DisasterSafety — Protect Businesses from Hail Damage

DisasterSafety - Protect Businesses from Hail Damage

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 hail storms. 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.

Understanding Hail Damage Resistance Ratings

IBHS created two maps illustrating hail storms 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

DisasterSafety - Protect Businesses from Hail Damage

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 hail stone 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 hail storms.

IBHS recommends the use of products with a UL 2218 Class 4 or FM Global 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 hail storms (storms with a maximum hail stone of 1-inch or larger).

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