This story was originally published by Columbia Insight.
In early August, just days after the Old Trails Fire ignited, kicking off the Spokane Complex Fires, I received an email with the intriguing subject line: “A different approach to fire-resistant construction.”
It was a well-baited hook. I bit.
The email was from a publicist working for a California-based company that makes Incablocks, interlocking concrete masonry blocks that hook together sort of like large LEGOs®. The blocks’ selling point? They’re fire resistant.
“People are afraid to rebuild with wood,” Daniel Correa, co-inventor of the blocks, told me weeks later, referring to people in Paradise, Calif., where lots still sit empty following the 2018 Camp Fire. “They really like the idea of having a masonry home that could be, not fireproof, but it would retard fire for a long time.”
Correa plans to build in Paradise. Have enough of his masonry houses in a neighborhood, he told me, and fire will be less likely to propagate from home to home.
By the time I talked to Correa, the Spokane fires were contained, but some 600 homes had been destroyed.
A major reason the fires in both Spokane and Paradise were so destructive was that, although they started as wildfires outside of town, they found their way into residential neighborhoods.
Once there, the burning homes themselves fueled the fire as embers and flames jumped from home to home. In the process, the fires transitioned from wildfires into urban conflagrations.
This dynamic has occurred repeatedly, including during the September 2020 Almeda Fire in Oregon and the 2025 Eaton and Palisades fires in Los Angeles County.
In fact, from 2013 to 2022, the lower 48 have experienced nearly twice as many destructive fires as they did from 2002 to 2012. Those fires also destroyed far more buildings, rising from 905 to 6,239 destroyed buildings per year on average, according to a paper published in the Proceedings of the National Academy of Sciences.
Following this destruction have been sales pitches for fire-resistant building materials.
But are these materials needed? As it happens, wildfire codes have already pushed builders toward them, at least for the exteriors of homes.
To comply with wildfire codes, wood-framed buildings are increasingly being “hardened” by covering them in fire-resistant alternatives, including steel siding and HardiePlank, made of fiber-cement. Wood, in other words, is starting to lose the battle for our homes’ exteriors.
The new battleground is our homes’ frames, their very bones.
More than skin deep?
For years, scientists have known that human-caused greenhouse gas emissions are making our atmosphere thirstier, drying out our landscapes, making them more likely to burn should an ignition source—be it a downed power line or a tool’s stray spark—be present, and that this process is likely to accelerate, leading to larger fires as atmospheric temperatures continue to rise.
This process is happening across the West, including in Oregon and Washington.
However, it’s in California, which has seen some of the largest and most destructive urban conflagrations in recent years, where the strongest sales pitches for alternatives to wood are being made.
The concrete industry in California has its “Building With Resilience” campaign, which emphasizes the fire resistance of concrete, masonry, metal, stone, fiber-cement and asphalt.
Meanwhile, the Steel Framing Industry Association has its BuildSteel outreach effort, highlighting how “Wood Feeds Fires—Steel Does Not.” The association is also promoting RESET, a program that hopes to build noncombustible steel homes in the Pacific Palisades to replace homes lost to fire.
In an emailed statement to Columbia Insight, a spokesperson for the American Wood Council responded: “Families rebuilding after wildland-urban interface fires deserve guidance grounded in fire science and building codes, not material marketing.”
The statement continued, noting that current wildland-urban interface building codes “don’t dictate which material a home is built from” and that wood-framed homes can be made to meet the current codes. What matters is how the home’s “weak points”—roofs, vents, eaves, windows, exterior walls—are designed to keep fire out.
“Protection for any home is not a singular material choice,” reads the statement. “It begins with building to current WUI code requirements, which ensures that each component of the building envelope is hardened to an appropriate level.”
The wood industry’s perspective is codified. Literally.
Hardening in theory
Wildfire building codes in California set fire-resistance standards for a home’s exterior, but they don’t dictate the materials to be used, just how well those materials withstand fire. (Washington and Oregon had similar statewide codes. Washington’s code is currently on hold until the state finishes its new wildfire hazard maps, while Oregon’s code now holds only where local governments choose to adopt it.)
This open-mindedness toward materials is also the consensus opinion among engineers who study home hardening. They have a solid reason for their position: the insides of our homes are filled with furniture, clothes and other flammable things.
“We’re trying to fortify the exterior of our houses because once the fire gets inside the house, really not much of the house has to burn for it to be a complete insurance loss,” says Erica Fischer, associate professor of civil and construction engineering at Oregon State University.
Fischer, a former practicing structural engineer who studies how different building materials hold up under earthquakes and fire, says although wood frames can add to a building’s “fuel load”— meaning it can burn along with a building’s contents—wood nonetheless has many benefits that other materials lack, including being light, which means it performs well in earthquakes.
