Skip to Content
Climate change and energy

The quest to build wildfire-resistant homes

With climate change making more communities vulnerable to fire across the world, adaptation may require more social change than materials engineering.

April 18, 2023
An aerial view of the burnline at the edge of The Crosby.
In 2007, the Witch Fire burned 1,125 homes in San Diego County. But when the firestorm hit the edge of a development named The Crosby at Rancho Santa Fe, not a single house ignited.Don Bartletti/Los Angeles Times via Getty Images

The first sparks that ignited in the Montecito hills above Santa Barbara, California, on November 13, 2008, were stoked by ferocious sundowner winds gusting at up to 85 miles per hour, pushing the flames down into the densely populated canyon. Troy Harris, then the director of institutional resilience at Westmont College in Montecito, rushed from the other side of town to the campus, nestled in foothills dense with chaparral and eucalyptus. Within minutes of entering the canyon, the Tea Fire had already reached the school. But the students did not evacuate. Westmont, with a legacy of large canyon wildfires over decades and only two winding roads as routes of escape, had planned for just this kind of disaster. They stayed put.

“We had parents calling the sheriff’s office and the sheriff’s office was telling people—incorrectly—tell your kid to get out of there,” says Harris. In fact, there would have been no way to move 1,000 people down the hill faster than the fire was moving in on them. Instead, students and staff gathered in the fire-resistant gym on the southwestern corner of campus. 

Nine structures on the campus burned, but the sheltered students were unharmed. It was, says Harris, “a spectacular win,” but a highly unusual one.

With each devastating wildfire in the US West, officials consider new emergency management methods or regulations that might save homes or lives the next time. In the parts of California where the fire-ready hillsides meet human development and where the state has suffered recurring seasonal fire tragedies, that search for new means of survival has especially high stakes. Many of these methods are low cost and low tech, but no less truly innovative. With climate change bringing more communities under wildfire threat across the world, adaptation may require more social change than materials engineering.

“When people think of wildfire, they think of getting away as quickly as possible, right? Like that’s the messaging that everyone hears—evacuate, evacuate, evacuate,” says Jason Tavarez, Harris’s successor at Westmont. “And that’s 99 times out of 100.”

But the other scenario is this: a conflagration too fast and violent to escape, with no better option than to hunker. It is a “shelter in place” or “stay and defend” approach to wildfire. Evacuations from western US wildfires have routinely caused significant casualties themselves, with fleeing people trapped on narrow roads behind debris or in traffic jams. For that reason, coupled with the more destructive pace of recent fires, there is a new spotlight on the shelter-in-place strategy. Despite some notable successes, however, it is not very popular.

“In the US it’s something people are struggling to wrap their heads around,” says fire researcher Crystal Kolden, a professor at the University of California, Merced. “When is it okay to shelter in place? And more importantly, what is the minimum need in terms of the facility, and how do you do that risk-benefit trade-off in a moment of crisis?”

In order to effectively live with fire, we can build places that are easy to escape from or places that are easy to defend. These are by no means mutually exclusive, but the US West hasn’t done either. Meanwhile, the population has grown into the spaces on the rural edges of cities and suburbs, in the foothills and canyons and drainages where fire lives—what’s called the wildland-urban interface. While fires have grown in size and destructiveness over the past two decades, so has the population in these hazard areas—roughly doubling between 1990 and 2010, with the more dangerous areas growing the most. In fact, the wildland-urban interface is the fastest-growing land-use area in the US. 

Sheltering is not passive but active, whether it involves advance preparation in open-air safety sites and enclosed buildings or, in some cases, fire defense as the flames move in. In rural areas with few routes in or out, a shelter-in-place plan can mean the difference between life and death in the face of a fast-moving fire. It means planning for a worst-case scenario but not a truly rare one: a fire that moves faster than one can flee. That is the kind of fire California has seen time and again. 

In response to the increasing threat, some institutions and communities are taking a cue from Australia, where officials have employed a policy of “leave early or stay and defend” since the 1990s. But even Australia has had second thoughts since the 2009 Black Saturday fires, when more than half of the 173 people killed had been sheltering inside a home. And for the most part, the US has been slow to adopt shelter-­in-place policies for wildfire. The optics are not good—even the best-laid plans can look like abandonment or imprisonment, like leaving people to nature’s violent whims. Fire researchers and officials can’t agree on the science that should guide the planning. And with little adoption, there is little data on how well the approach works. Experts point repeatedly to the same handful of success stories like the one at Westmont College.

“We have to get over this idea that it’s always the best thing to actually evacuate,” says Kolden. “We used to have community bomb shelters, right? These are functionally community fire shelters. Those are the sort of conversations that we haven’t had. And if we really want to build fire-­resilient communities, we have to have those going forward.”

Our shelters

The basic science of preventing a building from burning is not especially high tech or expensive, but it is counterintuitive to how we have long thought about wildfire. In the 1970s, when Jack Cohen pioneered the concept of “defensible space,” a zone cleared of flammable vegetation or other fuel around a structure, the US Forest Service largely ignored him. It was a paradigm-shifting innovation—an easily implemented retrofit, at least wherever the space was available—but it meant considering wildfire from a defensive position instead of the offensive one the Forest Service had adopted for nearly 100 years. 

