego, their fieldwork and lab research indicated that embers frequently snuck beneath the terra-cotta, ignited dead leaves, and set underlying plywood alight. They concluded that embers were involved in starting fires in about two-thirds of the destroyed homes. (California’s building code now requires contractors to plug the gaps underneath curved tiles; some fixes for fires need fixing themselves.)
WUI conflagrations are wickedly complex, but scientists have been inching toward a sort of unified theory for prevention. In a 2022 report, Maranghides, his NIST colleagues, and co-authors at two partners, Cal Fire and the Insurance Institute for Business and Home Safety (I.B.H.S.), compiled all the known ways—upwards of fifty—by which embers, flames, or their radiant heat might set a house ablaze. It also outlined how property owners can retrofit entire neighborhoods to block every single ignition pathway. Roofs should be made from “Class A”-rated fire-protective materials; wall vents should be covered with fine wire mesh; eaves should be closed so that flammable beams aren’t exposed; windows should be made from double-paned tempered glass, which is less likely to shatter from heat. Something as simple as a seal around a garage door can keep embers out. Although such recommendations take time to trickle into state regulations, a number of them appeared in a building code that California enacted in 2008, Chapter 7A, which set unprecedented standards for new houses in the most fire-prone areas.
But the new paradigm for fighting these fires contains an inconvenient truth. Most people don’t live in new houses, and most building codes aren’t as strict as California’s. And so, for the large majority of the approximately fifty million U.S. homes in the WUI, fire prevention falls to individual homeowners—it’s voluntary and ad hoc. “The approach that has been taken for the last quarter century has been one of, ‘Hey, something is better than nothing,’ ” Maranghides told me. “And, from a fire perspective, that is absolutely not true. Fire doesn’t work that way.” A homeowner could complete eighty per cent of fire-protection measures, potentially spending many tens of thousands of dollars on retrofits, and lose their house because of the twenty per cent that remains unfinished—in no small part because of uncontrollable, unpredictable embers.
This reality has led Maranghides to a position so logical that it reminded me of Spock, the ultra-rational character from “Star Trek.” For homes to survive fire disasters on their own, he said, people who live on the boundary with wildlands should not only clear sources of fuel from around their properties but also make a hundred per cent of potential home-hardening improvements. Even these extraordinary measures, he went on, are insufficient. No home is an island, and dense housing developments can protect themselves only if every neighbor does the same work. Such recommendations are so stringent that they may seem impossible; some of Maranghides’s colleagues in the fire-prevention world worry that the message will deter the public from trying. “You cannot pick and choose,” Maranghides told me. “The science tells us you have to do everything.”
For much of the twentieth century, forest fires tended to threaten rural communities. Over time, a particular approach to fire prevention emerged: if your house sat on a spacious parcel in or near the woods, you could work to protect it by creating a buffer around it. In the sixties, a California law supported by the state’s fire agency advanced the foundational concept of defensible space, a zone of up to a hundred feet where fuels such as brush and trees are strategically trimmed back and managed. The U.S. Forest Service eventually recommended the practice. But, throughout the decades, housing developments crept toward wildlands, the climate warmed, and fires increasingly escalated into unstoppable urban conflagrations. In the past decade, California’s most destructive fires incinerated more than fifty-seven thousand homes, commercial properties, and other structures. And, when the nearest source of fuel is not the woods but, rather, the house next door, a broader strategy is needed. Houses had to be hardened to make them less likely to go up in flames.
This past spring, I visited Maranghides at the National Fire Research Laboratory, which studies hardening strategies in a hulking, warehouse-like structure on NIST’s campus in Gaithersburg, Maryland. Enormous ventilation pipes were coiled like snakes on the roof of the building. Maranghides, bespectacled and in jeans, met me in the vestibule, where we grabbed white hard hats. From there, we entered a cavernous room with a reinforced concrete floor. A roughly fifty-foot-square air-exhaust hood—an industrial version of what one finds in home kitchens—hung from the ceiling.
A dozen researchers were gathered around a mockup of a single-story dwelling. A beige façade made from cement fibreboard featured a double-pane slider window, an asphalt-composite shingle roof, and a metal gutter. It was designed to be highly fire-resistant, in keeping with Chapter 7A and the International Wildland-Urban Interface Code. (The house was like a stage set, with scaffolding where the other three walls would have been; sensors tracked metrics such as temperature and heat flux.) But all eyes were focussed on a small shed made from corrugated steel sitting five feet from the house. Its open door, facing the dwelling, revealed stacks of wood inside.
