Given the apparent simplicity of the term, this window property seems the easiest to explain. Some readers may already know that windows are not simply divided into watertight and non-watertight. For exposed windows, there are 10 watertightness classes, from 1A to 9A and the special class Exxxx, where xxxx indicates a pressure above 600 Pa.
Window and door watertightness in the European Union is defined by EN 1027. This standard defines water penetration through fully installed windows and doors, fitted according to the manufacturer’s specifications. In principle, the installed finished product is tested by spraying the window and frame surface under a specified pressure, then measuring the pressure at which water penetrates during a test period of 5+n minutes.
The following table shows the classes assigned to windows and doors based on the pressure they withstand. I have also added the wind speed with rain needed to generate that pressure. Strong wind can, however, deform window or door frames, so this table should also be considered alongside wind resistance.
