Recent testing performed by McDowell Owens Engineering in Houston, Texas¹ (“McDowell Owens”) indicates that the same characteristics and properties of radiant barriers that make them so beneficial during the hot summer months also make them a significant fire hazard during a lightning storm. The evidence supporting these claims is already starting to mount in states like Texas, where a recent lightning storm produced no less than three confirmed lightning-induced radiant barrier fires in one area.

Fire and Lightning
To better understand why radiant barriers pose a significant fire hazard during lightning storms, one must first understand what a radiant barrier is and how it works. On a typical sunny day, radiation from the sun strikes the outer surfaces of one's home or building, causing those surfaces to heat up. One of the surfaces that absorbs the most radiation is the roof. When the roof heats up, it begins radiating heat inward toward the attic space, where it warms the attic floor. As the attic floor becomes hotter, it then radiates heat into the conditioned space of the structure, thereby making it harder and more expensive to cool. The radiant heat in the attic also affects the air-conditioning ductwork because it warms the cool air in the ductwork. When a reflective radiant barrier is installed on the underside of the roof decking, it reduces the transfer of radiant heat from the roof decking to the attic and the conditioned spaces by reflecting it back toward the roof. As a result, consumers who install radiant barriers typically see a significant reduction in cooling costs during those muggy months.

Radiant Barrier Foil Coverings
The most common type of radiant barrier on the market today is a radiant barrier foil covering. Although radiant barrier foil coverings come in many different configurations, they are all generally made the same way. Radiant barrier foil coverings usually consist of a thin sheet or coating of highly reflective material, usually aluminum foil, mounted or laminated to one or both sides of a substrate or a combination of substrates in layers. Common substrates include craft paper, plastic films, plywood sheathing, and oriented strand board. In new construction, builders will often purchase structural sheathing that has been pre-laminated with a coating of aluminum foil and paper. Because the pre-laminated radiant barrier sheathing can be installed like conventional roof sheathing, it reduces the need for additional labor during construction.

Unfortunately, pre-laminated radiant barrier sheathing is of very little use in older homes where removing and reinstalling the roof is usually not an option. Contractors tasked with retrofitting an older home with a radiant barrier system will often use a combination of radiant barrier products that may include aluminum foil pre-applied to both sides of a piece of rigid insulation or reinforced sheets of radiant barrier material that can be rolled out and draped between the roof rafters using staples.

Conductors of Electricity
Regardless of whether pre-laminated structural sheathing, pre-laminated rigid insulation, or reinforced sheets of radiant barrier material are used, it should come as no surprise that the aluminum laminate used in those radiant barrier coverings makes them an excellent conductor of electricity. It should come as even less of a surprise that a radiant barrier, attached to the under-decking of a roof system, has the potential to become grounded through incidental contact with the structure's electrical lines, plumbing lines, vent pipes, metal flashings, gutters, and HVAC lines and equipment. Once grounded, the radiant barrier has the potential to conduct electricity throughout the entire attic space.

In 2009, McDowell Owens performed a series of experiments with reinforced sheets of radiant barrier material to determine what would happen if a grounded radiant barrier became energized through contact with an exposed electrical conductor.² What it observed was that, as current began to flow through the radiant barrier material, intense heating occurred at the staples, followed by electrical arcing.³ The heating and arcing immediately ignited the combustible substrate materials upon which the aluminum foil was mounted. In 2010, McDowell Owens conducted additional experiments to observe how a grounded section of pre-laminated radiant barrier structural sheathing would react when energized and heated by an electric current flow of 50 amps.⁴ The results were almost identical. As the electrical current flowed through the radiant barrier, intense heating and fire were observed at the spot where the plywood clip joined two pieces of pre-laminated radiant barrier structural sheathing.⁵ McDowell Owens' experiments proved that, when a grounded radiant barrier is energized, it will catch fire. This begs the question as to how a radiant barrier installed on the underside of the roof decking becomes energized.

A Force of Nature
Enter lightning, one of the most powerful forces in nature. A single bolt of lightning can carry a charge well in excess of 30 million volts and produce an electrical current of anywhere between 10,000 and 200,000 amps. It is not difficult to imagine what would happen if a radiant barrier became completely or partially energized with an electrical current of 10,000 amps or more as a result of a direct lightning strike. More importantly, one no longer needs to imagine what would happen as there are plenty of real-life examples to illustrate just how devastating the damage can be when a radiant barrier system, charged by lightning, catches fire.

While lightning-induced radiant barrier fires are much more likely to occur in southern states where radiant barriers are more popular and where severe lightning storms are more prevalent, the evidence is clear that any structure with a radiant barrier is potentially at risk during a lightning storm. If that is correct, then why is so little information available about the potential hazards associated with lightning-induced radiant barrier fires? The answer is simple: Because the radiant barrier is typically the first material ignited and easily consumed by fire, many fire origin and cause experts unfamiliar with lightning-induced radiant barrier fires fail to recognize it as a potential ignition source.

More importantly, many of the individuals and investigators involved with handling these losses make the mistake of assuming that a fire following a lightning strike is nothing more than an “Act of God” and cut the subrogation investigation short. Our firm's own experience with lightning-induced radiant barrier losses, as well as that of McDowell Owens, strongly suggests that there are more lightning-induced radiant barrier losses that are not being properly identified or are simply being overlooked.

Fire Scene Investigation
In every claim where a lightning strike is alleged to have caused a fire and a radiant barrier is present, a thorough fire-scene investigation should be done by someone familiar with lightning-induced radiant barrier fires. Questions should be asked to ensure that the radiant barrier has been considered as a potential cause of the fire. Similarly, one should not make the mistake of assuming that, just because a building equipped with a radiant barrier was struck by lightning, the radiant barrier was the cause of the fire.

A thorough analysis of the fire scene, beginning with the identification of the lightning bolt's strike point, must be performed to establish the actual cause of the fire and to eliminate other products that may also be susceptible to lightning-induced fires. Subrogation counsel and experts familiar with lightning-induced radiant barrier losses and other lightning-induced product fires should be consulted to make sure one is getting the very best guidance about how to proceed with the fire investigation and potential subrogation claim.

¹ Ron Simmons, P.E., Eric Benstock, P.E., Rick Bonyata, P.E. and Nestor Camera, Special Report: Reflective Radiant Barriers, Fire Findings, Summer 2009, Vol. 17, No.3 at 7; McDowell Owens Engineering, Inc., Reflective Radiant Barriers: Good for Energy Savings – Bad For Fire Safety, mcdowellowens.com, November 5, 2010.
² Simmons, et. al., supra note 1, at 10
³ Id at 11.
⁴ McDowell Owens, supra note 1.
⁵ Simmons, et. al., supra note 1, at 12.