This story was originally published in Builder.
U.S.-based wildfires caused more property damage and loss of life than any other natural catastrophe in 2018, says Roy Wright, CEO and president of the Insurance Institute for Business & Home Safety (IBHS).
For instance, California’s Camp and Woolsey wildfires are estimated to have caused between $15 billion and $19 billion in damage, but wildfires were also rampant in 11 other western states, each of which had at least one wildfire that exceeded 50,000 acres last year.
Researchers at IBHS have been working for years to determine ways to combat the devastation caused by these fires. A recent demonstration looked into what causes homes to ignite during a wildfire. Through research and real-life demonstrations, the organization found that roughly 90% of homes and buildings damaged or destroyed in a wildfire were first ignited by embers or other fires set by embers, and not the actual wildfire front.
During a wildfire, these embers, or fire brands, can fly for miles and start a new fire when they land, says Daniel Gorham, research engineer at IBHS. If they get inside a home through vents or an open window or land on dead landscaping, dry wood, or common home building materials, houses become extremely at risk.
“These wildfires are becoming far more severe,” says Wright. “Yet there are practical steps that can be taken by individual property owners, community planners, and state and federal leaders to reduce our collective risk from wildfire and make our neighborhoods safer and more resilient.”
For the test, IBHS engineers and researchers designed and built a full-size duplex, a 30-foot by 20-foot building with each side of structure treated with different building materials. One side was deemed at high risk for fire and built with cedar-shingle siding, vinyl gutters, single-pane windows, and bark mulch around the foundation. The other side was designed to be fire-resistant and built with fiber-cement siding, metal gutters, multi-pane windows, and gravel.
The completed structure was placed on a turn table, similar to ones used in the railroad industry, for added mobility. This allowed researchers to rotate the building 360 degrees if needed. The duplex was then moved into the IBHS test chamber with more than 100 fans and ember generators to simulate an active wildfire and winds in front of the two attached homes.
Within five minutes of embers impacting the demo home, the bark mulch on the non-fire-resistant side ignited. The flame then spread to the siding and up the exterior wall to the eave area. Local firefighters were on scene to suppress the fire once it got to the roof, in order to repeat the experiment multiple times.
“Wood mulch is a pretty common landscaping material and I understand the use of it, but the problem is it is combustible,” says Gorham. “It has lots of little crevices for those fire embers to land in, sit there, and smolder.”
Gravel mulch on the other side, along with its other fire-resistant features, prevented the embers from igniting a flame during the test time, even with the non-fire-resistant side ablaze.
Protecting the Property
The experiment showed that the key to improving wildfire resistance for homes and other buildings is twofold: a series of zones around the home and the fire-resistant building materials used to construct it. IBHS researchers recommend to create a complete noncombustible space close to the home and be aware of the defensible space, observed in three zones, from 5 to 100 feet from the house.
Zone one is the 5-foot space around the complete perimeter of the home’s exterior walls, including underneath attachments like decks. This zone should be completely noncombustible and include nothing that could potentially ignite a fire, including dead leaves, twigs, bushes, or plants. Materials such as gravel, brick, or concrete are suggested instead.
The next zone is 5 to 30 feet away from the home and zone three is 30 feet and beyond. While these two zones aren’t recommended to be completely noncombustible, homeowners should be vigilant of the nearby vegetation and schedule routine landscaping maintenance.
In addition to the defensible space, builders should carefully consider their product choices and only use roofing, siding, window, and door products that carry a Class A fire-rating. Other recommendations include specing multi-pane windows with tempered glass, maintaining 6-inch ground-to-siding clearance, using 1/8-inch mesh to cover vents, and boxing in open eaves.
Builders should also consider using deck boards that comply with new construction requirements in wildfire-prone areas and building fences and gates with noncombustible materials, such as metal.
Researchers say that these steps don’t have to cost more money. A 2018 report by Montana-based Headwater Economics and IBHS determined the cost of constructing a wildfire-resistant home is about the same and sometimes less than building a typical single-family home.
In the future, the team hopes to discover whether the quantity of embers or the overall surface area of the embers affects ignition and if there are additional ways to prevent ember entry into buildings.
“This demonstration put all the pieces together,” says Gorham. “It’s really a powerful image to show a single house with the side-by-side and see how one was affected and one was not.”
This story was originally published in Builder.