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Fire Resistant Roofing

The roof is the most vulnerable part of your home in a wildfire. Its large surface catches embers the way it catches rain, and an unrated wood shake roof can turn a single ember into a total loss. A Class A roof, kept clear of debris, is the foundation of a hardened home.

Roof Fire Ratings

Roof coverings are fire-rated Class A, B, or C, with Class A providing the highest protection. The rating comes from a standard test (ASTM E108) that evaluates flame spread across the covering, fire penetration into the attic, and the ember-generation potential of the covering itself. Class A roofs are widely available and affordable: composition shingle, metal, and tile all qualify. At minimum, any unrated roof, such as untreated wood shakes, should be replaced with a rated roof.

What California requires: new construction in designated fire hazard severity zones must meet the wildfire building standards in California Building Code Chapter 7A, which requires a fire-rated roof, Class A in Very High zones. If you are re-roofing an older home in San Mateo County, go straight to Class A. Your local building and fire departments can confirm the requirements for your address.

Stand-Alone vs. Assembly Ratings

A burning Class A test brand positioned on a roof covering during an ASTM E108 fire test

A covering can earn Class A on its own (stand-alone) or in combination with an underlying material (Class A by assembly). Most noncombustible coverings, such as tile and most metals, are stand-alone Class A. Aluminum is the exception: its low melting point means it must be tested and requires an additional underlying material to reach Class A by assembly.

Wood shakes pressure-impregnated with fire retardant can achieve a Class A assembly rating. In California they must also pass a natural weathering test and be registered with the Office of the State Fire Marshal Building Materials Listing Program, and some communities do not allow them at all.

If you use an assembly-rated covering, follow the installation instructions exactly and use all specified materials. Substitutions and shortcuts reduce the fire performance the rating is based on.

A Class A Roof Is Not Enough by Itself

Dead leaves and needles accumulated at a roof-to-wall intersection, where ember ignition would expose the adjacent siding to flames

Complex roofs, those with many horizontal-to-vertical intersections such as dormers and roof-to-wall junctions, collect windblown debris and embers at exactly the points where different materials meet. If debris ignites at a roof-to-wall intersection, the flames attack the siding, sheathing, or a window, not the Class A covering. On a complex roof, the fire resistance of those adjacent components determines the roof's real vulnerability. Two habits matter regardless of roof type: keep the roof surface and its intersections free of debris, and keep tree branches from overhanging the roof.

Roofing profiles with openings between the covering and the sheathing, such as barrel tile at the eaves and ridge, need those gaps plugged (bird stops) so embers cannot lodge in them.

Skylights

Skylights are small but real entry points. Flat skylights use tempered glass; domed skylights have a plastic outer shell that can deform under radiant heat. If your skylight opens, close it when fire threatens. Keep debris cleared from around skylights, especially flat units on low-slope roofs, and remove overhanging branches that could fall and break them.

Roof Edges and Rain Gutters

Debris-filled gutters are an ember trap: ignited gutter debris puts direct flame on the roof edge, the fascia, and any exposed sheathing. Metal angle flashing at the roof edge substantially reduces this exposure. The gutter's material matters less than its condition. A metal gutter holds the burning debris in place against the roof edge; a vinyl gutter melts and drops the burning debris to the ground, where it can ignite groundcover or siding instead.

  • Clean gutters before fire season and as needed through it. Debris in the gutter is the problem; remove it and the hazard largely goes away.
  • Gutter covers (screens, solid covers, or foam inserts) can reduce accumulation, but none is maintenance-free, and debris tends to collect on the roof behind them. Inspect regularly.
  • A useful pre-evacuation task if time allows: plug the downspouts and fill the gutters with water.
  • Keep gutters and downspouts for moisture management; the answer to gutter fires is maintenance, not removal.

Adapted from Quarles et al., Home Survival in Wildfire-Prone Areas: Building Materials and Design Considerations (UC ANR Publication 8393, PDF). Photos: Stephen L. Quarles. For current re-roofing guidance, see CAL FIRE: Hardening Your Home and Fire Safe Marin: Harden Your Home.