Why This Research Matters 

Hail damage is one of the costliest weather-related risks for homeowners and insurers. While large hailstones are known for their destructive power, smaller “sub-severe” hail events—hailstones less than 1 inch in diameter—occur much more frequently and may quietly degrade asphalt shingle roofs over time.  

To better understand this overlooked hazard, IBHS launched a multi-year research program to study how frequent, small-hail events contribute to the long-term durability and performance of asphalt shingles. Using controlled lab impacts and field-informed testing, this work explores how cumulative damage from smaller hail contributes to early aging and increased vulnerability to future storms.  

Key Findings 

• Frequent small hail causes cumulative damage: Repeated exposure to small hail can significantly reduce a roof’s resistance to subsequent large hail events. 
• Accelerated aging: Sub-severe hail knocks away protective granules from asphalt shingles, exposing the underlying asphalt to sunlight and weathering—speeding up the aging process. 
• Higher vulnerability over time: Roofs exposed to both natural weathering and two simulated sub-severe hail events became up to ten times more susceptible to damage from later large hail impacts compared to new shingles. 
• Testing gaps: Current testing standards do not assess performance durability over time and to different concentrations and size distributions of hail. 

Takeaway 

The frequency and concentration of sub-severe hail are hidden but critical factors in asphalt shingle performance and roof longevity. Understanding this cumulative effect is essential for improving product design, testing standards, and risk modeling across the roofing and insurance industries. 

Together, these studies underscore that roof aging and repeated exposure to small hail are integral to understanding real-world roof performance.