Examination Standard 4475, Steep Slope Roof Covers, has been updated to include Very Severe Hail (VSH) testing as part of FM Approvals’ commitment to testing roofing materials against the perils of evolving climate risks.
To receive a VSH rating, steep slope roofing materials must possess adequate physical properties to demonstrate impact resistance performance as it relates to hailstorms when evaluated to ANSI FM 4473, American National Standard for Impact Resistance Testing of Rigid Roofing Materials by Impacting with Freezer Ice Balls. Testing is used to grant ratings of Class 2, 3, or 4 while a modified version of ANSI FM 4473 is used to grant a VSH rating.
The Impact Resistance Test Apparatus consists of a launching device capable of propelling simulated hail (ice balls) at speeds necessary to develop the intended kinetic energy. Here are the requirements for Classes 2-4 as well as VSH;
|
Class |
Nominal Ice Ball Diameter (in. [mm]) |
Kinetic Energy |
Kinetic Energy |
|
2 |
1-1/2 (38.1) |
7.77 (10) |
8.55 (12) |
|
3 |
1-3/4 (44.5) |
14.95 (20) |
16.5 (22) |
|
4 |
2.0 (50.8) |
26.81 (36) |
29.5 (40) |
|
VSH |
2.0 (50.8) |
53 (72) |
58 (79) |