Wildfire Vulnerability – You’re as Safe as Your Weakest Link

In wildfires, buildings are only as resilient as their most vulnerable features. It’s often assumed that homes with metal roofs will perform better during fires than those with asphalt shingles, which are more flammable. However, analysis using the Cal Fire Damage Inspection database — which tracks all structures damaged by wildfires in California since 2012 — reveals little difference in performance between single-family homes with metal and asphalt roofs. One reason is that homes with metal roofs are more likely to have wooden walls, while those with asphalt roofs are more often built with more-fire-resistant materials. This simple example highlights the importance of considering a building’s complete set of features when assessing its wildfire resilience. Focusing on just one or two attributes can provide a misleading picture.

Caption: Assessment of the influence of roof type and wall type of wildfire vulnerability. Left plot shows average damage of buildings in wildfires with 50+ buildings with asphalt and metal roofs in the Cal Fire Damage Inspection Database (https://data.ca.gov/dataset/cal-fire-damage-inspection-dins-data). Average calculated assuming categories ‘No Damage’, ‘1-10% Affected Damage’, ’10-25% Minor Damage’, ’25-50% Major Damage’, ’50-100% Destroyed’ which are given values of 0, 5, 17.5, 37.5 and 100% loss, respectively. Right plot shows proportions of different wall siding types for locations used in the lefthand plot.