Exclusive: Strategies for fireproofing energy-efficient buildings

February 19, 2024

UL Solutions experts unveil fire safety strategies for energy-efficient buildings

In an ambitious venture where fire safety meets energy efficiency, UL Solutions, the International Association of Fire Fighters (IAFF), and the U.S. Department of Energy (DOE) have joined forces. This collaboration addresses a pressing concern: the fire safety standards of energy-efficient technologies in residential properties, especially the risk of rapid fire spread through exterior walls, which are not currently subject to specific testing for this hazard.

In the collaborative project at UL Solutions, focused on enhancing fire safety in energy-efficient residential constructions, three professionals played pivotal roles. Kelly Opert, as the project manager, was instrumental in leading Initiative 1, with her responsibilities including the development of the test plan, overseeing laboratory testing, and authoring the final report.

Sean DeCrane served as a crucial liaison across both initiatives, bridging the gap between UL Solutions, PNNL, IAFF, and other stakeholders, ensuring alignment of project objectives with diverse interests and expertise. Concurrently, Dwayne Sloan significantly contributed to the test plan development and participated in advisory discussions for Initiative 1, while also serving as a technical reviewer and spearheading efforts at ASTM to establish a new standardized test method, a fundamental aspect of this project.

This project, supported by a three-year DOE grant to the IAFF, delves into two critical areas: the fire performance of energy-efficient exterior walls and the development of firefighting tactics for residential properties with energy storage systems. Building on previous research by Pacific Northwest National Laboratories, this initiative aims to enhance the adaptability of residential energy-efficient wall solutions by focusing on their fire performance.

In our exclusive interview, FSJA spoke to Opert, DeCrane, and Sloan, shedding light on their individual contributions and the collective effort that is steering this groundbreaking project towards enhancing fire safety in the realm of energy-efficient residential construction.

What was the main impetus behind the initiative to evaluate the fire safety of energy-efficient technologies in residential properties?

The DOE has supported the adoption of residential energy efficient technologies through research, education, and building code revisions for decades.  They have made great strides in improving the energy efficiency of new construction with their Building Energy Codes Program.  However, there was a limited understanding of how to approach best retrofitting existing structures with outdated or inadequate energy performance. According to PNNL, “approximately 68% of residential building stock in the country…have significant air leakage and inadequate insulation.”  This was the impetus behind the PNNL research and eventually led to our opportunity to study the fire performance of these retrofit energy-efficient assemblies.

While this was ongoing, UL FSRI had completed their report “Study of Residential Attic Fire Mitigation Tactics and Exterior Fire Spread Hazards on Fire Fighter Safety,” which included fire testing of various exterior residential wall assemblies.  The study showed that some products that improve energy efficiency contributed to inadequate fire performance.  Based largely on these findings, there were discussions at building code hearings over the need for a standardized test method to evaluate the exterior vertical flame spread of curtain wall construction. As a result, an ASTM standards technical committee initiated work to establish a fire propagation test method for residential structures and drafted a test method. 

The draft method provided a means to evaluate the fire performance of some of the residential retrofit solutionstheir. Testing the different wall assemblies enabled validation and further development of the test method.

How was the evaluation test program designed? What were its key components?

The test plan was designed by a technical panel of industry experts and informed by the PNNL reports, FSRI report, and some exploratory research UL Solutions had conducted.  PNNL assessed 15 different wall assemblies.  The baseline wall design used in PNNL research was used as the base wall for our testing.  The baseline wall “A” was designed to represent older homes without insulation and those most needing energy efficiency upgrades. With input from the technical panel, we removed solutions that had low adoptability or included materials that were not currently available on the market. Because the research focused on the exterior flame propagation, the variations of insulation in the wall cavity were not included.  Wall assemblies with exterior layers similar to the ones tested by UL FSRI were also removed from the test plan. While siding was discussed as not considerably impacting energy performance, it does impact fire performance. Ultimately, three siding materials (vinyl, engineered wood, and fiber cement) and five wall assemblies (identified as A, D, E, L, & O in the PNNL report) were chosen and used in the testing. 

Could you provide us with some insights into the various exterior wall systems that were researched during the test program?

PNNL did an extensive literature review “to identify materials, applications, and technologies that will advance envelope retrofits and provide thermal and moisture durability for existing building stock.”  In this review, they identified historic and current building practices and materials, identified currently used energy-efficient products and experimental solutions (such as aerogel insulation, phase change materials, and vacuum insulated panels), and regional environmental challenges. The key factors identified by PNNL as most influential to technology choice were physical built characteristics, climate zone, cost, material availability, and contractor expertise.  With the literature review finding and input from their technical panel, 15 wall assemblies were selected, tested, and studied to determine energy efficiency and adoptability. 

