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Severe weather events in the United States have caused substantial financial losses for insurance companies in recent years. Among these events, hailstorms have notably contributed to roof system replacements, especially for asphalt shingle roofs, which are prevalent in over 75% of single-family homes nationwide. When homeowners undertake roof replacements, they rely on roofing contractors for expert advice on selecting suitable products, placing their trust in their recommendations.
Recognizing the need to educate insurers, roofing contractors, and consumers, the Insurance Institute for Business & Home Safety (IBHS), a nonprofit scientific research organization funded by the property insurance industry, has dedicated significant efforts to gather data and assess the relative performance of impact-resistant-labeled asphalt shingles.
To evaluate building components and structures, including asphalt shingles, IBHS conducts comprehensive tests, recreating real-world severe weather conditions such as wind, wind-driven rain, hail, and wildfires.
Recently, IBHS has developed a novel and peer-reviewed hail impact resistance test methodology, establishing a more accurate correlation between laboratory testing and real-world performance against hail. This method has been utilized to evaluate commonly available impact-resistant asphalt shingles, and the resulting performance ratings have been documented in IBHS’s comprehensive publication, “Roof Shingle Hail Impact Ratings.”
These test protocols and performance assessments serve as valuable resources for consumers seeking high-performing products, roofing contractors aiming to differentiate themselves in the market, and manufacturers striving to enhance the quality of their offerings.
Understanding and Evaluation of Impact-Resistant Asphalt Shingles for Hail Protection
Hail poses a significant risk to roofs across the United States, particularly in regions east of the Rocky Mountains, where strong thunderstorms can occur. While all asphalt shingles initially provide some level of hailstone impact protection, impact-resistant shingles are marketed as offering superior performance during hailstorms. However, not all products labeled as impact-resistant demonstrate equal effectiveness. Consumers deserve the assurance that impact-resistant shingles deliver on their marketing claims.
Two types of impact-resistant shingles exist. The first type employs a traditional manufacturing method that incorporates mesh or scrim reinforcement on the underside of a standard oxidized asphalt shingle. The second type involves modifying the asphalt with polymers, recently gaining popularity.
To assess impact resistance, impact-resistant shingles must pass one of two standardized tests: UL 2218, “Impact Resistance of Prepared Roof Covering Materials,” which utilizes steel balls, or FM 4473, “Specification Test Standard for Impact Resistance Testing of Rigid Roofing Materials by Impacting with Freezer Ice Balls,” which employs pure water ice balls.
Both tests are based on the correlation between hailstone diameter and kinetic energy and draw from research conducted in the 1930s, assuming that damage severity directly correlates with the kinetic energy of a projectile. The projectiles used in these tests range from 1¼ inches for Class 1 to 2 inches for Class 4.
In UL 2218, a steel ball bearing is dropped onto a roofing test panel from a height that replicates the theoretical kinetic energy of spherical hailstones with a similar diameter. Each target location is struck twice in the same spot, and performance is evaluated by visually inspecting the impact locations on the back side of the shingle bent over a mandrel for any cracks or tears under magnification. A pass-or-fail determination is then made.
In FM 4473, a pure water ice ball free of cracks and air bubbles is launched perpendicular to a roofing test panel at a speed that achieves the desired kinetic energy. Again, each target location is impacted twice in the same spot. Performance is evaluated visually from the top and bottom for any signs of cracking or breakage.
Similar to the UL 2218 test, a pass or fail designation is assigned to the product. However, it is essential to note that neither test accurately replicates the type and severity of damage typically observed on roofs following hailstorms. These test standards were developed before the material properties of natural hailstones were fully understood. While historical hail studies provided quantitative data regarding mass, diameter, and density, the strength or hardness of hailstones was only described qualitatively.
Advancing Hail Research: IBHS Field Studies and Innovative Techniques
To bridge the existing knowledge gap, the Insurance Institute for Business & Home Safety (IBHS) initiated a comprehensive field study in 2012 to gather precise quantitative data on hailstone properties and expand our understanding of this meteorological phenomenon. IBHS researchers actively pursued severe thunderstorms, collecting hailstones and conducting measurements of their mass, diameter, and strength.
To assess hailstones’ hardness or compressive strength, IBHS developed a specialized instrument to determine the force required to fracture a hailstone. This data has significantly enhanced our understanding of hailstone aerodynamics, their kinetic energy upon impact with the ground, the mass-to-diameter relationships, and their strengths.
Subsequently, IBHS created another innovative field instrument called an impact disdrometer. This device measures the energy imparted by hailstones on surfaces, enabling a comprehensive examination of hailstone size distribution and variations within a storm.
