Journal Article Investigates the Role of Residential Siding Materials on the Spread of Exterior Fires

The peer-reviewed journal article “Residential Exterior Wall Reaction to Post-Flashover Compartment Fires” has been published in Fire and Materials Journal. A part of the Heat Transfer from Structure Fires project, this research investigates the resilience of different residential siding materials on the spread of exterior fires. The article is co-authored by research engineers Daniel Gorham and Joseph Willi, and research director Gavin Horn, from the Fire Safety Research Institute (FSRI), part of UL Research Institutes.

Structure-to-Structure Fire Spread

The spread of exterior fires across buildings can cause catastrophic loss of life and property, in both wildland urban interface (WUI) fire and conflagrations. Exterior walls, windows, doors, and roofing materials all play a role in this spread and damage, with exterior walls  often constituting the largest surface area and potentially dictating whether or not a structure will burn. During FSRI’s analysis of the Maui wildfires, and now as researchers are on the ground in California, this impact has been seen firsthand. Considering this risk, it is important to understand which types of exterior walls  best protect against this spread, particularly as rebuilding decisions are made.

Testing Fire Exposure Behavior of Wall Assemblies

This research studied three different exterior wall assemblies: plywood siding panels (T1-11), fiber cement board siding, and exterior insulation finishing systems (EIFS), which is a product combining foam insulation with an exterior stucco finish. T1-11 and EIFS are considered combustible siding materials, while fiber cement is noncombustible, but had a combustible sheathing layer behind the siding. The experimental setup consisted of two components: one side was the source compartment where the fire was ignited and allowed to transition to flashover, the other side was the target façade wall assembly with heat flux gauges. To represent common separation distances between buildings in high density areas, the wall assemblies were tested at 10 feet from the source. Depending on the behavior of the siding assembly at that distance, they were then tested at 6 ft or 14 ft. Researchers measured heat flux to the wall and several components of the reaction each assembly had to fire exposure, including off-gassing, discoloration, and wall ignition.

Impact on Building Construction Materials

Key results from this experiment include:

• The wall assemblies reacted to the fire exposure in two ways: (1) flame spread across the surface of the wall and spreading to other components (vents, windows, doors), and (2) fire penetration through the assembly.
• Noncombustible siding (fiber cement) withstood higher heat flux and required closer proximity to the source fire to ignite (six feet).
• The wall assemblies consisting of foam insulation with a stucco exterior are popular for energy efficiency, but can enable fire spread by separating and melting to burn in a pool at the base of the wall.
• Comparing the results to the companion window assembly studies, exterior wall assembly failure could happen before or after window failure, depending on the window construction. This indicates that both are important factors in protecting structures.

The results from this study further the understanding of residential wall assemblies and their role in building-to-building fire spread. This work can be applied to update building codes and construction decisions to minimize loss of life and property in WUI and structure fire situations.

“Exterior walls make up a large portion of residential buildings and present a pathway for building-to-building for spread. For severe exterior fire exposure, like those that are common during WUI and conflagration fires, these walls need to resist both flame propagation and fire penetration to reduce the potential for building-to-building fire spread.”
— Daniel Gorham, research engineer, FSRI

Read the Journal Article 

About the Fire and Materials Journal

Fire and Materials is the leading journal at the interface of fire safety and materials science. The publication covers all aspects of the fire properties of materials and their applications, including polymers, metals, ceramics, and natural products such as wood and cellulosics. Papers on all areas of fire safety science and engineering are welcomed, including those on passive and active fire prevention, modeling, fire retardant chemicals, human behaviour and wildland and large fires.