What causes condensation?
Air inside a building contains a certain amount of water vapour. This increases dramatically the larger the family, (we all breath out moisture) when kettles are boiled, baths are run and clothes are dried indoors.

Warm air is able to hold more moisture vapour than cool air. When the hot damp air circulates it will eventually come into contact with cooler areas (e.g Windows, doors, walls)

Once the air cools, it can no longer hold as much moisture and this is deposited on the colder surface. If condensation regularily forms in particular areas, black mould usually forms.

Although the black mould can cause an unhealthy environment, it is also a tell tale. If you have mould then the dampness it is not being cause by a defective damp proof course. (i.e Rising dampness.) Black mould is caused by condensation.

This is discussed in greater depth in my book Domestic Building Surveys

ISBN: 9780419178002

Ways to prevent condensation occurring.

Although most people don’t like losing heat, getting rid of the surplus moisture prevents it building up in the air.

Simply opening a window after having a bath or shower can get rid of unwanted water vapour.

Fitting suitable extract fans and controllers in bathrooms and kitchens will also reduce vapour in the air.

Many loft spaces do not have ventilation tiles fitted. Once again, the additional ventilation will help to reduce a build up of vapour being held in warm air.

Make sure that tumbler dryers are vented properly.

Consider installing cavity wall insulation if your property does not have cavity insulation. Not only does the insulation help to prevent heat loss it also helps to keep the inside of the external walls warmer. A warm wall is unlikely to be affected by condensation.