“Stand by for ignition,” a voice announced through a loudspeaker. A man in firefighting gear approached the shed, used a propane torch to set a fire, and walked away. Within minutes, an incandescent blaze was shooting out the door toward the wall. We could hear loud crackling; embers flew about. Soon, orange-red flames began to lick the wall and the roof’s open eaves. Smoke spiralled upward. The window frame, which was made from white vinyl, started melting and then ignited. Around ten minutes into the experiment, the eaves were burning. A glass window pane fell to the ground.
“Fire out!” a supervisor yelled. Firefighters doused the flames, generating clouds of steam.
“You see how quickly it happens?” Maranghides said. Even a hardened home has weaknesses—in this case, a flammable window frame and unclosed eaves—that can lead to failure. “Even 7A has significant limits,” he said. Many of NIST’s recommended retrofitting measures have not yet made it into WUI building codes.
The experiment that I witnessed was part of a series examining, in part, the role of sheds in fires. The researchers had also identified wooden gazebos, decks, mulch beds, recycling bins, play sets, cars, and R.V.s as crucial but overlooked sources of fuel. In the L.A. fires, such hazards helped fires hopscotch across neighboring lots, according to a rapid I.B.H.S. assessment. NIST recommendations increasingly address mutual dangers; a homeowner might place her gazebo at a minimum distance from her own home and that of her neighbor, and park her car in the garage.
Maranghides told me that the idea of defensible space has at times become part of the problem. On tight real-estate parcels, people may move sheds or firewood out to the property line—closer to the neighbor’s house. Attempting to create buffer zones in this way “does not work when you don’t have space,” he said. “It actually makes things worse.” While investigating the 2018 Camp Fire, he and his colleagues learned of a shed that went up in flames in a corner of a back yard, far from the owners’ four-bedroom stucco house. The blaze leaped to a nearby wooden fence and a neighbor’s shed, which exploded and injured a firefighter. Afterward, aerial photos showed the first residence still intact, but the neighbor’s home was rubble and ash. “Fire doesn’t care about who owns what,” Maranghides said.
Unfortunately, the communal nature of fire dangers isn’t always emphasized in the guides given to the public. While writing this story, I found that online advice often featured illustrations of a single abode on an isolated parcel. And, though Cal Fire’s home-hardening tips warned about “accessory buildings” and “miscellaneous structures” such as sheds, play sets, and R.V.s and explicitly cautioned against moving them next to neighboring residences, such issues were not mentioned on a wildfire-prevention webpage promoted by the nonprofit National Fire Protection Association (N.F.P.A.) and its educational program, Firewise USA.
The science shows that fire resilience can only be built in a coöperative way. “We need very, very significant, fundamental paradigm shifts in how we build, how we live, how we maintain,” Maranghides told me. But his uncompromising message on retrofitting may be difficult to hear. “It’s much better to ‘do everything’ if you can,” Alexandra Syphard, a senior research scientist who studies wildfires at the Oregon-based nonprofit Conservation Biology Institute, told me. But “the message that one could take from that statement is that, ‘Oh, well, I can’t afford to do everything. Therefore, I’m going to do nothing.’ ” Stephen Quarles, a former I.B.H.S. scientist who co-authored the 2022 NIST report, agreed with Maranghides that the eighty-twenty rule of disaster preparedness doesn’t work on wildfires. But “it can be discouraging to emphasize that,” he said. Quarles favors giving homeowners a shorter, tailored list of the most important retrofits to prioritize, and then work through other items down the line. “They can sort of bite them off in manageable chunks,” he said.
The essential dilemma is that there are no quick or simple fixes for making millions of older homes fire-safe—and few levers for forcing owners to take on the challenge. Voluntary retrofitting can be more productive than imposing an unpopular mandate, Michele Steinberg, the wildfire director at N.F.P.A., said. “We’ve had to walk that line,” she said. “How much is too much to ask people before they throw up their hands and say, ‘We don’t want to do this’? And how much is not enough?” The N.F.P.A. recently argued for public policies that would require every building in the WUI, even old ones, to be fire-resistant. But, right now, neighbors must volunteer just one hour per household per year to maintain a Firewise community group; the designation may earn them discounts on California home insurance. “We need to push for much better,” Steinberg acknowledged. “But how, in our cultural context, do we get it done?”
