Wildland-Urban Interface Fire Codes Are Largely Unproven — Building Codes Address the Wrong Fire Exposure

Over 46 million U.S. residential structures are at risk from wildland-urban interface (WUI) fires, but NIST research has found that "WUI fire codes and standards remain largely unproven to actually mitigate WUI fire spread and structure ignition." Current building codes reference fire test methods (ASTM E119, UL 263) designed for urban fires — flame contact and radiant heat — but NIST demonstrated that the majority of WUI structure ignitions are caused by firebrands (embers), not direct flame. The fire exposure building codes test for is fundamentally different from the fire exposure that actually destroys WUI buildings.

WUI fires destroy thousands of structures annually — the 2025 Los Angeles fires caused hundreds of billions in damages, and the problem is worsening as development pushes into fire-prone landscapes and climate change extends fire seasons. Building owners who comply with existing fire codes may still lose their structures because the codes are not based on realistic WUI fire exposure science. Insurance companies are withdrawing from WUI areas entirely because there is no reliable way to measure or certify building resilience. Traditional fire codes address individual buildings, but WUI fire is a community-level phenomenon — one burning structure generates firebrands that ignite neighbors — requiring community-scale risk assessment that no code framework provides.

NIST developed the Fire Risk Reduction in Communities Program and a proposed WUI Hazard Scale. They built specialized firebrand generators for laboratory research and conducted post-fire data collection on parcel vulnerabilities. NIST convened ISO TC92/WG14 ("Large Outdoor Fires and the Built Environment") and co-developed ISO TR/24188. However, "WUI fire science is much less developed than more mature areas of fire safety science." The physics of firebrand generation, transport over kilometer-scale distances, and ignition of building assemblies are far more complex than flame spread. There is "currently little quantifiable information that links the ember generation from wildland fuels to building assemblies testing." Community-level fire modeling requires integrating vegetation, topography, weather, and structure vulnerability at scales that exceed current computational capability. Even if NIST develops the science, adoption by the ICC's WUI Building Code and then by local jurisdictions adds years of delay.

Validated fire exposure standards based on firebrand flux rather than flame contact — essentially, testing building assemblies against the actual threat. This requires quantifying firebrand generation rates from burning vegetation and structures, and developing standardized ember exposure test methods that building materials can be certified against. A community-scale vulnerability model that accounts for structure-to-structure fire spread (the cascade effect) would enable risk-informed code requirements at the neighborhood level rather than building-by-building.

A team could build a small-scale firebrand generator (NIST has published designs) and test the ignition vulnerability of common building assembly details — attic vents, deck-to-wall connections, eave gaps — to quantify which entry points are most vulnerable. Alternatively, a team could develop a GIS-based neighborhood fire spread model using publicly available parcel data, vegetation maps, and topography, producing community-level risk maps. Relevant disciplines: fire protection engineering, materials science, GIS/geospatial analysis, mechanical engineering.