After the Storm: Hail Damage to Metal Roofs

Severe weather events, including heavy rainfall, high-speed winds, large hail, and tornadoes, can cause significant property damage. With about 70% of these storms occurring between March and June in the Central and Southeast United States, it is important to promptly inspect any property damage and determine its severity. While metal roofs are generally more resistant to hail than shingle roofs, the severity of damage depends on several factors such as the size and density of the hailstones, the thickness and type of roof materials, and the quality of the roof installation. Hail can cause dents, distort panels, or damage side laps, seams, or fasteners, compromising the water-shedding capability of the roof and potentially leading to water intrusion or leakage.

Many metal roof panels are designed to withstand small scratches and hail dents depending on the type of protective coating, metal type, panel dimensions, roof slope, and underlying structure (Figure 1). It has been shown through industry research and testing that dents from hail impacts that do not disengage panels or fasteners or disrupt protective surface coatings do not diminish the roof’s ability to shed water or reduce its expected useful service life. Dents from hail are common in metal roofs. Testing and experience have shown that penetrations in steel roof panels can occur with hail starting around 2.5 inches. It is possible for the water-shedding capability to be compromised if the hail is large enough to damage side laps, seams, or fasteners. If panel side laps or seams are distorted by hail, they may be subject to water intrusion (Figure 2 - Figure 3). Exposed fasteners can be damaged or become disengaged if impacted by large enough hail. Any penetration in the panel, disengaged fastener, or other openings created by hail can compromise the water-shedding capability of the roof.

A prominent protective coating within the construction industry is Galvalume which combines three of the most important and high-performing metals used in roofing today – steel, aluminum, and zinc – making it especially resistant to rust and corrosion. Due to the zinc concentration, the coating also has self-healing characteristics that help prevent red rust at any cut or exposed edges and reduce the overall risk of failure in the roof.

Due to the advancements in protective coatings like Galvalume, it is more important than ever to know what to look for when inspecting a metal roof for hail damage. Even if there are visible dents from hail, it does not necessarily mean the roofing system is compromised, especially when a cosmetic damage endorsement is involved. In addition to a visual examination of the roof structure, inspections should include laboratory testing by qualified materials experts or engineers to determine if any protective coating has been compromised.

The influence of hailstone impacts on the long-term performance of formed steel roof panels with zinc-rich coatings such as Galvalume has been the subject of numerous insurance claims. With the increasing prevalence of policies with cosmetic damage exclusions, those who investigate these claims can no longer only use visual inspection to determine whether a metal roof has been damaged by hail. In the past, observation of hail dents translated into direct physical damage. Now that so much of what was previously considered direct physical damage is now only cosmetic marring, investigation of these types of claims has become more in-depth and nuanced.

To investigate another part of these claims, that a hail stone may compromise the factory coating such as Galvalume, we must bring in a materials expert to perform analysis using a Scanning Electron Microscope (SEM) with Energy Dispersive Xray Spectroscopy (EDS). SEM examination allows for higher magnification and depth of field imaging compared to light optical microscopy (Figure 4 - Figure 5). EDS is a semi-quantitative technique that analyzes X-rays emitted from selected regions of the sample surface to determine the relative concentrations of chemical elements present within the analyzed regions.

In short, it can detect whether the protective coating has been compromised and if the underlying steel has been exposed (Figure 6).

To further characterize the condition of the protective coating, metallographic examination is often employed. This technique permits direct examination of a cross-section through the coating and underlying steel substrate within the indent, albeit at a single plane, for any thickness loss, damage, and/or corrosive attack (Figure 7 - Figure 9).

A recent study by Ron Dutton and Robert Haddock[1] presented at the 2023 International Institute of Building Enclosure Consultants (IIBEC) International Convention and Trade Show looked at the effect of microfractures in the factory coating of metal roof panels as well as the effect of water ponding in hail divots on the service life of the roof. What they found was that scratches do not affect the service life and microfractures in the coating are rare. They also found water evaporates faster from a hail dent than other parts of the roof.

Studies like Dutton and Haddock’s and the capabilities of modern protective roof coating serve to further exemplify the need for materials experts or engineers to be involved when inspecting a roof for hail damage. Qualified experts employing tools and techniques like SEMs and EDS can more definitively determine whether a roof has received structural or cosmetic damage and more accurately advise on what level of repairs are required. ?

[1] Dutton, Ron, and Robert Haddock. 2023. “Oh Hail! Metal Roofs, Hail Impact, and Long-Term Performance.” Published in the Proceedings of 2023 IIBEC International Convention and Trade Show, March 3-6, 2023, in Orlando, FL: International Institute of Building Enclosure Consultants.

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