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Windows resistant to strong winds!

Polish climate is characterised by changeable weather conditions. Therefore, we often experience sudden weather breakdowns, big temperature fluctuations, as well as strong winds or even gale lashing the country. As a result of climate changes, atmospheric phenomena, such as whirlwinds, are increasingly stronger.

The intensifying climate changes take place mostly at the turn of winter and spring. This is when strong and unexpected atmospheric phenomena occur, connected with remodeling of the afflux of sunrays, which means that the Earth starts to heat up and the Atlantic is still warm. Therefore, the weather changes, which are difficult to predict, occur before a relative balance is achieved on the rim between the continent and the ocean.

Unfortunately, weather forecasts are rather bleak. As meteorologist claim, violent storms and gale-force winds will be more and more common due to climate changes. Therefore, it is worth checking the quality of our windows, and, before buying new windows, one should analyze the parameters that really determine if the woodwork will be resistant to wind pressure and if it will be able to protect us against infiltration of rainwater.

Resistance to wind load and water resistance are essential criteria that determine window quality. They are extremely important for those who occupy high floors and for owners of houses that are located in open country and at the seaside.


Wind resistance

Strong wind may cause permanent window deformation through frame deflection even by a few millimeters. This type of activity results in permanent unsealing. To ensure comfort and protection against negative atmospheric influence, it is necessary to invest in high-quality windows characterized by high rigidity.

Resistance to wind load, or window rigidity, determines the class. The resistance index regarding wind load indicates the speed of wind when the maximum acceptable deflection of the most deformed window element will take place. It must not exceed 1/300 of the length of the specific element. It is important to select the parameter depending on the wind intensity in the location, since windows in a multi-storey building will have different wind resistance than a single-storey house, which is determined by the physics of the construction. 

 „Testing the class of window resistance to wind is performer in laboratory research. The study consists of application of a specific series of positive and negative test pressure, when measures and controls are carried out, in order to evaluate the relative front deflection and the resistance to damage resulting from wind load.’’ - says Arkadiusz Listwon, DRUTEX S.A.

Front deflection is the maximum front displacement of the sash frame element minus half of the total sum of front displacements at each end of the element.

Front displacement is the displacement of a point of the sash frame element measured perpendicularly to the element.


The window is classified according to two values:

1. o wind load, such as:


Pressure [Pa]


Not tested













Where xxxx stands for the pressure value – but as a rule, tests are not carried out with such extreme pressure.

2. relative front deflection, i.e.:


Relative front deflection


< 1/150


< 1/200


< 1/300


Resistance to wind load is marked, basing on such tests, by symbols from A-1 (lowest rigidity) to C-5 (highest). Considering our climate conditions, an average residential building needs a window of class B-3/B-4 resistance to wind load, in extreme cases exposed to strong winds, i.e. at heights or in open country - C-3/C-4. It means that wind pressing with the strength of 1200/1600 Pa (i.e. 158-184 km/h) will lead to frame deflection not higher than 1/300 of the length.



The window with the highest resistance to wind, classified with C-6 symbol, means that the wind blowing at 205 km/h speed will deform the frame by 1/300 of its length. Window with the lowest resistance to wind in A-1 class means that wind blowing at 90 km/h speed will lead to the maximum frame deflection, i.e. 1/150 of its length.

Having achieved the specific class it is necessary to check if the window will resist the repetitive conditions. Therefore, during the test we carry out 50 cycles of pressure and suction (positive and negative pressure, and the pressure value is half of the value of the class that we achieved).

It is also vital that an important resistance test for the window, especially for the fittings, is so called safety test. A sample undergoes one cycle of negative and positive pressure. Pressure value depends on the class that we achieved in the test. It is multiplied by 1.5. The test allows to determine the quality and rigidity of the fittings, thereby, the window resistance to wind load strength.

„Window testing is a requirement, and the producer has to attach to every window the product card with information regarding the tested parameters and the classes. That is why before you buy a window you should check the parameters that the product guarantees, and therefore – the safety level it offers. Three parameters are highly important in this case: resistance to wind and the relevant water resistance and air permeability. Facing the frequent weather changes, it is worth remembering that window parameters may determine the usage comfort and our satisfaction.’’ – advises Arkadiusz Listwon from DRUTEX S.A.


Modern windows are characterized by technological advancement. Cutting-edge solutions often determine their high quality. We may find the woodwork that will perfectly match our needs and preferences regarding shapes, colors and window sizes. However, we must not forget that the crucial parameters are: resistance to wind load and water tightness. Therefore, one needs to check and ask, because such knowledge gives us the certainty that we made the right choice of the window. We need to ask the producer for certificates, attestations, and technical approvals. It is important to trust reliable partners, companies with traditions and history, whose credibility is confirmed by perennial experience in the industry. 

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