Deploying a network of disdrometers in advance of thunderstorms, IBHS captured data on the swaths of hail generated by these storms. A notable breakthrough was IBHS’s pioneering 3D laser scanning technology to create highly detailed digital models of natural hailstones. These models were then printed in three dimensions and subjected to controlled wind tunnel experiments, providing in-depth assessments of hailstone aerodynamics.
Through extensive data collection, IBHS has established the largest research-grade database of hailstone characteristics, encompassing thousands of hailstones and numerous observed storms. Analysis of this data has revealed crucial insights, such as the slight overall strength advantage of natural hail compared to pure ice, varying strength levels based on trapped air pockets during hailstone formation, and the existence of different impact modes due to this strength range.
Furthermore, the research findings have challenged long-held assumptions, including the disproven correlation between hailstone strength and density and the realization that existing test methods overestimate hail’s mass, fall speed, and impact energy.
IBHS collaborated with esteemed partners, including the National Center for Atmospheric Research, Penn State University, the University of Oklahoma, and Johannes Gutenberg University in Mainz, Germany.
This collaborative effort propelled rapid advancements in hail knowledge, redefining the relationship between hailstone size, fall speed, and energy. These breakthroughs have facilitated improvements in laboratory testing methodologies and laid the groundwork for developing a new test method to evaluate hail impact resistance better.
Advancing Laboratory Testing: IBHS’s Hailstone Replication and Impact Assessment
Equipped with field data and the resulting valuable insights, IBHS researchers have devised a laboratory method to replicate the properties of hailstones. This innovative approach is the foundation for a new test method capable of producing damage patterns that closely resemble those observed in natural hailstorms.
Initial proof-of-concept experiments utilized seltzer water and conventional injection molds to demonstrate the feasibility of creating ice with densities comparable to natural hailstones. The carbonation bubbles present in the water-trapped gas during the freezing process mimic the properties of hailstones observed in the field.
While successful, these early experiments proved inefficient and needed more controllability for practical laboratory testing applications. To address this challenge, IBHS collaborated with Accudyne Systems Inc., based in Newark, Delaware, to develop and patent a hail manufacturing system capable of mass-producing hailstones for testing purposes.
This system empowers IBHS researchers to finely control ice properties by adjusting the diffused carbon dioxide amount, gas diffusion pressure, temperature, and freeze time. As a result, the manufactured ice replicates the diverse range of hailstone strengths observed in the field.
The hail manufacturing system can accommodate molds that produce hailstones ranging from 1 to 4 inches in diameter. The damage inflicted by these laboratory-manufactured hailstones closely resembles the effects caused by their natural counterparts.
Through this meticulous replication of hailstones in a controlled and repeatable manner, IBHS researchers have identified three impact modes when hail strikes a roof:
- Hard bounce impact: The hailstone bounces off an asphalt shingle while remaining largely intact.
- Hard shatter impact: The hailstone fractures numerous pieces, leaving no ice remnants on the shingle.
- Soft impact: The hailstone turns into slush upon impact with the shingle.
These distinct impact modes arise from variations in the strength and density of hailstones observed in real-world scenarios. The two hard impact types often result in granule loss, shingle deformation, dents, breaches, or tears. Soft, slushy impacts also lead to granule loss but leave less noticeable deformations.
Each of these damage types can compromise the functionality of a shingle. Dents and tears may enable water penetration, compromising the shingle’s ability to shed water and potentially allowing it to reach the underlying deck, posing a risk of interior water damage.
Granule loss exposes the asphalt to ultraviolet radiation, leading to degradation, increased brittleness over time, and a potential reduction in the shingle’s fire resistance classification. These factors can shorten the lifespan of an asphalt shingle roof system and make it more vulnerable to subsequent hailstorms.
IBHS Impact Resistance Test Protocol: Enhancing Evaluation Standards for Asphalt Shingles
In its commitment to promoting superior product performance and setting higher benchmarks, IBHS has developed the IBHS Impact Resistance Test Protocol for Asphalt Shingles. This comprehensive protocol defines the laboratory testing method and criteria for assessing the impact resistance of asphalt shingles using meticulously manufactured hailstones.
The resulting IBHS asphalt shingle hail impact ratings are based on the outcomes obtained from 2-inch hailstones. To accurately replicate the kinetic energy of natural hailstones concerning their diameter, a hail cannon is employed to launch hailstones perpendicularly at roofing test panels, ensuring that the impact energy per unit area is maximized.
By utilizing perpendicular impacts, representing the most severe impact scenario for a shingle, the IBHS test protocol provides a stringent evaluation of shingle performance.
The IBHS test panel aligns with the configuration specified in the UL 2218 test method, encompassing a 3-by-3-foot frame with a central structural element that simulates a roof rafter or truss. The panel includes a plywood deck, underlayment, and shingles installed following manufacturer instructions. Notably, the shingles used in testing are procured through the distribution chain, mirroring the process followed by roofing contractors and homeowners.