Additionally, wood is ubiquitous in the building trades.
“This country is really good at growing timber,” says Fischer. “It’s a crop here in the Pacific Northwest … It doesn’t take extraordinary skilled labor [to work with]. The barrier to entry is very low, but also what is low is the cost.”
Besides, says Fischer, even non-wood homes need to deal with fire getting in through windows and other openings.
“And we’re going to continue to have windows,” says Fischer. “You don’t want to live in bunkers.”
Fischer’s case for wood is a strong one. But for me it raised a larger question: How have wood and alternatives held up in real fires? Turns out, it’s not an easy question to answer.
Lack of data
The most frustrating thing I encountered while researching this story was a lack of good independent data, or any data at all.
For instance, the insurance industry-backed Insurance Institute for Business & Home Safety (IBHS) does postmortem analysis of fires, tracking how hardened homes held up (or not) in conflagrations like the January 2025 Eaton and Palisades fires.
I was unable to find a postmortem analysis that tracked what homes’ frames were made of. The reality, no doubt, is that wood dominates homes construction in this country and there simply aren’t enough alternatives to bother counting.
I also was unable to find a study that isolated how much a home’s wood frame, on average, adds fuel to a house fire.
The most useful source I found was a 2025 study that calculated air pollution from burned buildings using COMBUST, a national dataset that estimates the combustible mass of U.S. buildings.
COMBUST separates a building’s materials from its contents but doesn’t separate the frame from the siding, roofing and other materials.
The emissions study, however, combined both building contents—furniture, clothes, books—and the building itself—framing, siding, roofing—into a single fuel load per building. No help there.
Additionally, while there are studies of how steel-framed and concrete homes fare in fires, most are tests run under controlled conditions, and the results, while generally favorable, are mixed.
Data about real-world performance are often anecdotal and frequently come from industry promotions.
I aired these frustrations in a phone interview with Michael Gollner, associate professor of mechanical engineering at UC Berkeley, who has studied building performance after real-world California wildfires as well as how full-sized houses burned under controlled conditions in the lab. He confirmed my suspicions.
“It’s pretty common in this field that most of the data is anecdotal and provided by the industry solution,” says Gollner. “And not to say that many of the solutions don’t have benefits, but there isn’t good data to support them.”
What there is data and research on is how well hardening has worked during actual fires.
Hardening in practice
In its final report on the Eaton and Palisades fires, IBHS found that the closer a home was to its neighbors, the more likely it was to be damaged or destroyed. No surprise there.
What was surprising was how home-hardening measures performed when houses were near and far apart.
IBHS tracked four kinds of home hardening—noncombustible siding, fire-rated roofing, double-paned windows and enclosed eaves—examining how well these held up at different distances.
At less than 10 feet from neighboring structures, houses with all four hardening measures had less than a 50% chance of going undamaged. At 10 to 20 feet apart, hardened homes had a 58% chance of going undamaged; at 20 to 30 feet, it was 68%, according to IBHS.
Go past 30 feet, however, and the advantages of hardening level off. Why? Because, as the IBHS report states, at that distance “even non-resilient components can increasingly resist the thermal exposure.”
In other words, if homes were far enough apart, hardening mattered less. Studies of other fires have concluded that how close homes are to one another is a major factor in whether they survive.
Spacing or managed retreat
So, rather than putting too much emphasis on hardening homes, should we focus on spacing them farther apart?
UCLA professor Stephanie Pincetl, founding director of the California Center for Sustainable Communities, says it’s the wrong question. The real problem is where we build.
“I think it’s time to consider managed retreat,” says Pincetl. “We should no longer be building out into flammable areas, period.”
Pincetl, who has been critical of the rush to rebuild following the LA County fires, says spacing houses farther apart runs headlong into other environmental considerations, like the need to cut back on urban sprawl. It’s also unlikely to lead to fewer fires. Quite the opposite.
As Pincetl says, the farther apart we set houses, the farther into the wildland-urban interface humans tread, and because most fires are human-caused, more people will mean more fires.
“I think the requirements for home hardening are really important … and they will take the edge off of some of the fire risk,” says Pincetl. “But I also just think that we should stop building cities out into flammable areas.”
Coin flip or half-full glass?
Pincetl isn’t alone in thinking that spacing buildings farther apart means building farther out, and that this is a bad idea.
In California, environmental groups have started using wildfire risk to block new developments in fire-prone areas. Managed retreat, however, is bound to be unpopular, maybe even political suicide.
