Damp in buildings is caused by moisture working its way through the brickwork and masonry of a building. It can become a serious problem if the moisture penetrates vulnerable finishes or materials, particularly if it occurs in an occupied area of a building. This can decay brickwork and masonry, and can cause bubbling and discolouration of paint and wallpapers.

The most common method of moisture entering the walls of a buildings is from defective ground and surface drainage. To a certain degree, this is present in every building in the UK due to changing ground levels and day to day drainage defects. Another large problem is people using concrete and other solid finishes around the home, without considering the drainage slopes. Otherwise, drainage or plumbing leaks may contribute to moisture and dampness.

Moisture within buildings can lead to a number of issues:

• Materials, particularly organic materials such as wood, may be affected.
• Decay organisms such as mould could potentially grow, aided by the dampness.
• In very damp conditions, some organic materials can lose their structural strength. This is a particular risk with walls made from cob (earth).
• Moulds may grow on fibrous materials such as wallpaper and carpets. This is not just aesthetically damaging, it can also become a health hazard to occupants.
• The deposition of soluble salts can cause aesthetic and structural damage upon the evaporation of moisture.

In most cases, a professional will be needed to work out the primary source of the dampness in your home, so that the most effective solution to treating the problem may be found. The most common measures are:

• The creation or provision of suitable moisture sinks to dissipate the moisture at its source without causing problems to the structure or its occupants. Alternatively, the repair of defective moisture sinks may be undertaken.
• The introduction of physical barriers using damp-proof membranes or other materials to form a damp-proof course. Chemicals may also be used to form a 'hydrophobic' (water repellent) chemical damp-proof course.
• The isolation of vulnerable materials such as timber and interior finishes from damp fabric.

Today, most new houses are built with a damp-proof course of rubber sealant. In many houses, this is just about visible about a foot from ground level. Additionally, almost all new homes are built with cavity walls, which allows the dissipation of dampness in walls through ventilation. Many older homes in damp areas were built with cellars, or sub-floor cavities in order to aid the dissipation of dampness from the home.