Water can rise up through most materials used for building houses, such as brick, concrete and stone. (In scientific terms, this is cause by capillary action.)
To prevent this happening, a damp proof course (DPC) is inserted in any walls which rest on foundations laid in the ground. This is intended to provide an impervious barrier to water. The DPC is installed as a horizontal layer between two courses of brickwork. It should be a short distance above ground level so that ground water cannot bridge the DPC.
In modern properties the DPC is usually a thick plastic strip, but other materials which have been used include Bituminous Felt, slate, and lead sheet. The Romans used oyster shells for this purpose.
Cavity Walls require a DPC in each leaf of the wall.
Potential problems with DPCs
- Failure of the DPC – this might be caused by damage during installation, or cracking of rigid DPC materials, such as slate, caused by settlement or subsidence.
- Bridging of the DPC – this often happens when earth or rubble is heaped up against an outside wall, or a patio or paved area is built up above the level of the DPC. It can also occur when external rendering is applied across the DPC. When this happens moisture can rise into the brickwork above the DPC.
The surveyor will report on any indications of problems with the DPC, and advise whether a further specialist survey is required or if remedial work is necessary.