The condensation which forms inside buildings is caused by the presence of moisture. Usually it is a phenomenon that occurs in the winter period and it is linked to the appearance of moisture stains, mould as well as deteriorations of the plastering. Condensation forms on the internal surfaces of a house due to two factors: the high concentration of steam or the low temperature of the surfaces in contact with the air. The water is deposited on the surface due to the transformation of air from the gaseous state into the liquid; this occurs when the humidity of the environment exceeds a certain threshold or when the surface temperature drops below a certain level. The very high level of humidity in the air, for example, is created from having a very hot shower, or after having cooked for a very long time, or where lots of people have been present in a room for a long time. In the example of the shower, there is so much vapour in the air that the condensation is deposited on mirrors and tiles, whereas in the case of a cold can or bottle just out of the refrigerator, the air in contact with these cold surfaces is instantly transformed and becomes a liquid.
Since the windows surfaces are “colder”, despite the low-emissivity of the glass which is ever more efficient and insulating, one has not yet reached the very low Thermal Transmittance, which can be a wall; in fact, the walls reach up to 0.26 W / mqK while with the windows they can also reach values of 0.90 W / mqK. These values, however, are insufficient to prevent the phenomenon.