Reduce Hail Damage to Businesses

Significant hailstorms result in millions—and sometimes billions—of dollars in damages to commercial roofs, siding, and outdoor and roof-mounted equipment.

When it comes to choosing the right roof for your business in a hail-prone area, IBHS research found there is considerable variation in the impact resistance of different types of roof coverings. Lab tests and field observations indicate that most commercial roof coverings are not typically damaged by hail less than 1.25 in. in diameter, however, 3-tab asphalt shingles may be damaged by hail as small as 1 in.

Extensive damage has also occurred to outdoor and roof-mounted equipment as a result of hailstorms. Aging and weathering can accelerate the deterioration of non-impact-rated skylights and make them become brittle, increasing their vulnerability to cracking, leakage, and shattering from hail.

If the IBHS maps listed below indicate your business is located in a hail-prone area, it is important to take this into consideration when installing a new roof, mounting equipment on the roof or making other improvements to the building.

Hail Damage Overview

Roofs are the most frequently damaged part of a building due to hail. Almost all kinds of roofs can sustain hail damage. On an asphalt shingle roof, hail damage may look like dark spots, or there may be holes, cracks, tears or bruises. Metal, tile, slate, wood shake, built-up, and membrane roofs also can be damaged by hail, with each material showing somewhat different signs.

Hail damage is usually characterized as either functional or cosmetic.

Functional damage affects roof performance and should be repaired promptly, since diminished performance can lead over time to water damage, mold, or rot.

Cosmetic damage affects the appearance but not the function of the roof.

To determine the type and extent of suspected hail damage, it is important to hire a qualified inspector to inspect the roof, assess the damage, and recommend a plan for repair. It is also important to contact your insurance company promptly, and if possible, make temporary repairs to reduce further damage. Be aware that coverage may vary depending on the policies of different insurance companies, and circumstances of the damage.

Understanding Hail Damage Resistance Ratings

IBHS created two maps illustrating hailstorms in the last decade and in the last 55 years to help identify areas at risk from hail damage. The first map, featured here, shows the occurrence rate for hail with a size of 1 in. and greater over a 10-year period beginning in 2000. This map shows areas with the most frequent occurrences of damaging hail over the last 10 years.
For many years it has been common knowledge that certain roofing materials provided better protection against hail damage, however no defining standard existed. Consequently, in 1996 Underwriters Laboratory (UL) developed the UL Standard 2218, “Impact Standard for Impact Resistance of Prepared Roof Covering Materials.” While IBHS does not have claim data for commercial buildings, closed claims studies for residential structures have shown that homes roofed with shingles or metal roofing meeting this test standard are significantly less likely to have a claim after being subjected to a hailstorm that caused substantial damage to non-impact-rated roofs.

The UL 2218 classification set a standard for roof impact resistance whereby materials were rated on their resistance to impacts with steel balls simulating hailstones of various sizes impacting at terminal velocities. The classifications for impact resistance are expressed as Class 1, 2, 3 or 4, which relate to a roof covering’s ability to withstand impacts from 11/4, 11/2, 13/4 and 2 inch diameter steel balls, respectively. Impact-resistant roofing materials that are rated Class 4 provide the best resistance to damage.

More recently, FM Global developed a test standard using ice balls: Standard 4473, “Test Standard for Impact Resistance Testing of Rigid Roofing Materials by Impacting with Freezer Ice Balls.” The Classifications for impact resistance are similarly expressed as Class 1, 2, 3 or 4, which relate to a roof covering’s ability to withstand impacts from 1-1/4, 1-1/2, 1-3/4 and 2 in. diameter ice balls, respectively. As with UL, materials that are rated Class 4 provide the best resistance to damage. While this test standard was primarily developed for use with rigid roofing materials such as slate, clay, and concrete tiles, there have been attempts to apply it to other roofing products.

Low slope roof systems that have satisfactorily passed FM Approvals Class Number 4470 “Approval Standard for Single-Ply, Polymer – Modified Bitumen Sheet, Built-Up Roof (BUR) and Liquid Applied Roof Assemblies for use in Class 1 and Noncombustible Roof Deck Construction” actually pass several tests that include hail damage resistance. This comprehensive roof system Approval will include a rating of 1-MH, which is approved for moderate hail exposures or 1-SH, for severe hail exposures. This differs from FM Global Standard 4473, as4470 is a comprehensive roof system approval for the cover and deck including tests for hail, fire, wind uplift, water leakage, etc., while FM Global 4473 is solely assessing impact resistance for steep sloped rigid roof cover materials.

Choosing The Right Roof Covering

Select a hail impact-resistant roof for a new building or when re-roofing

The IBHS map, featured here, shows all counties where hail events with hailstone sizes greater than 2 in. have been reported over the past 55 years. Hail of this size will almost always cause significant damage. As is clearly indicated on the map, many counties in the U.S., east of the Rocky Mountains, have experienced these kinds of damaging hailstorms.