The key features of the wall assemblies chosen for our study were the following:

  • Wall “A” was the baseline representing older homes.  This wall was chosen to validate the test method fire size and demonstrate the impact of different siding materials. 
  • Wall “D” included expanded polystyrene (EPS) panels containing drainage channels and structs for securing to the wall assembly.  From a fire performance perspective, increased ventilation can provide more oxygen to the fire and increased burning.
  • Wall “E” included applying a continuous layer of extruded polystyrene (XPS) secured to the wall with furring strips with XPS infill between the strips.  The focus of this wall assembly was for the potential of the foam insulation to burn out creating a cavity for fire spread.
  • Wall “L” included applying a continuous layer of foil-faced polyisocyanurate secured with furring strips. In this wall, the flue space created by the furring strips was of interest as a possible means for fire spread.
  • Wall “O” similarly included applying a continuous layer of fiberglass board secured with furring strips.  This wall was selected to understand the potential for fire spread up the flue spaces between furring strips with non-combustible insulation.

In what ways do these innovative exterior wall systems enhance the insulative performance of energy-efficient solutions?

Each of the walls selected for our testing used exterior application of insulation over varying existing wall layers to improve energy efficiency.  In the PNNL report, they also examined different interior wall insulation; in one case, they applied foam insulation board to the interior sides of the studs.  Since exterior fire spread was the focus of this work, exterior alterations were considered the priority for study.

What were some of the most notable findings during the test program?

The variety of wall assemblies tested provided a good range of fire behavior to assess the adequacy of the test method and identify potential hazards of innovative, energy-efficient, retrofit solutions.  Results ranged from no flame attachment to fire spread reaching the top of the 16 ft (4.8 m) test wall in under 3 minutes. Peak heat release rates ranged from under 200 kW to 6 MW at test termination, and in one test, heat fluxes were above 20 kW/m2 at 8 ft (2.4 m) from the center of the wall assembly. 

The range of data validated the test method’s ability to differentiate fire performance across different wall assemblies.  The base wall prevented burn-through of the sheathing, that was observed in earlier test method iterations. The wall size was sufficient to observe the vertical and lateral flame spread behavior. The 20-minute long, 75 kW fire exposure resulted in a wide range of fire propagation rates and sizes. 

Several findings were noted regarding the fire performance of the innovative technologies.  The layering of the materials on the sheathing can substantially impact the fire performance of the wall assembly.  In one test with vinyl siding on asphalt paper, the fire reached the top of the wall sample in about 3 minutes, and in another with vinyl siding over furring strips and mineral wool board, the flame never attached to the wall.  In one test, fiber cement siding was used to cover EPS panels.  No flame attachment was noted. 

However, when some panels were removed, and the exposure fire was reignited, the fire burned into the wall consuming the panels behind the siding.  The range of fire performance is good for test method validation, but the extremes of the data should be considered.  The largest peak heat release rate was 6 MW, 30 times the size of the smallest, 200 kW. 

What challenges or unexpected outcomes came up during the test program?

The intensity of some of the fires was unexpected both in terms of the fire size and speed of propagation up the walls.  The concern over exterior fires quickly spreading up walls and into attic spaces was known; however, this work demonstrated how some attempts to gain energy-efficient designs could possibly spread fires so fast that first responders would not have an opportunity to address the fire prior to serious spread throughout the structure. In addition, existing minimum building and structure separation distances are determined based on the fire performance of common building materials and construction.  With the introduction of innovative materials and construction, there is the potential to create more hazardous fires than what building codes assumed.  This is an area for potential future research.

What impact do you anticipate this standardized testing method will have on the future of energy-efficient technologies in residential buildings?

The new draft ASTM fire propagation test method was revised based on the findings of this study and will likely continue to evolve through the ASTM proposal and balloting process. The research work using the fundamental draft enabled the creation of a base wall to which materials could be applied. The testing plan also helped identify an initiating fire size and test sample size that allowed for differentiation in performance of the various exterior wall assemblies.  The range of fire behavior seen in testing enabled the technical working group to draft performance metrics. To date, a formal ASTM ballot has been released that received several comments and feedback.

Energy-efficient design and technology often advance faster than fire and building safety codes and standards, which is sometimes at the cost of fire performance. Ideally, once the test method is published, it can be a candidate for inclusion into building, fire or residential codes as a requirement to demonstrate fire performance of new wall assemblies and/or retrofit solutions.  The current draft includes performance classifications based on the rate of fire spread.  At a minimum, this exterior wall performance information can inform builders and end users on their material choices. 

Could you provide some insights into the next steps or future initiatives in ensuring fire safety around energy-efficient technologies?

The immediate next steps for the project are for the IAFF to disseminate these findings to the fire service and develop educational materials.  The ASTM development of the new Standard is well underway and will continue through the normal proposal and balloting process. The ASTM initiative is being led by UL Solutions’ Dwayne Sloan, and the IAFF effort is being led by Sean DeCrane.   

This objective was initiated by the DOE to be exploratory in nature and to identify a path for evaluating fire performance of retrofit and innovative residential, energy-efficient wall solutions for the market.  This new test method will provide a means to evaluate flame propagation performance.

Areas of potential future study would be the interaction at the soffit, impact of penetrations (windows, doors, electrical outlets), and other potentially weakened breaks in the building envelope.  In terms of wall fire performance, the introduction of furring strips, furring strip gaps, the exterior application of insulation products are changing the fire behavior of the assembly and should be studied more closely to identify means of improving fire performance with minimal sacrifice of energy efficiency.

This article was originally published in the February 2024 issue of Fire & Safety Journal Americas. To read your FREE digital copy, click here.

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