Building codes & construction
WUI / Fire Hazard Severity Zone
CAL FIRE-mapped fire hazard severity zones (moderate to very high) where hardened, ignition-resistant construction and defensible space are required.
Definition
Fire Hazard Severity Zones are CAL FIRE's mapped ratings — moderate, high and very high — of wildfire hazard across both state responsibility areas and city and county (local responsibility) land; the wildland-urban interface, or WUI, is the development edge those maps formalize. Zone status is a code trigger: mapped parcels carry ignition-resistant construction requirements and 100-foot defensible-space maintenance. From the 2025 cycle the construction rules sit in the consolidated California Wildland-Urban Interface Code (Title 24, Part 7); CBC Chapter 7A and CRC Section R337, which held them before, now hold only notes pointing to Part 7. Recent map updates expanded the designated zones substantially.
Why it matters in an underwrite
Zone status changes both the cost side and the insurability of a deal: hardened-envelope requirements add real cost per building, and property and builder's-risk insurance in high and very high zones has become expensive enough to break underwrites on its own. Check the current CAL FIRE map and the local adoption before the LOI — the maps have been redrawn recently, and a parcel's zone today may not match the listing broker's memory.
Sources & related guides
See also
See the term in the law itself
Read the controlling text in the Code Library, or ask the AI how it applies to your project.
Last reviewed 2026-10-19. General information, not legal advice.