Greg Keeler, the technical services leader at Owens Corning and a former firefighter, spoke to Tanya Martins, the online editor of The Construction Specifier, about wildfire-resistant roofing and structural fire mitigation strategies.
Leveraging his experience as a firefighter, Keeler described the common vulnerabilities in roofing materials that lead to home ignition during wildfires. The most important one is penetrations of the roof, either in the soffit or the field of the roof, which can be a common source of ignition of the attic space during a wildfire.
Asphalt shingles provide a well-sealed roof surface and offer Class A fire resistance to the roof system. Thinner metals—while they do not allow particles to enter the deck—are much more vulnerable to fire because of their low melting point. Aluminum would be the primary roof covering which is a factor.
“Depending on the profile of the tile, some of them have more air space under them than others, and in fact, the California code is now addressing the vulnerability of that airspace by requiring a roof underlayment or covering under the tile that provides a Class A or ember-resistant system, because the embers can get in underneath the tile and if you do not have a good fire retardant layer there, it can cause problems,” says Keeler.
Beyond materials, some structural or design modifications can be implemented to improve the roofs’ fire resistance. The answer is switching to unvented attics, which do not have any ventilation openings. However, it is important to remain cautious about requiring ventilation because removing moisture from that space is critical.
Rebuilding for resilience
Some lessons from past wildfires can guide how the industry approaches rebuilding entire communities in fire-prone areas—the biggest one is the defensible space around the building.
“If you can prevent the fire from getting close to the building, then you know you have solved about 90 percent of the problem. There are always going to be situations where there are things flying through the air, and while you don’t have flame impingement, you still have burning brands flying through the air,” adds Keeler. “Fortifying the roof and the walls, windows, and doors against those flying brands and ember impingement, if it gets to that, is going to be the key, but the defensible space around the building prevents most of that from happening in the first place.”
“The number one thing that I would say in my discussions with the experts in the wildland-urban interface (WUI) research is that roofs, while they can be a problem, they are not the biggest problem by far. Wall claddings and windows seem to be the highest vulnerabilities, especially combustible material around the base of the building when it catches fire.”
Read Greg Keeler’s recent article on specifying fire-resistant roofs.
