Damp Information
Damp Proof Course.
A damp proof course. (dpc) is simply a piece of waterproof material such as slate, or bitumen mainly used from 1875 up until 1950. Today there are various modern materials still including bitumen but also PVC, that are laid across the full width of the thickness of a wall, once it has reached the height of three or four brick courses, so that it is quite clear of the ground level, the current statute being 150mm (6”) The rest of the building is then constructed above it. This sandwiched membrane will act as a barrier to prevent any ground moisture that becomes sucked up by the footings from going any further, and that is all it is.
Properties before 1875 were not required to have damp proof courses, mainly because nobody suspected that given time dampness in the ground could work its way up into the lower walls and ground floors of the building and cause rising damp and its associated problems. However the statute for damp courses took quite a time to implement and it was still some years before building regulations compelled builders to incorporate some form of dpc in the footings of brick built properties. This is why it is still common to find buildings without any form of dpc as late as 1913. As you can imagine, if those buildings are still standing today it would be more than likely that they would have a history of rising damp problems (see fig 1). Otherwise in properties that conformed, the majority of damp proof courses were of slate, a natural mineral mined mostly from Welsh hillsides, used extensively for roof tiling because of its sedentary composition which allowed it to split easily thus making it a viable and lucrative commercial aspect for its time, and indeed millions of houses in the British Isles still remain protected from the weather under a slated roof. But even those exposed to the elements above ground often become subject to water ingress and frost, or because of their inflexibility, become damaged from fractures caused by movement of the property. Many become bridged by cement plinths that although constructed with good intentions to protect the edges and lower brickwork from rainwater splash, unfortunately, were and sometimes still are, constructed too high against the external walls so that the groundwater works its way up between the plinth and the wall by-passing the damp proof course. (dpc) Similarly with ground that has been built up, that is in contact with the external brickwork. This not only bridges the dpc but also allows water to laterally penetrate the wall which is then known as penetrating damp, but once in the wall can rise by capillary action up to a metre high. This is often visible to the internal plaster. In the case of high ground this can be remedied by lowering the soil so that it is at least 150mm below the damp proof course although by then so much water has affected the slate that it has usually become delaminated and broken down. See fig 2, fig 3, fig 4, fig 5 & fig 6. So to conclude, rising damp is where ground water permeates through the footings and lower brickwork by capillary action, (either because there is no original dpc, or the existing dpc has become defective) usually via the mortar joints. Most bricks are too dense to absorb much water except perhaps some of the Victorian reds that are much softer and the more prone to spalling. (erosion by frost damage)
