FM’s VSH Testing – Very Severe Hail

UPDATED AUGUST 2025

FM Global, a leading commercial building insurer, and its code-approved testing agency subsidiary, FM Approvals, have created a Very Severe Hail (VSH) impact resistance classification that could affect design professionals.

FM Global Guidelines
Traditionally, FM Global has recommended its insured building owners use moderate hail (MH) and severe hail (SH) classified roof systems for buildings located in areas FM Global considers to be susceptible to moderate or severe hail impacts. FM Loss Prevention Data Sheet 1-34 ("Hail Damage") provides a map identifying these regions. In recent years, the insurance industry in the United States has seen an uptick in losses from hail in terms of the number of claims experienced and costs of those claims. A majority of the hail damage occurs to roof systems and other rooftop components.

FM updated the VSH region in 2025 and increased the reach to now include all or parts of nine states including: Montana, Wyoming, Colorado, New Mexico, Texas, Oklahoma, Nebraska, Kansas, South Dakota, North Dakota, Minnesota, Iowa, Missouri, Arkansas, Louisiana, Mississippi, Tennessee, Illinois and Wisconsin.

 
Per FM Global, this area was classified as a VSH region based on data from the National Oceanic and Atmospheric Administration's National Weather Service and National Center for Environmental Protection's Storm Prediction Center. This data shows a concentration of reports of hail greater than 2 inches in diameter in this geographical region.

Hail Classifications
FM Approvals traditionally has tested and classified membrane roof systems for MH and SH impact resistances using FM 4470 ("Approval Standard for Single-Ply, Polymer-Modified Bitumen Sheet, Built-Up Roofs (BUR) and Liquid Applied Roof Assemblies for use in Class 1 and Noncombustible Roof Deck Construction). This is the same test method on which many FM Approvals roof system classifications are based.

Using FM 4470's procedure, MH-classified roof systems withstand a 2-inch-diameter steel ball weighing 1.19 pounds dropped from a height of 81 inches in a section of tubing. This results in an impact energy of about 8 foot-pounds (ft-lbs.) on the surface of the roof system test specimen.

SH-classified roof systems withstand the same 2-inch-diameter steel ball dropped from a height of 141.5 inches, resulting in an impact energy of about 14 ft-lbs. on the surface of the roof system test specimen.

FM Approvals recently updated its impact-resistance test method to include testing for the VSH classification. The new testing involves propelling 2-inch-diameter preformed ice balls at roof system test specimens using an ice ball launcher. The ice balls are propelled at 152 to 160 feet per second, resulting in an impact energy of 53 to 58 ft-lbs. on the surface of the roof system test specimen.

Carlisle’s VSH Cover Boards
With these higher test standards, new materials and assemblies are being developed and tested to meet the new ratings. Carlisle SynTec Systems has a variety of cover boards that can assist with meeting the needs of VSH systems

SecurShield^® HD Composite is a composite insulation panel comprised of ó” HD polyiso cover board laminated to SecurShield rigid polyiso insulation. This 2-in-1 solution allows for minimum R-values to be met in conjunction with a cover board solution.

StormBase^® Composite is a rigid-roof insulation composite panel composed of a polyiso insulation panel manufactured on-line to 7/16” OSB.

DensDeck^® StormX Prime is a reinforced gypsum cover board with an enhanced moisture-resistant core and coated glass mat facers.

DEXcell^® FA VSH Glass Mat roof board features a reinforced gypsum panel with an enhanced gypsum core and heavy duty coated glass mat facers.

EcoStorm VSH™ is an engineered composite panel made from a blend of plastic and cellulose fiber sourced from post-industrial and post-consumer waste streams.