Today regulators have come around, and California building standards for wildland areas at high and very high fire risk now require 100 feet of open space around structures, at least where there is 100 feet available to clear. Other home-hardening measures are comparably small scale, even cheap: replacing flammable roofs, closing window seams and junctions, using fine wire mesh to cover vents where sparks might enter. And the latest fire-resistant materials won’t save a house where the gutters have been allowed to fill with dry kindling. Form tends to follow function: flat roofs, steel windows, clean lines that leave no harbor for a stray ember. Each devastating fire is bound to encourage a new innovation as fresh weaknesses are revealed. 

The basic science of preventing a building from burning is not especially high tech or expensive, but it is counterintuitive to how we have long thought about wildfire.

California’s strictest fire code applies only to homes in a clearly designated high-risk area (where, according to the California Department of Forestry and Fire Prevention, roughly one in four residential structures lies)—and only to those that are newly built. In Paradise, where a fire in 2018 killed at least 85 people and destroyed more than 18,000 structures, nearly 40% of homes built after 1996 survived, versus just 11% of those built before.

The incremental addition of more and denser housing in flammable dead-end canyons is a concern, says Thomas Cova, an evacuation researcher and professor of geography at the University of Utah. The space between houses, or lack thereof, is a significant predictor of whether or not they’ll burn. Building suburban infill is in many ways good housing policy for a state suffering from a severe lack of affordable homes, but it is bad land-use policy for a state with recurring intense wildfires. Still, there’s little clear incentive for local officials to prevent the construction of new homes, even ones that will increase the risk for the entire community. One more flammable structure on the hillside, one or two more cars on the road—but also revenue collected from one more property tax bill.

Extensive retrofitting of the built environment in towns and cities established nearly a century ago is essentially off the table—it is work that isn’t required under state codes, and no clear funding source is available. Even where communities are wiped out by fire, existing roads don’t fall under the purview of minimum fire regulations when it comes time to rebuild. But entirely new housing tracts are held to much higher standards. 

“I’ve always thought of shelter-in-place as a backup plan in emergencies, and it would be really wise to consider what options you might have,” says Cova. “But now, I think it’s also entering into the discussion associated with [new] development.” 

That’s especially true in light of California’s acute housing affordability crisis, which has put the state under severe pressure not only to continue building new homes but to build them on cheaper, more rural, more fire-risky land. A new guidance issued in October 2022 by the California state attorney general explicitly calls for local agencies to “avoid overreliance on community evacuation plans” and consider shelter-in-place options. 

“The conversation turns to not whether we’ll develop these areas, but how shelters are becoming part of it,” says Cova. In California, “they’re trying to chart a course where development in these areas can continue. You end up with public-safety and affordable-housing goals conflicting.” 

Stay and defend

Even among shelter-in-place advocates, there is broad agreement that it is always better to evacuate if there is the time and ability to do so safely. The problem is with wildfires that move so fast there’s no time to get out. A secondary, no-evacuation plan could mean the difference between guaranteed death and a chance of survival. It may be as counterintuitive a cultural innovation as defensible space, forcing us to look at wildfire as an even greater threat.

“We don’t have formal methods for designating safety zones for the public. But the concept has been used,” says Cova. In past blazes, firefighters have, for example, moved people to golf courses and turned on the sprinklers.

One of the first shelter-in-place successes in the US was a result of quick thinking rather than advance planning. In 2003, with the Cedar Fire whipping across San Diego, fire officials chose to lock down the Barona Resort and Casino instead of attempting to evacuate the hundreds of people inside. The fire chief parked his truck across the sole exit, “so that if anybody got the idea of leaving, they weren’t going anywhere,” says Cova. “The fire burned around the casino’s parking lots on all sides, all the hills around it. And the people just stayed there and gambled.”

Westmont College began its shelter-in-place planning that same year, at the urging of the local fire department. In 2009, just six months after surviving the Tea Fire, Westmont was threatened by the Jesusita Fire. This one was a little further away, and slower moving—so there was time to leave. That’s when Harris realized “we had a stay plan, but we had yet to develop a go plan.” In evacuating from Jesusita, “it was clear it was a multi-hour thing. There’s just no real fast way to get 1,000 people off the hill.” 

Tavarez is quick to point out that the Westmont students are not held against their will. But most everyone at the school at this point has bought into sheltering in place. And if anyone hasn’t, he says, “we explain very kindly but firmly that with the number of students that we have here, and the plans that we have in place, and the contingency that we built into how we do things on campus, this is actually a lot safer than trying to fight the fire down the hill.”

Nonetheless, college populations are easier to keep contained than other communities, and Westmont isn’t the only example. In 2018, ahead of the massive and fast-moving Woolsey Fire that burned through the Santa Monica mountains, officials evacuated a quarter-million people from their homes while Pepperdine University in Malibu sheltered hundreds of its students on campus. They were protected by wide defensible spaces, expansive irrigated lawns, and hardened buildings equipped with sprinklers. The school has had a shelter-in-place plan for decades, but some officials were nonetheless critical. “This shelter-in-place policy is going to have to be reassessed,” state senator Henry Stern told a crowd at a community meeting shortly after the fire. Even when it works as intended, choosing to stay while a fire rages is not popular public policy.

