California’s WUI requirements are in the California Wildland-Urban Interface Code and apply to new buildings with permits submitted on or after July 1, 2008 in any Fire Hazard Severity Zone or designated WUI Area (§ 101.3.1; § 101.3.1.1). Chapter 5 requires ignition-resistant construction for exterior components—including roof coverings, eaves/soffits, gutters/downspouts, exterior walls, doors/windows, vents, underfloor areas, and accessory structures—supplementing the CBC/CRC (§ 501.1). A key prescriptive item is vents: openings must use OSFM-listed Wildfire Flame and Ember Resistant vents tested to ASTM E2886, with off-ridge/ridge vents protected by noncombustible, corrosion‑resistant mesh sized between 1/16 inch (1.6 mm) and 1/8 inch (3.2 mm), and with a temperature limit of 662°F (350°C) on the unexposed side (§ 504.10; § 504.10.1; § 504.10.2). Exceptions include Group U accessory structures not exceeding 120 square feet (11 m²) located at least 50 feet (15 240 mm) from an applicable building (§ 501.1). The code official may also require a project-specific fire protection plan addressing access, water supply, and defensible space compliance (§ 602.1; § 602.2; § 601.3).
Where it applies and key exemptions
- Required for “applicable buildings” in any Fire Hazard Severity Zone or WUI Fire Area; additions/remodels to buildings originally built before July 1, 2008 are exempt (§ 101.3.1).
- Group U accessory structures ≤ 120 square feet (11 m²) and agricultural Group U buildings are exempt when ≥ 50 feet (15 240 mm) from an applicable building on the same lot (§ 501.1).
- All specified distances are measured along the ground unless stated otherwise (CCR Title 14 §1270.08).
Construction features regulated
- Chapter 5 covers underfloor protection, roof coverings, eaves/soffits, gutters/downspouts, exterior walls/doors/windows, ventilation openings, appendages, and detached accessory structures (§ 501.1; Chapter 5 user notes).
- Specific prescriptive details for roof coverings, eaves/soffits, gutters/downspouts, exterior walls, doors, windows, underfloor areas, and detached accessory structures are referenced in §§ 504.2–504.11; however, those detailed material/assembly prescriptions are not included in the provided excerpts. The vent requirements above are provided in full (§ 504.10; § 504.10.1; § 504.10.2).
Site access, water supply, and defensible space
- New subdivisions and individual structures must provide fire apparatus access per the California Fire Code and CCR Title 14, and a conforming water supply per CFC § 507 and CCR Title 14 (subdivisions: § 402.1.1, § 402.1.2; individual structures: § 402.2.1, § 402.2.2).
- A fire protection plan may be required; it must show conformance with PRC 4290 (access/egress) and PRC 4291 or Gov. Code 51182 (defensible space) and identify mitigation measures (§ 602.1; § 602.2).
- “Defensible space” is defined in Chapter 6; maintenance responsibilities and specific distances are referenced but the detailed defensible-space distances are not included in the provided excerpts (§ 601.3; § 604).
Note: Appendices (e.g., home-hardening suggestions) are not mandatory unless locally adopted (§ 101.2.1).