Today’s IBHS Study Just Changed the Game on Hail Damage: How Small Hailstones May Be Quietly Destroying Roofs
For over a decade, insurance carriers and their so-called preferred "independent" engineers have insisted that only “severe” hail — typically defined by the National Weather Service as stones over 1 inch in diameter — pose a real threat to asphalt shingle roofs. This rationale has been the foundation for countless denials of hail damage claims to residential and commercial roofs after storms labeled “sub-severe.” But a landmark 10-year research effort by the Insurance Institute for Business & Home Safety (IBHS), detailed in a study released today, directly rebuts this long-held assumption. The data clearly demonstrates that smaller, more frequent hailstorms can actually pose the greatest long-term threat to your roof.
The IBHS study shows that repeated exposure to high concentrations of sub-severe hail — hailstones between 0.7 and 1 inch in diameter — can accelerate the aging of asphalt shingles to an astonishing degree. Using a series of meticulously controlled lab experiments, researchers simulated dense, repeated hail events and interspersed them with natural weathering processes to mimic real-world exposure. Within just two years, the shingles subjected to these tests performed like materials that had naturally aged for a full decade.
One of the key mechanisms of this accelerated aging is granule loss, a critical factor in shingle degradation. Granules aren’t just cosmetic — they shield the asphalt layer from UV radiation, temperature cycling, and moisture infiltration. Once dislodged, the asphalt becomes exposed and begins to deteriorate rapidly. According to the study, the cumulative granule loss from just two rounds of sub-severe impacts exceeded that caused by a single strike from a 2-inch hailstone, which has traditionally been seen as the benchmark for functional damage.
But the problem doesn’t stop there. The study also evaluated the performance of naturally weathered shingles subjected to the same barrage of small hail. These aged shingles were found to be nearly ten times more vulnerable to damage than new or well-preserved ones. This finding is particularly important because it means that roofs previously exposed to sun, rain, and other natural elements — even without prior hail damage — become significantly more susceptible to failure when small hail strikes again.
Technical imaging and machine vision algorithms were used to quantify granule loss with pixel-level precision, and impact testing with calibrated hail cannons mimicked the real-world speed and energy of natural hail events. The resulting data reinforces the study’s conclusion: frequency, not just size, matters. Sub-severe hailstorms are far more common than large hail events and can cause cumulative, irreversible damage over time — damage that may go unnoticed until it leads to a full roof failure.
IBHS’ 2025 study cited and appeared to build directly on a 2021 study titled New Asphalt Shingle Hail Impact Performance Test Protocol and Damage Assessment, which established the IBHS Impact Resistance Test Protocol. In brief, the 2021 work introduced laboratory-manufactured hailstones engineered to mimic key properties of natural hail—most notably realistic density (approximately 0.2–0.9 g/cm³) and compressive strength. The 2025 study applied that same protocol for large-hail (2-inch) impacts and extended the methodology to sub-severe sizes, calibrating velocity/kinetic energy and using high impact densities to reflect real storms. Notably, the 2021 paper called for field validation of lab findings; the 2025 study answered that call by incorporating field observations to define a “high-concentration” scenario of roughly 44 impacts per square foot—while documenting that actual storm microbursts can produce far greater strike counts over short intervals. Stated differently, real-world small-hail exposure can exceed laboratory test levels, meaning the potential for cumulative damage on actual roofs may be even higher than controlled testing suggests.
This research puts pressure on the insurance industry to update outdated assessment models and consider cumulative damage from small hail events as legitimate grounds for coverage. Policyholders should be prepared to challenge denials based solely on hail size and lean on this peer-reviewed study as compelling scientific evidence.
In light of the findings, property owners — especially those in hail-prone regions like Texas — are strongly encouraged to document all hail events, regardless of official severity, and seek professional evaluations from roofing experts or licensed public adjusters. As we previously discussed in our article, When to File a Commercial Hail Damage Insurance Claim for Your Roof in Texas – And Why Timing Matters More Than You Think, hesitation can be costly. Every delay after a storm gives insurers more ammunition to deny valid claims — especially when damage from multiple small storms adds up over time.
Small hail may look harmless, but this study proves it can quietly carve years off the life of your roof. Don’t wait for the next “big one” — the real damage may already be happening, one small storm at a time.