Battered vehicles, perforated shutters, broken window panes: a hailstorm can leave a trail of destruction in its wake. The in-house test lab at TÜV Rheinland in Cologne simulates this ‘bombardment’ of various surfaces – and whether they can stand up to even the heaviest hailstorms.

Hailstone damage: insurers are changing the fine print

So, what do you have in the freezer? Well, our team at TÜV Rheinland has got a set of standardised hailstones on ice. What sounds silly is actually a serious safety issue that affects each and every one of us. Just imagine if hail were to damage roofing tiles or smash an attic window: first it would be very cold – and then very costly. Indeed, some insurers are now stipulating that the structural and other materials that are used must be able to stand up to these small – and occasionally considerably larger – lumps of ice.

Switzerland even maintains a ‘Hail Registry’. This not only classifies hail into various ‘stone grades’ but also lists products tested against hail damage. Germany’s neighbour Austria has adopted a similar approach. In addition, both countries also produce hail maps that illustrate the probability distribution of hail events at various levels of resolution. By consulting these maps, we can easily see that hail phenomena featuring large hailstones are less likely around Lake Geneva than in the mountainous canton of Bern. In Germany, recommendations are made by the German Insurance Association (GDV).

Diameters up to 6.5 cm

It’s possible that a similar setup is coming to Germany. The Earth System Knowledge Platform (ESKP) has also produced a hail map, which is based on statistics from around 3,000 hail events that occurred over a seven-year period. Even a Wikipedia search turns up a couple of similar articles: disastrous hailstorms in Reutlingen and Munich. The collateral damage is enormous and climate change is real. In its 2020 Natural Disasters Report, the GDV writes: “Alongside thousands of vehicles, buildings are also affected: window panes collapse under the weight of the hail, … with hailstones from some events measuring up to 6.5 centimetres in diameter.” By way of comparison, a golf ball measures 42.67 mm across.


A compressed-air hailstone cannon

So what does all of this have to do with TÜV Rheinland? In our solar lab in Cologne, tucked away on one side, there’s a windowless room with a massive safety door. Inside is a support frame, which can be used to mount solar modules, shutters, cladding insulation, sky domes, vehicle hoods and other objects. Positioned opposite this frame is a compressed-air launcher tube, similar to those used in tennis training. This one shoots out balls of rock-hard ice, however.

Hagelschaden Testlabor

The cannon features interchangeable bores for firing ‘hailstones’ with diameters between 20 and 50 mm, depending on testing requirements. Once the machine is loaded, the test object is blasted with ice.

These objects can also be roof sections from caravans or similar kinds of holiday homes – pretty much anything that is exposed to wind and weather during its life. And it’s good to know these coverings won’t be turned into Swiss cheese by the next hailstorm.

A standard for resisting hail

Officially, five hail resistance classes (RCs) have been defined, from RC 1 (very low resistance) to RC 5 (very high resistance). If a skylight can withstand a standardised hailstone weighing 56.9 grams striking its surface at a speed of 30.8 m/second, for example, then this skylight is categorised as an RC 5 product. Our accredited lab fires off the hailstone ‘rounds’ and then assesses the damage. Our technicians have been testing the hail resistance of solar modules for more than 20 years. Over the last six years or so they have been working closely with the Swiss Federation of Cantonal Building Insurers (VKG). Our team was also invited to participate in an extensive ‘round robin test’ that was organised by the VKG. The results from our lab clearly impressed our neighbours in Switzerland, who duly granted us permission to conduct testing according to their exacting standards.


Policyholders should check their contract for hail exclusion clauses! This can save you a lot of money, stress and paperwork. And a tip for manufacturers: while hail resistance testing is not required by law, it’s a useful way to promote your products. At the end of the day, however, it’s all about safety. And that is exactly what we do at TÜV Rheinland.


To date, we’ve only been testing brand-new materials. But it would certainly be interesting to set up a project that tests hail resistance after 20 or 30 years. Are older shutters or cladding systems that have been exposed to the elements for years on end just as resistant as new ones? I’ve not found any research in this field. Are you interested in finding out more? Our lab is located in Cologne.





Every day she is fascinated anew by her diverse job and her expert colleagues. She is eager to learn and tries to incorporate innovations into her everyday life. She loves the balancing act between work and family, enjoys being on or near the water and reads even more than she writes.

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