Glossary
Hail resistance class (HW3/HW4)
Also known as: Hagelschutzklasse, Hagelwiderstandsklasse, HW3, HW4, Hail resistance, Hail class
The Hagelschutzklasse (hail resistance class, HW) states which hailstone a component of the building envelope withstands without damage; the number corresponds to the hailstone diameter in centimetres, so HW3 means 3 cm and HW4 means 4 cm. For solar modules, SIA 261/1 and the VKF hail register treat HW3 as the baseline; in designated hail regions, Swissolar fact sheet 17 recommends HW4. No cantonal legal requirement exists for PV modules.
The hail resistance class comes from the hail register of the Association of Cantonal Fire Insurers (VKF), which rates building components by tested hail resistance. The SIA standard 261/1 adopts this rating for the design of the building envelope. In the test procedure, solar modules are shot with ice balls of the respective diameter; the class appears in the manufacturer’s test certificate.
The bar is rising. Storm damage at AXA Switzerland stood at CHF 292 million in 2021 and CHF 239 million in 2023 (AXA, June 2025), and the climate research network NCCS expects rarer but more violent hailstorms with larger stones for Switzerland. Insurers, planners and building owners therefore increasingly demand HW3 as the standard; in exposed regions, HW4 is the economically safe choice (Swissolar fact sheet 17).
For existing systems with older modules, the hail resistance class is an argument for repowering; for new systems, it is a criterion in module selection. What to check after a hail event and what a maintenance regime looks like is covered in the article PV system maintenance: hail, soiling and system performance.