How a home is built changes how well it resists embers and flame. California's rating regulation, 10 CCR §2644.9, ties these features and community efforts directly to insurance rates. This is how mitigation can lower insurance cost.
If an insurer's rates reflect wildfire risk, its rating plan must reflect both:
Community-level designations, such as a Firewise USA site in good standing.
Property-level mitigation efforts, such as clearing combustible materials within 5 feet of the building and hardening the building.
Building hardening measures listed in the regulation:
A Class-A fire rated roof.
Enclosed eaves. Open eaves with exposed rafter tails do not qualify.
Multipane windows or functional shutters.
At least six inches of noncombustible vertical clearance at the bottom of the exterior.
Optional factors: fuel, slope, access, aspect, wind and structural characteristics. An insurer may use them if it demonstrates they are substantially related to the risk of wildfire loss and do not produce excessive, inadequate or unfairly discriminatory rates. The regulation does not require a Wildfire Risk Model, and the mitigation factors apply either way.