High fire hazard Wildland Urban Interface (WUI) residences in California lack voluntary and mandated wildfire risk mitigation compliance in Home Ignition Zones

Wildfire structure losses are increasing globally and particularly in California, USA. Losses can be mitigated in part by changes to the Home Ignition Zone (HIZ), including both home hardening and defensible space. In the United States, there are local, nation-wide, and industry-based home mitigation standards that are enforced or recommended. We explore the standards implementation (California code and two voluntary standards) at 176 participating residences in three Santa Cruz Mountains and two Sierra Nevada Mountains sites. Overall most residences had little compulsory or recommended mitigations completed, and few mitigated 80% of items to meet a “harm reduction” threshold. Participants struggled with hazards that required frequent maintenance. Some hazards that, if present, were not mitigated well include woodpiles, propane tanks, trees and shrubs, roof and gutter and deck debris. We explored why some common maintenance issues occurred e.g., debris on structures. Debris on roofs and in gutters was most influenced by canopy cover, and to a lesser extent by materials. For example, smooth metal roofs shed debris better than clay tiles or asphalt shingles. Gutter debris guards lowered the debris probability in gutters, including on gutter guards. While we document much lower rates of mitigation compliance amongst residents than agencies and self-reported research, our findings are similar to others with independent inspectors. Overall, policies and research would benefit from more consistencies across programs, clarifying and/or decoupling mitigations, and standardized evaluations. Moving forward, we recommend “mitigate the need to mitigate” since most residents struggled to keep up with maintenance.