Wildfire is a normal part of nature. But that doesn’t make wildfire any less of a concern for residents of the so-called “Wildland Urban Interface”—the areas throughout our nation where human habitation encroaches on fire-prone natural terrain. As climate extremes become more prevalent, wildfire risks are increasing. In response, experts are developing strategies to make homes more resilient in the face of wildfire.

Landscape

Toughening the landscape around a house is a primary tactic. Wildland firefighters refer to this as creating “defensible space.” The idea is that fire approaching a home or development will reach an area where “fuels reduction” has occurred. As the fire reaches this zone, fire intensity will decrease and the fire may even stop approaching.

Experts define four zones around a house for graduated levels of “lean, clean, and green” treatment. The 30 feet closest to a house, “Zone 1,” should be kept clear for firefighters and equipment to operate. Plantings should be limited to low-flammability species, spaced apart, and kept low to the ground. The area should be irrigated. In “Zone 2,” plants may be spaced closer together, but should still be kept watered. In “Zone 3,” some well-spaced trees are okay, but they should be kept pruned with the lowest branches being 6 to 10 feet above the ground. “Zone 4” is the natural surrounding area. Even here, trees should be selectively pruned and highly flammable plants should be removed.

Appropriate pruning and thinning of trees and shrubs near a home helps firefighters suppress fire as the wildfire front approaches the structure. Above, a Colorado Springs firefighter successfully defends a house during the 2013 Black Forest fire, which destroyed more than 500 homes. The truck and crew worked for hours at this location, carefully rationing their limited water supply, but saving the home as the flames crept along the ground through the area.
Appropriate pruning and thinning of trees and shrubs near a home helps firefighters suppress fire as the wildfire front approaches the structure. Above, a Colorado Springs firefighter successfully defends a house during the 2013 Black Forest fire, which destroyed more than 500 homes. The truck and crew worked for hours at this location, carefully rationing their limited water supply, but saving the home as the flames crept along the ground through the area.

Walls

Even when the landscape is managed so that flames do not encroach on a building, homes are vulnerable to ignition by radiant heat exposure and by exposure to wind-blown embers. Accordingly, structures should be hardened to resist those exposures. Siding should be non-combustible (fiber-cement siding, metal siding, and stucco are good examples).

At wall bases, take care not to leave wall sheathing edges exposed to ignition from embers. Covering this exposed edge with metal flashing, concrete, or fire-resistive foam or caulking is recommended.

Windows

One common way that homes ignite in a wildfire is for radiant heat to cause glass in windows or doors to break, followed by intrusion of flame or wind-blown flying embers. Studies have shown that tempered glass is resistant to breakage from radiant heat, and that dual-pane windows are tougher than single-pane windows. Jurisdictions in the wildland-urban interface often require that the outer piece of glass in a dual-glazed window be tempered glass.

Eaves

Roof edges are a vulnerable spot in a wildfire. Burning vegetation near the house can ignite the eaves, or windblown embers may collect in a gutter, igniting debris and potentially igniting the roof sheathing or roofing. To address this concern, eaves should be constructed with noncombustible material such as fiber cement or stucco.

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In a big wildfire, strong winds may carry hot embers or even large flaming firebrands for long distances. Embers can be sucked into soffit vents or land in gutters, where accumulated pine needles or leaves may catch fire. The detail above reduces these risks; the soffit and fascia are noncombustible fiber cement, the roof is concrete tile, and metal flashing laps down into the metal gutter. The rough bottom surface of the tile allows moisture to weep out, but restricts the entry of flame and embers.
In a big wildfire, strong winds may carry hot embers or even large flaming firebrands for long distances. Embers can be sucked into soffit vents or land in gutters, where accumulated pine needles or leaves may catch fire. The detail above reduces these risks; the soffit and fascia are noncombustible fiber cement, the roof is concrete tile, and metal flashing laps down into the metal gutter. The rough bottom surface of the tile allows moisture to weep out, but restricts the entry of flame and embers.

Vents

Crawlspace vents, soffit and eave vents, or gable vents represent a risk of ignition for buildings in a wildfire. Windblown embers can be sucked into the vents and ignite framing or other construction materials in the attic. The larger the embers, the greater the risk of ignition. To guard against this risk, cover vents with ⅛-inch galvanized steel or stainless steel mesh. Manufactured vents with pre-installed metal mesh are available in the market.

Colorado Springs builder Andy Stauffer installs a screened vent in the soffit of a home near the city.
Stauffer and Sons Inc. Colorado Springs builder Andy Stauffer installs a screened vent in the soffit of a home near the city.

Roofs

Windblown embers can collect on a roof, particularly in valleys, and ignite the roofing and roof framing and sheathing. Wood-shingle or shake roofs are particularly vulnerable to ignition and should not be used in a wildland-urban interface. Instead, choose a Class A roofing material. Clay or concrete tile or slate are good choices. Most fiberglass-asphalt shingles and most metal roof assemblies are also rated as Class A.