The IBHS test method encompasses the following key aspects:
- For three-tab shingles, a minimum of 20 impacts per hailstone size is required.
- For architectural shingles, 40 impacts per hailstone size are required, with 20 impacts focused on single and 20 on multi-layer portions.
- Impacts are concentrated on the primary field of the shingles, excluding edges, joints, corners, outer types of frame, and the middle structural member.
- The IBHS test protocol mandates a single impact at each targeted location to ensure precise observation of damage caused by the initial impact, as subsequent impacts could mask the true extent of the damage.
- Equally distributed hard and soft impacts are conducted for each hailstone size, with a slight allowable variation between hard shatter and hard bounce modes. This approach guarantees a realistic assessment of a product’s performance under diverse impact conditions.
The IBHS Impact Resistance Test Protocol establishes a rigorous and comprehensive methodology, fostering accurate evaluations and providing stakeholders with realistic expectations regarding product performance.
Damage Assessment in the IBHS Test Protocol: Advancing Quantitative Evaluation Standards
The IBHS test protocol comprehensively evaluates three distinct damage modes to assess product performance thoroughly. These modes encompass the presence of tears, the volume of dents and ridges, and the area of granule loss. By capturing the diverse damages resulting from the different impact types, the protocol ensures an accurate differentiation of product performance.
To overcome the limitations of subjective pass-or-fail ratings in existing test methods, IBHS has developed an objective tool for damage evaluation. Collaborating with a software development company, IBHS introduced the Hail Impact Parameterization System—a sophisticated image-processing tool.
This system utilizes a series of meticulously captured photographs to create a precise 3D model of an impacted shingle, enabling the generation of accurate measurements for deformations, granule loss areas, and other damage indicators.
The Hail Impact Parameterization System can quantitatively measure dents, ridges, individual granule loss, and patch granule loss areas. By collecting these quantitative measurements, the damage assessment transcends the binary pass-or-fail classification and provides a quantitative rating of damage severity. Expert judgment is applied to evaluate the third damage mode, which is visually assessed and assigned a severity level.
In the IBHS test protocol, the damage evaluation is conducted from the top side of the shingle, replicating the viewpoint of roofing contractors and insurance adjusters assessing roof systems after a hailstorm.
For each hailstone test size, a severity score is determined for each of the 20 impacts (for three-tab products) or 40 impacts (for architectural products). These severity scores are averaged to calculate an individual impact severity score. Subsequently, all individual impact severity scores are averaged to determine a product’s overall performance evaluation rating. This meticulous averaging process instills greater confidence in the product’s performance capabilities than in previous standardized tests.
By implementing a robust and quantitative damage assessment methodology, the IBHS test protocol enhances evaluation standards, facilitating more precise and reliable assessments of product performance.
Shingle Ratings and the Ongoing Commitment to Performance Assessment
In April 2019, IBHS tested eight basic impact-resistant shingles to establish the test protocol and initial ratings. Subsequently, in June 2019, IBHS publicly released the protocol and ratings to provide consumers with valuable insights into product performance.
The ratings encompass performance and specific damage categories, including dents/ridges, tears, and granule loss. By offering ratings based on damage categories, homeowners and roofing contractors gain additional knowledge to inform their selection of asphalt shingles, considering their regions’ general hail characteristics.
Recognizing the evolving scientific understanding of hailstorms, IBHS acknowledges the importance of continually updating the ratings. As such, all products are scheduled to be retested every two years. New products will be assessed within six months of release to ensure the ratings accurately reflect the shingles installed across the United States.
Upon the initial release of the ratings in June 2019, one of the tested products received a poor rating. Within fewer than six months, that product was no longer available for purchase, illustrating manufacturers’ proactive response to improving their offerings. Among the initial ratings, five products were rated as good or excellent.
Over the subsequent two years, manufacturers further enhanced their shingle products, resulting in two additional scorecard updates that incorporated new offerings. In the first scheduled retest, conducted in June 2021, nine basic impact-resistant shingles were tested, with eight earning a good or excellent rating.
These advancements do not alter the performance of previously installed products; however, new construction and reroofing projects can benefit from incorporating the latest scientific knowledge by asphalt shingle manufacturers, thereby improving the resilience of roof systems.
The shingle performance ratings are integral to the IBHS FORTIFIED Home program, which assists homeowners in selecting more resilient roof systems. Shingles are rated good or excellent for use in IBHS FORTIFIED Home—High Wind & Hail-designated properties.
As hailstorms persist, the IBHS Impact Resistance Test Protocol for Asphalt Shingles will continue to provide manufacturers with crucial performance data and empower contractors with essential information for product selection in regions prone to hail events.
