Vulnerability of Vents to Wind-Blown Embers

Wind-blown embers are the principal cause of building ignitions during wildfires. Although the role of embers (also called brands or firebrands) has long been recognized, the ability to evaluate ember exposure in a controlled laboratory setting is relatively new.

Research

Ember Entry: Vents

Since 2010, the Insurance Institute for Business & Home Safety (IBHS) has conducted systematic research to understand how wind-driven embers enter buildings through attic vents—one of the most vulnerable points in a structure.

This work, led by Dr. Steve Quarles, established the foundation for evaluating common vent designs and identifying pathways for ember intrusion.

To build on these findings, IBHS conducted a second, more comprehensive series of experiments in 2013–2014. The objective of this study was to clarify the relative importance of vent style, type, and location on the entry of wind-blown embers. At the time, three vents approved by the California Office of the State Fire Marshal (OFSM) were included in the experimental design to assess their performance.

Researchers tested both inlet vents (open-eave and soffited-eave configurations) and outlet vents (gable, ridge, and off-ridge vents) under varying wind speeds and directions. Using IBHS’s rotating test building, the team precisely controlled wind angle and intensity, enabling detailed evaluation of how airflow and vent placement influence ember penetration.

Through video documentation and instrumented measurements, the study demonstrated that vent type, configuration, and orientation significantly affect ember entry. These results provide critical scientific support for improving vent standards and guiding mitigation strategies aimed at reducing ember ignition in attic spaces.

Citation

Quarles, Stephen L. “Vulnerability of Vents to Wind-Blown Embers.” Insurance Institute for Business & Home Safety, 2017. https://doi.org/10.82346/F4F5-SH90.