Damp walls in buildings can generally be divided into 3 main catagories, each caused by a different phenominum. The categories are rising damp, penetrating damp and condensation.

Rising damp is the upward movement of ground water through the pores of a permeable masonry wall via a process called capillarity. Capillarity is the same process that enables the movement of water from tree roots to tree tops via intricately stacked hollow cells despite the counteractive force of gravity

Rising damp typically occurs if the built-in damp proof course is bridged, for example by a change in ground level, or if the damp course is damaged, for example by a structural alteration or a chemical reaction. In such cases rising damp may become a problem if it is likely to affect vulnerable materials or finishes that are in contact with the wall. For example if the damp has potential to rot joists, skirting boards or the bottom of door frames or if it causes wall plaster or wall coverings to deteriorate or become damp stained.

Modern damp proofing products include effective, environmentally friendly and easy to use damp proofing creams that can be used by a general builder or a competent DIY enthusiast to line the pores along a stretch of masonry wall with a silicone resin water repellent to form a new DPC.

Penetrating damp occurs where water soaks into the living accomodation of the building, either above or below ground level. Above ground level, penetrating damp is usually due to one or more building maintenance defects. An example of this could be a leaking rainwater pipe which, combined with delapidated pointing, frost damaged bricks or faulty joints between window and walls, has allowed damp to soak completely through the wall.

Fortunately once the building defect is rectified the likelihood of further penetrating damp is minimised. Effective and breathable water repellent emulsions, sprayed onto external masonry can help to protect facades and guard against damp penetration.

In below ground situations, exterior basement walls are typically subjected to a constantly damp environment. Protection to the internal srfaces and control of water ingress can be afforded by structural waterproof tanking or by the provision of the dimpled waterproof membrane systems that have been developed to provide a solution to damp walls and floors for basement and cellar renovations.

Damp mould on walls and celings can be caused by the air held inside a building, which often incorporates high moisture content due to cooking, bathing, drying clothes etc. As the temperature of humid air drops, its capacity to retain its water vapour content reduces and once a dew point is reached, the condensate is deposited onto surfaces that are cooler than the moisture laden air.

Condensation damp is immediately obvious on non-porous surfaces such as glass and ceramics but is, initially, less noticeable on porous surfaces such as plasterboards, wall plaster and timber, which may simply absorb the damp and encourage black mould growth.

To manage humidity and control condensation effectively:

• homes are adequately heated - warm air has higher water carrying capacity than cool air.
• walls are insulated - a warm wall is less likely to attract condensate
• ventilation is increased - force moisture laden air out of the home to lower the humidity and dew point

Painted surfaces can be treated with fungicidal washes to remove moulds and fungi. Anti-mould paints are available, though it is often more cost effective to supplement standard emulsions with fungicidal additives to protect against further damp mould growth

Heat recovery ventilation units and positive ventilation systems minimise condensation potential and are inexpensive to run.