Rising damp can occur in both internal and external walls. Moistures draws up, by means of capillary action, from the ground the walls are in contact with. Typically rising damp will travel up a wall between 1.20 and 1.50 metres above external ground level.
There are several reasons why rising damp may appear within a structure. It may be that the building pre-dates a time when damp proof courses were ever installed. It may be the case that an existing damp proof course has failed or perhaps was poorly installed.
A common first indication that a structure may be suffering from rising damp is the deterioration of internal finishes, such as plaster beginning to de-bond or wallpaper starting to peel off. The salts that are drawn up with the moisture through the capillary network can have a devastating impact, both aesthetically and structurally, on the wall that is subject to the rising damp. Not only this, rising damp can also pose serious health hazards to those exposed to it, particularly if mould develops, such as allergic reactions and respiratory problems.