Condensation accounts for 70% of reported domestic damp and is undoubtedly a contributing cause of of damage to walls and furniture.
Condensation can commonly be attributed to a lack of balance between heating and ventilation, resulting in a rise in relative humidity. Air can hold more water vapour when warm than cold. As warm air is cooled, such as when the heating is switched off at night, it will deposit the water that it can no longer retain as condensation on a cold surface. A similar effect can be demonstrated by breathing onto a mirror or other cool surface.