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The main causes of damp and mould

There are three main causes of damp and mould within properties. They are:

  • penetrating damp
  • rising damp
  • condensation, leading to mould growth.

Penetrating damp  

This occurs when there’s a defect with the fabric of the building or services within it, allowing water to enter the property. This could be a roof leak, disrepair to window and/or door frames or a leak from a water pipe inside the property.

Penetrating damp can usually be identified by water staining, typically yellowy brown in colour, in a particular area where the water is entering the property. The location of this staining is generally an indication of the source of the leak/water penetration.


  • damaged/misshapen plaster - plaster will blister, show signs of disintegration or signs of 'salting'
  • localised dampness
  • mould growth
  • damaged internal decoration
  • rotting floor timbers or skirting boards.


Rising damp

Rising damp is caused by the breakdown, deterioration or bridging of the damp proof course of the building. Moisture then rises up the walls to a maximum height of 1m. As with penetrating damp, it can be identified by a tide mark which can be yellowy brown or can be white and textured. This texture is caused by salts from the ground and the plaster being drawn through the wall with water.


  • damp or wet patches appearing on walls
  • salts within the flaky or bubbling plaster
  • rotten skirting boards and flooring
  • damp and musty smell
  • rusting iron and steel fasteners
  • crumbling bricks and mortar between bricks.


Condensation, leading to mould growth

This is by far the most common cause of damp and mould within properties, particularly during the winter months.

As the weather gets colder and heating is turned on, windows are generally fully closed. The average family produces around 20 pints (11.4 litres) of moisture a day in an unvented property, and this moisture will condense within the property.

This moisture can cause mould growth on walls and ceilings as well as on furniture and your possessions.

Common signs of damp inside a house

  • damp and musty smell
  • the appearance of mould or mildew on walls, floors or ceilings
  • walls, floors or ceilings that feel cold or damp
  • dark or discoloured patches on walls or plaster
  • lifting or peeling wallpaper
  • excessive condensation on windows.


Read our damp and mould leaflet.


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