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Protecting structures against damage from hailstorms often starts at the very top.

Roofs and various rooftop elements-such as skylights and heating, ventilation and air conditioning units-often sustain the most serious damage when hailstones strike, say loss control experts.

Adequately protecting a structure's roof from damage can save more than roofing material, though. If a roof is damaged or destroyed, the contents of a warehouse, office or other commercial structure often are also exposed to the elements.

Not only is damage done to the structure itself, but contents also can be damaged if water inundates them because of roof damage, explained Mike Burke, vp and chief engineer at Allendale Mutual Insurance Co. in Johnston, R.I. In planning for hail, risk managers are trying to devise a plan that will protect contents, he said.

While hailstorms are not considered as threatening as hurricanes, earthquakes and some other natural perils, loss control experts warn against downplaying the exposure to hailstorm losses.

Hailstorms can cause hundreds of millions of dollars of damage in a few hours.

A case in point is a May 1995 hailstorm that raked the Dallas-Fort Worth, Texas, vicinity. The violent weather, which caused $700 million in insured property damage in Texas, came only a week after a storm packing grapefruit-sized hailstones slammed through the same area, causing about $275 million in insured property damage, which included damage to 78 American Airlines Inc. planes that had to be grounded for repairs (BI, May 15, 1995; May 8, 1995).

Five years earlier, a hailstorm struck the Denver area during rush hour and ultimately caused $625 million in insured property damage, according to the Property Claim Services division of the American Insurance Services Group Inc.

Major hailstorms in recent years also have struck Australia, Canada, Germany and Switzerland, according to natural hazards research by Munich Reinsurance Co.

Although there are ways to minimize hail damage to nearly all exposed property, risk managers don't always take the steps they can to mitigate the peril, said Mr. Burke.

"It almost always starts the same with any of these natural hazards: For years, people have come from the base that you can't do anything about these natural events," he said. But hail usually won't constitute a "terrible attack" on property if companies properly prepare for it, he added.

And risk managers can indeed prepare for hail, because it usually doesn't strike without giving some warning, said Paul Mircik, technical manager-property loss control services for AIG Consultants Inc., a New York-based unit of American International Group Inc.

There are certain predictors, such as humidity, temperature and Doppler radar, Mr. Mircik explained. But, he added, "whether you can predict directly when it's going to occur-once again, Mother Nature does what she does."

Unlike earthquakes and hurricanes, which often are localized events, hailstorms can strike a wide swath of the country.

"From time to time, there are situations on the the East Coast as well as the West Coast, but for the most part, it would be in the central states," said Mr. Mircik. Hail usually accompanies tornadoes and large thunderstorms and is most common in spring, summer and fall. However, he said, it can strike in winter during snowstorms, as happened in New York during the Blizzard of 1996.

Experts point out that loss control for hail damage generally starts with the roof.

"One of the greatest concerns involves the roofs of industrial buildings," said Dennis Anderson, vp and director of engineering for Protection Mutual Insurance Co. in Park Ridge, Ill. The traditional built-up insulated steel deck roof has hail protection in the form of a gravel surface, said Mr. Anderson. But some newer designs use various membrane systems that cannot be covered with gravel, he said. Some unreinforced membrane roofs, therefore, can sustain severe damage during hailstorms, he said.

Older roofs often sustain more damage than newer ones in a hailstorm, said Steve Sachs, senior vp and manager-risk management services division of Hobbs Group, a brokerage and consulting unit of Arkwright Mutual Insurance Co. That is because over time, roofs get brittle because of prolonged exposure to extremes of heat and cold, said Mr. Sachs, who also serves as risk manager for the Rouse Co., a Columbia, Md.-based real estate development company.

About 40% of all structures Fort Worth owns were damaged in the May 1995 hailstorm, said Sue Nagle, risk management specialist for the Texas city. The damage ranged from minor to extremely severe, requiring roof replacement for some structures, she said. In all, the storm caused $11.5 million in damage to city property.

The total included about $500,000 in uninsured costs to repair city-owned vehicles. Damage to buildings was covered by the city's $100 million property insurance program underwritten by Hartford, Conn.-based Hartford Fire Insurance Co. (BI, May 15, 1995). The coverage was in excess of the city's $100,000 self-insured retention for hail, which was increased to $250,000 as a result of the loss.