Given this, the question becomes: how well would our current methods of home protection hold up if done perfectly, with our homes as tightly packed as they often are in the real world?
Well, it depends on whether you’re a glass-half-empty or glass-half-full kinda person.
The most revealing analysis I ran across was in a 2025 paper published in Nature Communications that used real-world, post-fire data and mixed it with computer simulations to run a series of “what if” scenarios for five California fires, including the 2018 Camp Fire.
The paper’s goal was to determine how the rate of homes lost to the five fires might have changed if hardening had been different. Spacing between homes wasn’t altered at all but instead reflected actual distances between homes.
The study also looked at defensible space.
In addition to home hardening measures, experts recommend that homes have a “defensible space” around them that has been cleared of combustible materials, including flammable plants and flammable materials touching the home, especially wood decks and fencing.
The paper ran four “what if” scenarios that went from no hardening and no defensible space to ideal hardening with ideal defensible space, in this case 30 feet. Critically, the scenarios assumed no firefighters to put out the flames.
Unsurprisingly, the do-nothing scenario created the most catastrophic results: only 20% of homes survived. But even in the ideal scenario, only 48% of homes survived.
“That’s fundamentally saying that if you have a fire, the survival [probability] of your house has the same chance as a flip of a coin,” says Michele Barbato, professor of structural engineering and structural mechanics at UC Davis, who was not involved in the study.
“No one is designing a car that will have a 50% chance of crashing on its own and saying, ‘Okay, we did the best we could do,’” says Barbato.
UC Berkeley’s Gollner, senior author of the study, has a more optimistic take.
“I don’t think we’re talking about a coin flip,” says Gollner.
The problem with Barbato’s analogy, according to Gollner, is that most of the houses in the study were older and sat in fire-prone landscapes, “the worst of the worst possible areas,” as he put it. The study also didn’t include firefighters. Add firefighters and more houses get saved.
“The big outcome [of the study] is that hardening and defensible space does matter and does make a difference,” says Gollner.
Echoing Fischer and the current engineering consensus, he said it’s important to think of houses, yards and all, as whole systems with weak spots, especially windows and doors. Keeping flames out is the point.
“If you just build a concrete bunker, even if it’s wood inside, it’s fine,” says Gollner. What brings fire into a home is its openings.
In his lab at UC Davis, Barbato and his colleagues have been experimenting with fire-resistant earthen blocks. (These have performed well in the lab but have yet to have a real-world test.) He’s also been developing an invention that he believes will help solve the problem of fire getting into homes via windows and doors.
For Barbato, the larger issue is that we’ve been writing our codes and preparing our homes for wildfires rather than for urban conflagrations, where homes fuel fires that consequently can burn far longer than a passing wildfire.
Under the circumstances, Barbato says, we need to “start building houses that don’t burn.”
“I get often the response, ‘Oh, they will look like bunkers,’” says Barbato. “In Europe we’ve been building masonry homes that are beautiful for centuries and they are more resilient to wildfires.”
Neighbors not bunkers
Fischer’s and Gollner’s bunker arguments, as dismissive as they may sound, have merit. But I think Fischer’s take in particular is wrong for a reason that only became clear as I finished my reporting.
When I spoke with Fischer, she told me about how fire can destroy concrete and deform steel, rendering the structures useless. She’s right. But consider the assumption about who benefits. It might not be the homeowner.
At the start of my reporting, Correa told me that having enough Incablock homes in a neighborhood might stop a fire from spreading. Barbato made a similar statement when we spoke. Building with wood in fire-prone landscapes, he told me, means adding “additional fuel that can damage all of the surrounding houses.”
The statements didn’t register at the time but later clicked when I was reading a study of the 2021 fire in Lytton, British Columbia.
What caught my attention in the Lytton study was a house that didn’t burn although two of its neighbors did.
There wasn’t anything special about the house left standing.
According to the study, what was unique about the unscathed house was its destroyed neighbors: both had “non-flammable stucco exterior walls” that shielded their surroundings, confining their flames to the burning houses’ themselves. These stucco walls kept fire away from the “nothing special” house next door.
The benefit of these materials, in other words, might not be that they’re impenetrable.
The benefit might be that they keep a burning house from spreading fire to its neighbors.
This, I think, is the rub when it comes to home hardening, and it complicates the call to push alternative materials into the frames of our homes: we might not be able to save our homes but we might save our neighbors’. This can happen by containing a fire from spreading, as the stucco walls did, or by building homes with noncombustible frames that simply don’t add more fuel to a fire.
And that’s a hard sales pitch. Wood is still cheaper than most alternatives, and at the end of the day, the ultimate test for these materials in the complex system that is a house will be trial by fire paid for by homeowners.
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