Most of us are confidently aware of the problem with the excessive moisture on the windows. This negative natural process occurs mostly in the winter, but also when it cools down rapidly during other seasons. As the air, depending on the temperature, is able to absorb only a certain amount of water vapor, this excess must “get away”, which practically means precipitation of water on the coldest surfaces. Although water is precipitated on various surfaces, it is most visible on the windows. Where do you get water vapor in the interior of your apartment? Before we answer this question, we must realize that there are the two basic phases of the existence of the building:

  • Construction stage
  • Usage stage

Construction stage:  the main source of humidity is the construction itself – young construction = fresh plaster, masonry, cast concrete floor, etc. This stage is specific for the construction in terms of evaporation of excess water from the interior of the building. If wooden windows are already installed in the building, effective ventilation is necessary, especially for two reasons:

  • Windows protection
  • Protection of the construction itself

In case of a high humidity in the room, this excess water gets into the wood and increases its moisture to a level that damages it (peeling, mould, fungi,) and aesthetically degrades (water “bubbles” under the paint of the window) the wood. If the moisture on the glass is optically visible, these spaces must be effectively ventilated by fully opening the windows for more than 45 minutes. Thus, moisture removal is ensured and the excessive moisture disappears. The construction itself also suffers from the insufficient moisture drainage because there is no rapid drying of the construction structures from a technological point of view. Achieving a balance in terms of humidity may last for several years.

Usage stage: the most typical sources of moisture in this stage are:

  • Bathing
  • Dish washing
  • Breathing of human beings, animals and plants,
  • Cooking
  • air moisturizers
  • laundry drying,
  • aquariums, terrariums, etc.

We must realize that the most common mistake leading into excessive moisture on the windows is the insufficient and incorrect ventilation. The persistent prejudices that we are extinguishing precious heat are only partially true, and this is especially true in the case of the incorrect ventilation. Ventilation should be intense and short; we will achieve it by opening the window wings fully (not tilted) for 5-20 minutes. We try to open the windows that are opposite each other in order to reach a sufficiently intense air flow.

We should ventilate at least twice a day before bedtime and in the morning after awakening. Tilting the window is an effective ventilation tool predominantly in “summer” months when it is possible to ventilate the premises of the house for a whole day. At that time the fresh air is supplied to the interior and the rooms themselves are perfectly ventilated.

Modern windows have a high sealing capability, but the manufacturers themselves try to solve the excessive moisture creation on the windows by different structural modifications, for example by the means of micro ventilation, when the window is only slightly folded and its position is secured by the fitting itself.

When talking about the long-term period, the most problematic room is the bathroom. We can see the water vapor mainly on the windows and the mirror, but we have to realize that moisture is also precipitated on the walls. As walls, plasterboard and similar structures, unlike glass, absorb moisture and it is then more difficult to remove, it can cause unwanted moulds and the walls damage in case of prolonged exposure.

Another possible cause of the moisture collection on the windows may be inappropriately chosen glazing. The quality of the insulating double or triple glazing is characterized by the heat transfer coefficient U (W / m².K). The lower the coefficient value, the higher the thermal insulation capacity of the glass, the higher the internal glass surface temperature and the lower water condensation on the glass. Otherwise, the glass surface temperature is lower, as is the ambient air temperature, which means lower water solubility and condensation on the glass.

A relatively frequent phenomenon is the moisture collection on the new windows in old houses – here we come to the next possible causes of moisture collection – insufficient thermal insulation of the perimeter structures, but also inappropriate thermal insulation. The insufficient thermal insulation capacity of the perimeter structures can be solved by the thermal insulation for buildings. However, you must be careful with the thermal insulation of new buildings whose perimeter structures contain a high percentage of moisture – here we have to look for heat-insulating materials with lower diffusion resistance to keep moisture in the walls and not to redirect it to the interior.

The inappropriate placement of heating bodies can be another cause. If the heaters are under the windows, the heated air flows around the windows and reduces the risk of moisture collection. If there is, for example, an opposing wall, cooled air is flowing around the windows and condensation occurs. Increased risk is also the case with floor heating, when window panes are not heated so intensively and therefore convectors are also used on larger glazed areas. Attention is also drawn to the various obstacles that prevent or limit the flow of warm air around windows – for example, large window sills, various covers of heating bodies, etc. In this case, the solution is the ventilation holes and grilles that direct the warm air.

The interior blinds also limit air flow and are another cause of the moisture collection. The solution is the external blinds or blinds that do not prevent the flow of warm air.

Finally, we can only recommend observing the above principles and getting used to the right ventilation habits.