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What is condensation?
Condensation is the humid, foggy precipitation of water on objects such as bottles, mirrors, tiles, or windowpanes. It is formed when humid hot air meets a cold surface. Hot air can bind significantly more water than cold air. If hot air cools off (e.g. on a windowpane), the superfluous water contained in the air condenses on the object.
Condensation on windows
Windows are always the coldest surfaces in the room. Therefore, condensation forms on panes first. There is no such thing as a window with the same surface temperature as a brick wall. To that end, several thermo panes would have to be built in the same sash - a construction, which is not feasible.
Due to their position, roof windows are particularly exposed to snow, hail, rain, and storm. Thus, they are cooled off more than vertical windows, and again - condensation will be formed on the roof window before anywhere else.
30 years ago vapour barriers, intermediate rafter insulation, and thermal glazing were concepts almost unknown. Not until the energy crisis in the seventies, did people become more energy conscious, largely because of the increase in oil prices.
Before that time, the price of heating had been favourable, and dwellings were still not airtight rooms. The wind whistled under the roof; windows clattered, and non-watertight joints provided permanent natural ventilation in the house. Thus, dry air streamed in from the outside and the humid air in the room escaped to the outside. On top of that, the furnishings (flooring, furniture, wall paintings and wallpaper) consisted of highly absorbent, natural materials, which were good at binding atmospheric humidity.
The air in the rooms was therefore much drier than today and normally water did not condense on the windowpanes. Today, there is thermal glazing, insulation layers and tight joints designed to keep the rooms warm, while also, keeping the moisture locked inside our living rooms. Therefore, homeowners have to provide sufficient ventilation and correct room temperature in order to regulate the atmospheric humidity in their homes.
Have you ever considered how much humidity will be released to the air of the room in one day? Besides the room and potted plants; cooking, showering, bathing and clothes' washing see to it that the air will well be enriched with humidity.
Added to this is the breathing and perspiration of people. In the long run, the atmospheric humidity may damage material and health, and cause mould to develop. Regular ventilation is the only way to effectively prevent that from happening.
In order to avoid condensation, the room temperature should be kept as constant as possible. A constant room temperature of 21°C and a relative atmospheric humidity of about 40% in the rooms provide healthy living conditions. Moreover this combination hardly ever causes any problems with condensation on the windowpanes.
Limiting the development of aqueous vapour
Treating water stains on the frames
All windows should be coated with a suitable water resistant barrier, which makes them humidity proof to a high degree. In spite of this, over a period, stains may appear caused by condensation. These discolouring do not actually harm the window and can easily be removed:
When condensation forms on the panes of your windows, consider it a warning signal, telling you that you should ventilate at once.
Correct ventilation is achieved by opening your windows completely 3 - 4 time a day for 5 minutes, at best, creating a draught. In this short period of time, you will ensure that neither furniture nor walls will cool down during ventilation. By doing it this way, you do not only replace the humid indoor air by the dry outdoor air - you also save heating costs. If the windows are open constantly, or the ventilation flap is never closed, this will cause unnecessary loss of energy in the heating season.
When your central heating unit is provided with automatic lowering of the temperature during the night, you should ventilate before the heating temperature is lowered. In this way, you will avoid that the warm room air condensing when it is cooled down during the night.
Ventilating correctly is the most efficient way of preventing condensation water from forming on your panes.