Lexington Insurance Co. is the city's current primary insurer in a multilayer program, underwriting the first $5 million over the city's self-insured deductible, which is $50,000 for fire and $250,000 for hail, said Ms. Nagle. Westchester Fire Insurance Co. underwrites the next $10 million layer, Fireman's Fund Insurance Co. of Ohio underwrites the next $15 million, Travelers Indemnity Co. underwrites the $30 million to $100 million layer, and Allianz Insurance Co. writes stop-loss insurance to $300 million, she said.

To mitigate damage, Fort Worth now is converting all roofs that can be converted to two-ply modified bitumen, a roofing material, said Ms. Nagle. The two-ply roof protects the structure because when it's damaged by hail, the interior of the structure doesn't sustain damage. Also, building insulation isn't damaged. Although the two-ply roofing costs about 35% to 50% more than a single-ply roofing, the city considers it cost-beneficial, she said.

Allendale's Mr. Burke noted that manufacturers have developed stronger roof covers for buildings in the part of the country most vulnerable to hail, notably the area drained by the Mississippi River system.

For older buildings, he recommends maintaining a thin layer of gravel, which also supplies a small amount of fire resistance as a bonus.

"I can't think of a time when an approved covering had a problem," he said, referring to coverings that meet standards approved by Norwood, Mass.-based Factory Mutual Engineering & Research Corp. Dick Davis, manager-construction section at Factory Mutual Research, said the facility performs tests to classify roofing materials as being able to withstand either moderate hail or severe hail.

Roofing materials and flashing should be applied and maintained in accordance with industry standards, such as those set by the National Fire Protection Assn., said AIG Consulting's Mr. Mircik. The standards recommend coverings of gravel and slag to reduce hail damage.

Mr. Mircik also recommends regular roof inspections, preferably on a quarterly basis, to assure adequate protection.

After hail strikes, roof drainage systems should be cleared as quickly as possible, particularly if they aren't designed for heavy snow loads, said Protection Mutual's Mr. Anderson. Heavy hails can plug up drains, flooding the roof, which in turn can lead to a collapse, he explained.

Another feature of some roofs-skylights-present a unique exposure.

Skylights are a "negative" from a hail loss prevention standpoint, said Mr. Anderson. He said the best protection is simply not to have them.

AIG Consulting's Mr. Mircik suggested using protective screening to prevent damage to skylights.

Protective screening also mitigates the hail peril to HVAC units, said Mr. Burke of Allendale. Even if hail penetrates the screening, the screen slows down the stones' speed and, thus, their potential to inflict damage.

Fort Worth installs hail screens on condenser coils of HVAC units on roofs to deflect hail from damaging the units, Ms. Nagle said. This saves the city thousands of dollars because labor costs alone can run into hundreds if not thousands of dollars to replace the units, she said. The process of installing hail screens, which began 10 years ago, still is under way.

Glass is, of course, also extremely vulnerable to hail-and not only in terms of breakage, noted Mr. Sachs of the Hobbs Group. After a Rouse property sustained damage during the Fort Worth hailstorm, Mr. Sachs had windows closely examined for scratches. Scratches can weaken windows, making them more subject to subsequent damage from wind and other stresses, he said.

Corporate fleets of the automotive and aviation variety also face the prospect of hail damage. But the approaches to protecting vehicles can vary considerably.

"Our airplanes are all hangared" anytime they're not being used, said Judith Payne, risk manager for the state of South Dakota in Pierre.

Motor vehicles can be another story, though, she explained. "They're located all over the state in pools," she said. There are no buildings or means of moving them into buildings when a hailstorm strikes some locations, she said. Unless there are broken windows or damage that affects the driveability, the state doesn't repair hail damage to the bodies of its vehicles, she said.

Fort Worth's Ms. Nagle said the city sustained about $3.5 million in damage to its automobile fleet as a result of the 1995 hailstorm. It spent about $500,000 replacing windows and performing body work on selected vehicles, but otherwise allowed the damaged vehicles to be retired and replaced through attrition.