Moisture is always present in buildings, and certain levels of natural moisture are necessary to keep the building fabric in a stable condition. The moisture content varies widely with the type of material, ranging from 1 per cent for plaster to 20 per cent for timber.

The term ‘dampness’ is reserved for conditions under which moisture is present in quantities, perceptible to the eye or to the touch, which can cause deterioration to the decoration and fabric of the building. '

Preventing or curing dampness is still the major maintenance problem, however it is also important to remember that an essential characteristic of a traditional building is its permeability to water vapour, and its ability to ‘breathe’; the introduction of unnecessary vapour barriers and damp-proof courses may do more harm than good.

The inspection should be systematic, beginning perhaps in the roof space and going down through all the rooms to the basement, followed by an external examination. Touch, sight and smell are often the best aids to diagnosis.

An inspection should identify the cause or causes, which may be far from obvious. It is advisable to employ an architect or a building defects consultant, who should take the following factors into account:

1. Extent : Is the damp widespread or does it occur in isolated patches?
2. Pattern :Does the damp relate to certain features, such as window openings, chimneys, gutters, etc.?
3. Period : Does the dampness occur only after long spells of rain, when the air is humid, or after a rise in temperature? Is it persistent or spasmodic? And is it related to previous building repairs?
4. Use :Does the dampness coincide with a change of use of the house or a change in the lifestyle of the occupants?

If the causes are not clear, then seek expert advice. A good moisture meter may help the initial investigation, bearing in mind that a surface reading is not always a reliable guide to the source of damp. In fact, such readings are known to have led to a few unnecessary expensive repairs. More reliable information is obtained by weighing samples of material drilled from the wall, or by using a carbide moisture meter. These techniques require skill and special equipment, and there are firms who will obtain and analyse samples.

The causes of dampness can be divided into four categories:

• Water penetration (through walls or roof)
• Condensation (including Chimney Breast Dampness)
• Rising damp
• Other causes of damp