Wildfire Roofing

Wildfire roofing refers to the choice of roof coverings and details that help a building survive a wildfire (called a bushfire in Australia). The roof is a large, upward-facing surface that collects wind-blown embers, and research and post-fire surveys consistently identify embers as a major cause of home ignition.

How roofs ignite

• Embers (firebrands). Wind can carry burning fragments well over a kilometre ahead of a fire front. Embers that land in gutters, valleys, roof debris or gaps under tiles can ignite leaves and combustible materials. Embers that enter vents can ignite the attic.
• Radiant heat. Nearby burning vegetation or buildings can heat roof edges and openings to ignition.
• Direct flame contact. Flames from vegetation, fences or decks close to the house can reach eaves.

The Insurance Institute for Business & Home Safety (IBHS) notes that no single hardening measure fully protects a building and recommends a system-based approach.

Roof coverings

Fire classifications such as Class A under ASTM E108 or UL 790 in North America indicate how a covering performs against external fire. Materials commonly available with Class A ratings include asphalt shingles, metal, clay and concrete tile, and slate, sometimes with a specific underlayment. Untreated wood shakes perform poorly and can themselves generate embers; many fire-prone jurisdictions restrict them.

Details that matter

• Gutters and valleys: keep free of leaves and needles; non-combustible gutter guards can help.
• Gaps at ridges and eaves: under barrel tiles and profiled panels, bird stops or closures keep embers and debris out.
• Vents: eave, gable and roof vents should have fine non-combustible mesh or ember-resistant vent designs.
• Eaves and soffits: enclosed, non-combustible soffits resist ember entry better than open rafter tails.
• Roof-to-wall junctions and skylights: need non-combustible flashing and tempered or rated glazing.

Surroundings

Guidance in the United States describes a Home Ignition Zone, with the first 1.5 m (5 ft) around the building kept free of combustibles. IBHS experiments found that even well-watered plants within that zone can increase heat exposure. Trees should be pruned back about 3 m (10 ft) from roofs.

Regional codes

California's building code has dedicated wildland-urban interface requirements, the International Wildland-Urban Interface Code is used in other US jurisdictions, and Australia uses AS 3959 with Bushfire Attack Levels. In the US, the wildland-urban interface was the fastest-growing land-use type between 1990 and 2010, increasing the number of homes exposed.