Window waterproof

Watertightness of windows.

High-quality windows not only provide the right amount of light in the interior, but also protect them from water ingress. The water tightness of the structure is informed by the water resistance class of the windows. It is determined during tests simulating real-world weather conditions.

Window waterproof test

To assess the extent to which the windows are leaking on rainwater, it is necessary to carry out appropriate tests. The design tested (window, door, terrace or HST)shall be placed in such a way that it forms one of the walls of the test chamber. Importantly, the outer side of the window is facing the center of the chamber. In the chamber it is possible to make pressure changes, as well as simulate the actual precipitation by using special sprinkler nozzles. Recommendations for the placement of nozzles and the amount of water administered are contained in the test standard PN-EN 1027.

Window waterproof class – how to determine

Testing the window for water resistance involves ingening the structure with water and checking for liquid ingress outside. Initially, the window is poured with water for 15 minutes, with a test pressure of 0 Pa. Then the pressure value is increased every 5 minutes. If the structure remains tight for 5 minutes at increased pressure, the test pressure value is increased again. The amendments shall be made in accordance with the following table:

Waterproof classTest pressure q [Pa]Corresponding wind speed v [km/h] Test time
T. [min]

By increasing the pressure value, the wind is increasingly stronger and the least favorable weather conditions are checked, where the window still remains tight to rainwater. When water penetrates the window, it obtains the water resistance class that corresponds to the highest pressure without leakage.


The leak occurred when the test pressure value was 750 Pa. In this case, the window receives a waterproof class corresponding to a pressure of 600 Pa (9 A).

The waterproof class indicates that the rainwater window is tight.

What designs are well watertight?

The highest waterproof classes are achieved by structures where the threshold is made of a frame profile (the same frame around). Such windows are described in water resistance class E1050 – therefore they remain airtight in wind, which blows at a speed of almost 150 km/h. Large terrace structures with a low threshold or a lift and sliding door(Patio HST)tend to achieve lower values. Although they use a very complex sealing system, the lowered threshold contributes to a slightly lower waterproofing class.

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