It’s difficult to imagine a nationwide solution for WUI fires that doesn’t include vast investments in home hardening by the federal and state government. This would require political will and buy-in from homeowners. “The long game is really the goal,” Maranghides told me. The public needed a generation to accept automobile seat belts and tornado shelters; new safety standards had to be met with changes in the culture. “All these things, they take time to move through society,” Maranghides went on. He worries about how many more homes will burn before people are protected.
California remains vulnerable to devastating fires, but recent developments there help one imagine the path toward a more comprehensive and communal fire-prevention strategy. A controversial state law will soon mandate that combustible materials be cleared out of the five-foot perimeter around any dwelling in fire-prone neighborhoods. (The rules, which are known as “Zone Zero” regulations, could be finalized this year.) Meanwhile, a more holistic experiment called the California Wildfire Mitigation Program (C.W.M.P.), a hundred-and-seventeen-million-dollar pilot initiative, is aiming to harden about two thousand homes across six low-to-moderate-income communities. Largely funded by the Federal Emergency Management Agency, it aims to simplify the home-hardening process, and its minimum quality standards incorporate NIST’s 2022 guidance and Zone Zero measures. More than seventy dwellings have been completed so far.
These efforts may offer a preview of what countless neighborhoods will eventually face. Jose de Jesus (J.) Lopez, the executive director of the C.W.M.P. Authority, told me that the program’s maximum retrofitting budget tends to fall between sixty thousand and seventy-five thousand dollars per home. At that price, he said, “perfection”—as in, full retrofitting—“is very hard to achieve.” Susanne Bach, who lives in a hilly community in Kelseyville, California, told me that a local nonprofit spruced up her family home with funding from C.W.M.P. and her county. Unfortunately, six-foot-tall brush is growing in undeveloped lots nearby. If it ignites, wind could drive embers onto their roof—which isn’t fire-resistant and wasn’t within the scope of the upgrades. Then, Bach fears, “all that work we did isn’t going to matter.”
In August, 2024, Kate and Michael, a retired couple in Oakland, California, learned their home-insurance policy was being cancelled; their ridgetop neighborhood is largely surrounded by regional parkland that is at high risk of fire. A representative from the insurer referred them to a voluntary home-hardening program that certifies residences as “wildfire prepared.” (The requirements, which were developed by the I.B.H.S., include most of the recommendations from NIST.) If they were certified within ninety days, their policy might be renewed. “There’s no way we could do that,” Michael told me in a phone call.
They obtained coverage from another insurer. Then, anxious about losing their insurance again this summer, they spent about fifteen thousand dollars on improvements to their residence—which already had a metal roof, double-paned windows, and ember-blocking wall vents. They put in new metal gutter covers and ripped out fire-prone rosemary bushes. They removed nearly all plants from their Zone Zero perimeter and swapped out mulch for gray gravel. They replaced two wooden gates that were attached to the house with stylish black metal ones.
At one point, I told Kate and Michael about NIST’s rigorous retrofitting philosophy, and I e-mailed them a link to the C.W.M.P.’s standards. The next time we spoke, Kate sounded deflated. “There’s just a lot,” she said. “It always comes back to, ‘Well, do you want your house to burn?’ I don’t. Am I supposed to put another hundred thousand in it that I don’t have?”
“It’s so overwhelming to everybody,” Michael said. “And then your immediate reaction is, ‘Screw it, I’m not gonna do anything.’ ”
A few days later, on a bright May afternoon, I drove up to their one-story house, which had a stucco front exterior in a pleasant yellow hue. Wind chimes rang out in the back yard, which brimmed with pointy succulents, low-lying shrubs, and a few small trees. The couple showed me major retrofits that they were still aiming to address. They had to decide what to do with their tropical-hardwood decks, and whether to upgrade some old siding. They’d found online resources that gave conflicting information on the best way to close their open roof eaves, which was frustrating. And did they need to move two small plastic storage sheds that sat against the house?
Kate and Michael have been helping to start a local Firewise group, but recruitment is slow. I asked them whether they could imagine working with neighbors to address potential hazards such as sheds and gazebos. “It feels impossible,” Kate said. “All we can do is educate on what are the risks. But you can’t tell people what to do, right?” They are in their seventies; standing in their driveway, they told me that it will take several years to do all the retrofitting they can afford. “I think we’ve learned to take it in chunks,” Kate said. “Get some stuff done, and then take a little break. Reëvaluate everything with new information that comes along.” In mid-June, they were relieved to learn that their home insurance would be renewed—but their annual premium was going up by a thousand dollars. ♦
An earlier version of this article misstated the dimensions of an air-exhaust hood in the National Fire Research Laboratory.