Fire researchers burn down homes to show how to save them

On a concrete pad in San Diego, firefighters dab flaming drops of fuel outside two nearly identical sheds. As the mulch around them burns, a row of fans starts to blow, simulating how a windstorm intensifies wildfires. Once the flames approach the huts, something remarkable happens: One structure is quickly consumed in a tower of flames, leaving little but ashes. The other hut emerges unscathed.

Why do some homes burn in wildfires while others do not? Researchers, insurers and government officials have been scrambling to answer this question, made urgent by a decade of deadly conflagrations: the Western fires in 2015, Paradise in 2018, Lahaina in 2023 and Los Angeles this year.

The investigations have involved sifting through the ashes of real wildfire disasters. Researchers have also blasted embers into massive wind tunnels and torched purpose-built homes in deliberate infernos like the one in San Diego.

While it can be tempting to attribute the survival of some buildings to luck, more often it’s a matter of design.

Three simple things, it turns out, confer most of the protection you need against wildfires: using fire-resistant materials for roofs and exterior siding, installing screens on vents and clearing five feet of nonflammable space around your house.

The cost to incorporate these elements in a new home is the same or less than conventional materials, according to the research group Headwaters Economics. If you’re updating your home, the price may range between $2,000 and $15,000. But some crucial upgrades – such as installing a vent screen – can cost less than $20.

We can’t stop all wildfires from igniting. But if more people took these simple steps, fire researchers say, we could prevent the massive fires that spread block to block, ravaging cities such as Los Angeles.

“We either adapt to the risk of wildfire in advance or in reconstruction,” said Dave Winnacker, a California-based former fire chief who started a company that models fire risk. “But we’re going to have to adapt to it.”

Here’s how to increase the chances that your home is among the ones left standing.

What to know about how urban fires spread

For decades, government agencies tried to protect property by preventing forest fires and extinguishing them once they started. That’s no longer a sufficient strategy in an era when tinder-dry forests, persistent droughts and climate change mean wildfires are roaring back more fiercely and frequently.

A string of unprecedented, multibillion-dollar wildfire disasters starting in 2015 prompted the insurance industry to look for underlying causes, said Faraz Hedayati, a scientist with the Insurance Institute for Business & Home Safety , an insurer-funded group that researches ways to mitigate natural disasters.

A key insight was realizing that wildfires, once they enter cities, become conflagrations fueled primarily by building materials. “These are urban fires,” Hedayati said, “not wildfires.”

Structures in the path of wildfires tend to ignite for one of two reasons. The first is direct exposure to flames, which can spread from homes or trees as far as 30 or even 100 feet away. The second is airborne embers, or firebrands. These fly miles ahead of the fire’s front, accumulating against flammable walls, roofs and other structures, and then setting them ablaze. Windstorms often further fan the flames, creating “fast fires” that can grow several football fields a minute.

What we can learn from crash-test homes

For the past year, IBHS officials have been touring the country to set buildings on fire. The simulations are pretty convincing in showing how homes built to its “Wildfire Prepared Home” standards could survive disasters like the Los Angeles fires.

During the San Diego demonstration in May, a conventionally built hut appeared to melt in the heat. First, the bushes around it were consumed in flames. The gutters and vinyl siding drooped. A window fell to the ground, welcoming flames inside. Everything combustible was soon in flames.

An identical-looking structure – featuring fire-resistant siding, vent screens and five feet of noncombustible space around its foundation – was virtually untouched.

Once densely packed structures ignite, it’s difficult, if not impossible, to prevent the spread to directly adjacent buildings. Broad adoption of these measures could prevent that.

“It’s as close to 100 % as we can get in this space,” Winnacker said. “It’s extraordinarily effective.”

Install screens on your vents

Metal screens on vents prevent embers from entering homes and igniting them from the inside. Entrance vents on roofs, plumbing, attics, basements and elsewhere should be covered with a mesh of ⅛ inches or finer. These are typically installed with screws and fire-resistant caulk or sealant. “When I was in L.A. (after the recent fires), I didn’t see a single proper installation of screens,” Hedayati said. It’s a cheap fix: “You can take care of an entire building for less than $100,” he said. Incorporating fire-rated vents can also help keep out embers and flames.

Choose fire-resistant materials

Home exteriors should integrate noncombustible materials. That means going with a Class-A roof – those include asphalt, clay tile, metal or concrete slate. For the exterior walls, it’s important for the bottom six inches to be made from materials such as fiber cement, stucco, stone or brick. Avoid gutters and downspouts in materials that are prone to burn. Dual-pane windows can also act as fire barriers.

The appearance of fire-safe materials can be virtually indistinguishable from their flammable counterparts and cost the same or less, according to Headwaters Economics. In many parts of the country, building codes have been updated to make some of these materials mandatory (almost all homes IBHS surveyed in Los Angeles already had Class-A roofs installed).

Clear at least 5 feet of space

A “zero zone” around a home can act as a noncombustible moat. The IBHS demonstrations, for example, use a concrete pad (or hardscape such as gravel, pavers, river rocks and stepping stones) with metal patio furniture and no vegetation or flammable plantings at the base of the home.

For added protection, IBHS also recommends removing things that could burn within 30 feet of a home: relocating propane tanks or piles of wood, spacing out shrubs and trees, pruning low-hanging tree branches, keeping grass cut to less than four inches (or 18 inches in areas needing erosion control) and removing dead or dying vegetation.

Flammable materials such as firewood, cars, fuel tanks etc. near the house during an intense firestorm mean “there’s a zero percent chance of survival for structures,” Hedayati said. “You’re holding a giant blowtorch on your home. That’s the reality.” Removing them, he estimated, cuts the risk of loss by more than 50%. Architects are now designing beautiful fire-safe homes and landscapes to overcome aesthetic objections (I’ll cover this in a future column).

A few caveats to guard your home against wildfires

You can’t cherry-pick a few measures. “It’s not just one feature,” Hedayati said. “It’s all three working in combination.”

Upgrading only your home isn’t enough. Roughly one-third of structures in a grouping need to take these measures before you begin to see significant fire reduction benefits. IBHS recommends at least 90 % of homes on a block or within a “cluster” (structures separated by roads and parks) adopt the measures for maximum protection. “This level provides a balance between practical feasibility and meaningful risk reduction,” Hedayati said.

But it’s likely to pay off. IBHS’s wildfire prepared home standard allows homeowners to get certified and (eventually) receive discounts on their insurance in California, a model likely to be adopted by other states.