Rising damp is not as common as some contractors would have you believe. This problem typically occurs with movement of water in the foundations of the building that extend beneath the ground water table. Moisture can rise up through the structure via a process that is referred to as ‘Capillarity’. The factors that effect the amount of moisture absorbed and the height that is impacted can be categorised into three groups.
The capacity of the wall material that the rising damp effects.
The level of water on the ground.
The volume of moisture that evaporates.
During the process, water rises upwards, through the wall and eventually makes contact with the ‘physical barrier known as the damp proof course (DPC) Most modern buildings are designed to include a DPC (damp proof course) which is a layer of Bitumen, plastic or slate that is built into the external walls slightly above the ground level. The damp proof course stops the damp rising within the wall – so if a DPC is not present, the water will continuously seep upwards to an average maximum of 1.5 metres (however, this can sometimes be exceeded).
A typical scenario where rising damp becomes a problem is when the the existing damp proof course is bridged due to high external ground levels or even where the internal wall plaster is plastered to the floor, DPC, Damp proof courses have been mandatory for building regulations for over a century … but unfortunately, that does not mean that every property constructed since this time contains one! Old buildings (such as properties with brick or solid stone external walls) will not necessarily have a damp proof course, these types of structures are obviously at a much higher risk of rising damp. If you suspect that this may be a problem, a full, professional inspection would need to be carried out to determine the cause of the dampness.