The one major cause of mould anywhere in the house is moisture. Without sufficient about of moisture mould cannot grow. So when we discuss causes of moulds in houses we really need to talk about causes of dampness and water in the cause which subsequently cause mould. There are four ways how moisture can get into the buildings and these are rising moisture, Penetrating moisture, Condensation and Leaking services.
Rising moisture consist of the moisture from the ground rising through porous wall construction by means of capillary action. The classic sign is a damp line and damage to surface finishing reaching to about 1m height form the ground
Penetrating moisture consists of rain and usually flood penetrating the interior of the house from the outside, usually with the help of wind and gravity. There are many parts of the building envelope that can deteriorates and allow water to penetrate into the building.
Condensation is usually the most complicated form of dampness sometimes occurring between the leaf of the wall construction, between layers of decorative materials and on the internal surfaces of walls or items. It occurs most often in winter when the houses not ventilated as much as in summer.
The fourth way of water ingress into the building is via leaking services. Leaking external pipes, drainage gutters, internal house pipe work and a multitude of appliances are all potential sources of water.