During the recent Mountain fire in Ventura County, impacted neighborhoods saw random destruction. Some homes were nothing but ash and rubble, not more than a few hundred feet away, others stood seemingly unscathed.
The cause of the random ruin, the most destructive force in wildfires: embers.
Heat propels burning embers upward as wildfires scorch flammable vegetation, and then strong winds can carry them for miles. When the embers land, they can ignite new fires that quickly devour homes.
As development continues to push the boundary of the wildland-urban interface, experts are debating if homeowners can really control whether their homes survive a wildfire.
Effectiveness of Home Hardening
“It’s neither” pure chance which homes burn nor entirely determined by home hardening measures, research ecologist Alexandra Syphard told the Los Angeles Times. It’s somewhere in the middle.
In a 2019 study, Syphard attempted to quantify the degree to which home hardening measures protected homes against wildfires. Her research with Jon Keeley analyzed more than 40,000 structures in California that faced wildfires from 2013 to 2018, including the devastating Camp and Woolsey fires.
Some of the key findings include:
1. Structural Characteristics as Critical Factors
- Structural features had a more significant impact on home survival than defensible space. Enclosed eaves, vent screens, and multi-pane windows were identified as the most crucial for preventing destruction.
- Enclosed eaves reduced the chance of ember penetration.
- Fire-resistant exterior sidings and composite decking materials provided added structural protection in the Bay Area region.
2. Limited Role of Defensible Space
- Defensible space distance explained little about structure survival. Structures with larger defensible spaces (>30m) were still vulnerable to destructive wildfires, often due to traveling embers.
3. Importance of Defensive Actions
- Firefighting actions played a vital role in structure survival. In Southern California, homes protected by a fire department were 19% less likely to burn — 31% if a civilian helped defend it as well.
The findings suggest that while homeowner-level mitigation helps structure survival, other strategies need to be considered to reduce structure loss.
“If you assume that all home modifications are effective, you’re creating a false sense of security,” Syphard told the LA Times. “Other studies I’ve done have found that the most important factor that explains why a structure is destroyed in a fire is the location of the house.”
