Condensation occurs when water vapour held in the air comes into contact with surfaces colder than the air surrounding them. This primarily affects windows and externally facing walls during seasons of colder weather, as these are normally the coldest surfaces in the house. In a nutshell, the amount of water vapour in the air is described as humidity level. When the property is subject to restricted ventilation, the humidity levels rise significantly to a point where the water vapour more readily condenses on these colder surfaces forming droplets. Over time, these droplets start to saturate surfaces such as walls which become ideal conditions for the growth of moulds and if prolonged condensation is left untreated to windows with a timber frame, can cause rotting of these timbers. Typical symptoms include droplets forming on the inside of windows and the formation of dark spots of mould on walls and ceilings especially in corner areas where air circulation is at its lowest.