As the weather becomes more severe across the country, roof systems need to be designed and installed with resilience in mind. In this article, we will explore types of hail classifications, FM Global designated hail zones in the US, and what you can do to protect your building from Very Severe Hail (VSH).
Usually, you think of a roof protecting your building from rain and water getting into your building. But when that rain freezes into hailstones, you are at risk of impact damage and leaks.
Hail size is commonly estimated by comparing the size of the hailstone to a known object that ranges from the size of a pea (1/4 inch in diameter) up to the size of a grapefruit (4 1/2 inches in diameter). However, within their 1-34 Data Sheet, FM Global, one of the world’s largest property insurers, classifies hail into three sizes: Moderate, Severe, and Very Severe Hail.
Typically, the phenomenon of hail occurs from May to September. According to FM Approvals, hailstorms increase during the summer when warmer temperatures lead to atmospheric instability and thunderstorms—most often in the mid-latitudes.
Read More: New Tools Can Help Reduce Losses From Hail
FM Global has designated hail zones in the US-based on the type of hailstones most familiar to the area. These zones are used when designing, specifying, and constructing buildings to ensure they can withstand hailstones without failure.
Originally, FM Global’s zone map released in 2014, when the concept of VSH was first introduced, encompassed a relatively small zone including three counties in Northern Texas, Oklahoma, and Kansas. In 2018, they expanded that zone to include nearly 25% of the Midwest (from North Dakota to Texas, and from Colorado to Missouri).
But these guidelines and hail zones are not only important for FM Global insurance customers, but non-FM Global customers also need to be aware of the VSH standard for their building location, as this information should still be helpful when choosing the right roofing system and design for their roof project.
FM Global has become the leader in establishing best practices for building protection; it’s common for non-FM Global customers to follow FM Global listings on RoofNav® as a baseline for their building and construction projects.
History has shown that hail can be extremely destructive, especially stones that are 2 inches or larger. Hail can pummel glass, plastic, siding, metal, as well as just about any type of roofing. Low-slope roofs are particularly vulnerable; due to the angle of the roofing system, a low-slope roof accepts the full brunt of the hail attack.
Hail damage to roof systems can include:
The larger the size of hail and the more intense the hail storm can lead to even more catastrophic damage to buildings.
The cost of hail damage to a roof system varies from a few thousand, for a roof repairs to hundreds of thousands of dollars, for a roof replacement. It’s no wonder building owners are seeking peace of mind, a resilient and durable roof system that will outperform its expected life cycle—and not just from hail.
While hail is a big concern in the FM VSH Zones, building owners should not discount other important performance attributes and design requirements, including:
A resilient roof system designed for hail performance is highly recommended, where significant hail events occur regularly as a measure to prevent losses. Having a resistant building envelope can help you withstand disruptions, fortify against breaches, and endure extreme conditions.
While FM Global’s hail standard and zone map might be somewhat new, FiberTite’s track record for outstanding performance in the face of severe events is not. The difference comes down to the integration of chemistry and fabric, plus the design team who stands behind our products.
There’s no telling where the next extreme hailstorm might be. We can only be sure of one thing: Hail is not going away, no matter how you classify it.