“It is just a bad plan for people to leave Pepperdine when they already are in the safest location you can be for survival,” says Drew Smith, LA County’s assistant fire chief. 

LA County fire officials reevaluate the plan annually and haven’t found it wanting. But Smith is skeptical of expanding the concept to smaller institutions or community buildings—there is not enough space in those structures for enough people to weather the extreme heat and smoke of a wildfire, he says. His measure is 50 people for 15 acres, or about four people in the space of a football field. Some state fire planners, though, use standard occupancy measurements to determine shelter-in-place capacity, resulting in a standard closer to a few square feet per person. The scarcity of data means there’s no consensus.

Fire-planned communities

Individual homes can also serve as shelters given the right conditions. In 2004, five communities in Rancho Santa Fe, an affluent, semi-rural part of San Diego County, were designed with this in mind. Thousands of homes were built to resist ignition; fire hydrants were spaced every 250 feet along roads in and around the community; a defensible zone and other open spaces such as golf courses and parks were maintained to buffer the neighborhoods from the chaparral and eucalyptus hillsides expected to burn; and homeowners’ associations were set up to enforce and maintain fire protection measures. 

Each home was considered to be built to shelter-in-place standards, with ignition-­resistant construction and materials—a cutting-edge approach for the time, though the standards have since been adopted into state and local codes. They are little fortresses of tile roofs, stucco walls, hardscape patios, and covered eaves. Early evacuation is still always the primary emergency plan, and the roads are designed to facilitate it. But the heavy fortification gives the communities—both the structures and the people who shelter in them—an extra chance to survive.

“Shelter-in-place was really a theory and it’s still a work in progress.”

Brandon Closs, fire prevention specialist for the Rancho Santa Fe Fire Protection District

“One of the core principles is that it’s community wide,” says Brandon Closs, fire prevention specialist for the Rancho Santa Fe Fire Protection District. San Diego’s building code has long been at the vanguard of fire safety—it was used as a model for the state regulations, and it is still more stringent than the state requires. 

“Shelter-in-place really was a theory, and it’s still a work in progress,” says Closs. He and others are confident in Rancho Santa Fe’s design, but the communities haven’t yet been thoroughly tested by a blaze. 

And nearly two decades after Rancho Santa Fe was built, it is still an outlier in the state.

Metal stools stand in the ruins left at Westmont College by the Tea Fire in Montecito, California
Nine structures on the Westmont College campus burned as the 2008 Tea Fire swept through Montecito, California. But students who sheltered in fire-resistant structures were unharmed.

Cost alone is one likely hurdle. The nonprofit Insurance Institute for Business and Home Safety estimates it costs 4% to 13% more to build a home to the highest level of fire safety, far exceeding current state standards. But achieving the level of community hardening now in place in the wealthy, gated neighborhoods of Rancho Santa Fe requires a much larger investment. 

Homes in these developments are priced in the low millions at the least: a 2,400-square-foot three-bedroom house in Rancho Santa Fe sold for $3.2 million in 2022. Lower-priced homes and communities in equally fire-risky parts of San Diego County, and across California, have none of this protection. Many homeowners in the area are also covered by insurance policies that offer private mitigation or firefighting services from their own or contracted fire crews—or at least they used to be. Even in perhaps the best-designed fire-ready wildland community in California, insurance companies are canceling policies to reduce their risk load. “The dollar is going to move a lot of things quicker than regulations can,” says Closs.

A cultural shift

It is infinitely easier to upgrade one’s own roof or vent mesh than it is to implement community-scale hardening measures. The factors making California’s wildfires more acutely destructive to people and their homes are more socioeconomic than they are climate driven.

“We’re not accustomed to thinking about what shelter-in-place looks like, because the term is most commonly associated with people’s individual houses,” says Kolden. Preparing for fire is in many ways treated as an individual problem, with homeowners responsible for their own go plans and for the full cost of any hardening measures or landscape management. This also makes wildfire a deeply unequal problem: some high-risk areas are filled with multimillion-dollar homes surrounded by plenty of open space, whose owners have the means to keep them updated with the latest construction innovations, while others are packed in on small lots overgrown with trees that residents can’t afford to cut down. Every step toward putting the burden of safety at the community level relieves some of that inequality.

“Civilization has always progressed based on community cooperation,” says Kolden. “And we need to do this for fire to have any chance of averting a lot of the disasters that we’ve seen the last few years as we move forward.” 

Deep Dive

Climate change and energy

AI is an energy hog. This is what it means for climate change.

How worried should we be about AI’s effects on the grid?

How fish-safe hydropower technology could keep more renewables on the grid

Natel Energy is trying to design turbines that are safer for fish passing through.

Google, Amazon and the problem with Big Tech’s climate claims

How companies reach their emissions goals is more important than how fast.

Here’s the problem with new plastic recycling methods

Technology is giving us more options for plastic waste, but new methods are still far from perfect.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.