Why do some houses survive a wildfire?

There is some hope among the smouldering ruins of many parts of Los Angeles. Entire neighbourhoods were ravaged by the recent wildfires but, among the devastation, the odd house stands whole, completely untouched by the flames that burned those around it to the ground.

Houses like these “are heralded as miracles”, said National Geographic, and images of their solitary survival have been shared thousands of times by astonished social media users. Although luck may have played a part, what saved these houses from destruction was almost certainly a combination of fire prevention measures their owners had carefully put in place.

‘Hardened’ homes

It all starts with “home-hardening”. Building – or retrofitting – a house with specific fire-resistant materials is “absolutely critical”, Daniel Berlant, a Californian fire officer told the Los Angeles Times. Ditching wooden decks and shingle roofs and installing cement stucco walls, a metal roof and gutters, tempered window glass and mesh screening on chimneys, eaves and vents can mean a “double-digit increase” in a house’s chances of surviving a fire.

However “hardened” your home is, though, constant vigilance is required. That means clearing debris off the roof and leaves out of gutters, plugging gaps in rafters, checking the holes in mesh screening aren’t big enough to let flying embers through, and never leaving cardboard packaging or recycling piling up by your door. There are “50 ways a fire can burn your house”, Californian architect Greg Faulkner told The Associated Press. If you “eliminate” three-quarters of them, “that’s not luck, that’s increasing your odds”.

‘Defensible spaces’

What is – or isn’t – around the house matters, too. Studies show that flying embers from smouldering material are responsible for “up to 90% of structure loss” in wildfires, said National Geographic. Creating a sterile zone around a property – clearing vegetation, swapping wooden fencing for solid concrete perimeter walls – turns it into a “defensible space”, said the LA Times, where stray embers are much less likely to take hold. Local fire prevention laws in LA already require homeowners to cut grass and brush within 200 feet of a house, or 10 feet of a road or combustible fence, as well as trimming overhanging trees and spacing out bushes, to prevent them acting “like a highway for flames”, said NPR.

But proposals for stricter rules, including limiting greenery on windowsills, have so far met with strong public resistance. And there’s the problem: the defensible space around your house can only do so much; you need all your neighbours to have one, too. “Community immunity. It’s like a chain – the weakest link,” Pacific Palisades resident Steve Yusi told the LA Times, after witnessing burning debris “spew red-hot embers” on to his neighbours’ houses in Pacific Palisades.

But sometimes all the preventative measures in the world aren’t enough. Yusi spent “$75,000 on a fire-suppression system” for his canyon-edge house, “including a 2,500-gallon sprinkler system to soak the property and humidify the air for an hour”. He felt confident, even as his house was “exposed to flames racing uphill”, fanned by powerful winds. And? “It burned down anyway.”