Prepare for the growing risk of damaging hail

While hurricanes and tropical storms have earned their fearsome reputations, increasingly frequent severe convective storms are the leaders in property damage. Powerful thunderstorms and squalls can boil up virtually anywhere on the continent, although the Great Plains of the central U.S. are ground zero for some of the worst. Especially during the spring and summer months, thunderheads spawned by the sun’s energy rise miles high, dragging warm, moist air into the stratosphere on powerful convective currents. Convective storms can birth dangerous lightning, massive downpours, devastating tornadoes, and even straight-line winds briefly rivaling the power of a tropical storm. However, when it comes to property losses to businesses, homes, schools, vehicles and more, no single feature of severe convective storms can match the toll exacted by hail.

According to data compiled by Aon, a major, global insurance broker, hail-related insured losses between 2000 and 2019 averaged between $8 billion to $14 billion a year.¹ During 2020, the National Oceanic and Atmospheric Administration’s (NOAA) Severe Storms database recorded 4,611 major hailstorms.² By one recent estimate, more than 6.2 million U.S. properties were affected by one or more hail events in 2020.³

The sky is falling

Hailstones form when moist, warm air rises into the upper atmosphere on powerful convective wind currents, allowing water vapor to freeze around specs of dust. As ice particles grow heavier, they fall to lower altitudes where strong winds may lift them higher once again, collecting more layers of ice. The cycle continues until the hailstones are too heavy to remain airborne and fall with varying levels of force, depending on their size. And the size can be truly astonishing. Following an April 28, 2021, hailstorm in Hondo, Texas, hail experts from the Insurance Institute for Business and Home Safety (IBHS) coordinated with the National Weather Service office in San Antonio to perform a three-dimensional scan of a hailstone measuring 6.4 inches in diameter and weighing 1.26 pounds.⁴ Imagine the damage such an object might cause to a rooftop HVAC unit, a car windshield or, even worse, and unprotected individual.

With many experts predicting that changing weather patterns will generate more recurrent and powerful convective storms, it is likely that major hail events will become more frequent and damaging. As a result, businesses may need to adjust to a future in which the potential for severe hail damage will be an ever-present and growing possibility.

Mitigation – Before the storm

Knowing what your vulnerabilities may be prior to a hail event is critical to understanding the potential impacts it might have on your business. Hail can damage any unshielded building feature, including:

• Roof coverings
• Roof-mounted equipment
• Skylights and other glazing systems
• Photovoltaic power generating systems
• Outdoor storage

Depending on age and condition prior to a severe hailstorm, the roof assembly will be the most vulnerable aspect of any commercial building. Over time, weathering due to UV-degradation from sunlight; wind forces; temperature extremes; expansion and contraction forces; contaminants; and even foot traffic may seriously weaken the performance of roof coverings during a hailstorm and heavy downpour. Even in the absence of other factors, the age of the roof will be a key concern.

Damage resulting from hail can be mitigated and even prevented before it occurs by selecting roofing materials, assemblies and other components with adequate hail-impact ratings, or by providing ballast or pavers to give additional protection to the roof assembly.

Annual roof inspections are one of the best ways to ensure a roof assembly will perform well during a hail event. Studies of roof-related losses show that loss rates are much less for locations where annual, visual roofing inspections are in place and performed.

Another serious vulnerability a commercial building may have is roof-mounted heating ventilation and air-conditioning (HVAC) equipment. The most vulnerable equipment will be roof-mounted with exposed and unprotected coils and fins, such as those used by air conditioning units.

Exposed equipment commonly damaged by hail may include:

• Roof-mounted air-conditioning condenser coils, fins and fan blades
• Cooling tower fan blades and fill media
• Upright/vertical heat exchanger coils
• Make-up air unit/air handlers and exhaust vents
• Rooftop exhaust fans

The solution for protecting vulnerable rooftop equipment with exposed coils and fins will be to provide rigid hail guards of strong mesh or metal that will disperse the impact of large hail. Where heat transfer or air movement is a concern, the guards may be mounted at an angle (30-35 degrees) to allow for unrestricted airflow while protecting against hail impacts.

Roof-mounted skylights also represent serious weak points against hail. Skylight glazing materials most capable of withstanding serious hail impacts include:

• Acrylic
• Polycarbonate
• Tempered glass
• Laminated glass

Once again, the age of a skylight and the materials employed when first installed will be important concerns.

Special attention should also be given to roof drainage systems that may come under stress during a serious hailstorm and associated downpour. Ice damming from significant hail accumulation can back up rainwater even in well-maintained drainage systems. If a roof drainage system is already compromised by debris, leaves and other obstacles, the threat posed by temporary hail accumulation will be amplified.

Preparation – Darkening skies

A stormfront is approaching. Warnings have been issued over television, commercial and weather-alert radio frequencies that conditions are right for severe thunderstorms with the potential for large hail. It’s time to activate severe weather preparations.

• Remove and bring indoors any equipment or property that could become wind-driven projectiles in high winds.
• Whenever possible, cover or take other steps to protect vulnerable equipment that cannot be moved.
• If possible, move any vehicles indoors or to any available shelter. 
• Idle equipment that could be impacted by power surges or spikes; make sure any computer files being worked on are saved.
• Make certain that all personnel are indoors and in secure areas.

Response – The storm is here

If you are on the road:

• Stop driving and pull completely off the highway.
• If you see a safe place close by (a garage, carwash bay or service station awning), drive under cover if you can.
• Do not leave the vehicle until hail stops.
• If your vehicle is being hit by large hail, protect your eyes against the possibility of broken glass.
• Do not drive through deep, standing water.

If inside a building:

• Stay indoors, away from windows.
• Direct occupants to safe areas, as severe convective storms can produce tornadoes as well as hail.
• Do not exit the building until the storm passes and the danger is over.

If caught outside:

• Obviously, seek shelter immediately.
• If you are unable to protect your entire body, do your best to protect your head from hail impacts.
• Be aware that sheltering under trees is risky; trees may lose limbs during severe storms and present elevated lightning risk.
• Be cautious about low-lying areas that may be subject to flash flooding.

Recovery – Assessing the impact

• Once the storm is over, safely perform an immediate inspection of any damage to your property.
• Check for ice dams in gutters and drains that could cause rainwater to back up on your roof deck.
• Inspect roofing for hail damage that may allow leaks into your building.
• Inspect building exterior and siding for hail damage.
• Check all windows and skylights for damage.
• Inspect roof-mounted HVAC and electrical equipment.
• Carefully remove any branches or limbs that may present risks to employees and others on your property.
• Reach out to contractors with whom you have relationships to ensure you will be promptly scheduled for necessary repairs.
• Notify your broker and insurance carrier that your facility has experienced storm damage.

Winds of change

Changing weather patterns and trends suggest that strong convective storms may become more frequent, stronger and potentially damaging, which means hail events may become more damaging in the future. Understanding the risk potential presented by hail, historically the costliest severe weather event on an annual basis, can help your business recover and build resilience when the sky falls.

Visit the Convective Storm Resource Hub for additional articles offering insights on how to help mitigate, respond to and recover from tornados, lightning and convective storms.

1. Climate & Catastrophe Insight: 2020 Annual Report. Aon. 2020.
2. “Facts + Statistics: Hail.” Insurance Information Institute, Inc. 2021
3. “The Hail Hazard and Its Impact on Property Insurance.” Verisk. 2021.
4. Erdmann, Jonathan. “Texas Hailstone, Over 6 Inches in Diameter, Confirmed as New State Record.” The Weather Channel. 24 June 2021.