IBHS recommends the use of products with a UL 2218 Class 4 or FM Approvals 4473 Class 4 rating in hail-prone regions. The UL Online Certifications Directory maintains a list of UL Certified Clients for Roof Covering Materials, Impact Resistant, UL 2218. Click on a manufacturer’s file (far right column) to find out the class rating for their product.

To reduce hail impact damage to roof-mounted equipment, select equipment that is capable of withstanding hail impacts or install protection such as hail guards, shields and wire mesh. As with any roof related installations, if a hail guard or shield is installed on a roof, it should also be properly designed to resist estimated uplift pressures as defined by ASCE 7.

For more information on reducing the effects of hail impacts to low slope roofs, roof-mounted equipment, skylights, ductwork, and outdoor equipment, see FM Global Property Loss Prevention Data Sheet 1-34 – Hail Damage.

Based on hail reports compiled by the storm prediction center, counties highlighted in blue are subject to a high frequency of damaging hailstorms (storms with a maximum hailstone of 1-inch or larger).

Don’t Get Scammed

The property owner, not the insurance company, decides which contractor to hire to repair hail damage.

  • Be on the alert for fraudulent “storm-chasing” roof contractors who rush into an area after a major hailstorm and aggressively pressure building owners to hire them.
  • Scammers may offer to pay some or all of the owner’s property insurance deductible as purportedly “saving money”—which is illegal in many states.
  • Scammers may also insist on payment up front, and typically leave town after performing shoddy work—and sometimes without performing any work at all!

Hail Guards: Protection for Roof-Mounted HVAC Equipment

Just like a roof itself, roof-mounted heating ventilation and air-conditioning (HVAC) equipment can be severely damaged by hail, leading to energy loss and potential business downtime. Sometimes, the damage associated with a single hailstorm can cost a business much more than protecting the equipment in the first place. And in some facilities, the cost of downtime and lost productivity can be more devastating than the repairs or replacement of the equipment. Equipment commonly impacted by hail includes:

  • Roof-mounted units—condenser coils and fan blades 
  • Air-cooled chiller—condenser coils and fan blades
  • Cooling towers—fan blades and fill media
  • Upright/vertical heat exchangers—coils
  • Make-up air unit/air handler—exhaust vents
  • Rooftop—exhaust fans

Examples of Hail Damage

HVAC Fin and Coil Damage

(Photos courtesy of Air Solution Company)

Hail Guards Can Protect Your Investment

A cost-effective way to reduce damage is to add “hail guards” to roof-mounted HVAC equipment. Hail guards are specially designed protection systems that cover outdoor equipment components while allowing for adequate airflow. Although there are no standardized tests to compare the performance of specific hail guard systems, several common system designs seem to offer protection in many hailstorm scenarios.

Commonly, coil-based hail guard systems have an aluminum frame with a ½-in. by 1-in. woven mesh of galvanized wire or louvered panels. Guard brackets are held in place by screws that are mounted to an interior framing structure, allowing for easy removal for equipment servicing and maintenance. Semi-rigid composite material configured in either a “lattice” or “square” pattern is another cost-effective after-market solution for protecting the condenser coils.

Another effective method for protecting coils and cooling tower fill is using hail guard netting/intake filter screens. This system consists of an integrated galvanized framing system and a heavy-duty fiber-reinforced filter screen. These screens are designed to be very strong and durable for high volume/velocity HVAC equipment. Filter screens are available with or without the galvanized hail guard feature and can be used separately on all air-cooled chillers, condenser units, air handling units, louvers and cooling towers for airborne debris management. These systems help keep coils free of debris and maintain the overall system performance. 

Depending on the manufacturer, hail guards can be UV protected, rot resistant, weather resistant, and abrasion and corrosion resistant.

Rooftop Hail Guards

(Photos courtesy of Air Solution Company)

Hail Guard Netting

Retrofit Guards

While some hail guards are installed as part of a new equipment system, sometimes the hail guard is an optional feature that may be purchased at a later date for easy installation. It is also possible to retrofit existing equipment units. When determining if a retrofit is feasible, contact the roof-mounted equipment manufacturer to see if the current unit can be retrofitted. Due to the complexity and age of each individual unit, a representative may have to visit your site to take measurements before pricing and productions, or they will provide an easy tool that can be used to take measurements to provide to the manufacturer.

Installation and Maintenance Concerns

  • Guards should be installed and serviced only by qualified personnel, whether for new installation or retrofitting.
  • Guards should not be placed directly against fins.
  • Guards should be fastened securely to prevent movement during high-wind events.
  • Guards should be monitored for any reduction in airflow to minimize compressor failure.
  • Guards should be kept clean and free of debris.
  • Hail guard netting/filter screens are engineered for proper air movement and should not be substituted with window screens or mesh not specifically designed for this use.


While there are no standardized tests to compare the performance of hail guard systems, for businesses located in regions where hail is common, they are a prudent investment to reduce damage to critical roof-mounted HVAC equipment. Proper installation and maintenance is critical to making this investment pay off for your business.