A damp proof course (or DPC) is a layer built into a wall, or injected at a later date, which prevents moisture rising up the wall via capillary action. Without a damp-proof course, rising damp will move from the ground and up the wall; in most cases, this will be to a height of around 500 – 600mm above floor level. In some cases, usually where there are high concentrations of hygroscopic salts, it may rise higher up the walls and there can sometimes be a ‘tide mark’ showing the extent of visible damp. A DPC is a requirement of any new build and have been for many years now. Building Regulations suggest that a DPC may be constructed of:
“Bituminous material, polyethylene, engineering bricks, slates in cement mortar or any other material that will prevent the passage of moisture”.
From Georgian to Victorian
Georgian (1714-1837) and early Victorian properties (1837 – 1870) were not usually built with physical DPC’s. Residents were aware of the importance of ventilation and moisture reduction. Early Victorian properties tended to have solid walls and as these surfaces were cold they were prone to condensation; lack of a cavity also meant that driving rain could cause rain water penetration where the external wall surfaces are particularly porous (soft stone, or brick construction), or the external pointing is in a poor condition.
By 1875, the inclusion of a DPC became compulsory in properties being built in London. This would generally be a single, or double layer of slate built into the structural walls, at the correct position above external ground level.
Edwardian
Edwardian properties (1901 – 1910) tended to still be solid wall construction with the DPC being either bitumen, slate or sometimes with hessian used along with engineering bricks.
Slate is a very effective form of DPC, although could be cracked, or damaged over time (possibly due to structural movement in the property, which could result in areas of rising damp from the ground.
Cavity walls
From the 1920’s, properties were starting to be built with cavity walls. The wall would consist of two layers of brick, with the outer layer giving protection from the weather and the inner layer providing a dry inner wall. A DPC would be built into both the outer and inner wall and often “bridged” across the cavity. The air in that cavity helped to prevent moisture being transmitted from the outside of the property to the rooms within. Although this was an important development in construction, it did not necessarily provide a robust solution for the long term as loose mortar within the cavity could fall into the cavity, which could result in damp being transmitted from the outside wall, across the cavity, to the inner wall.
Ventilation
Another important development within this period was the introduction of air bricks to help ventilate properties. These were usually clay bricks, which can often be seen installed in walls at high level, which provide passive ventilation and natural air movement to help reduce condensation and related problems.
Between the 1920s and 1980s the most common types of DPC’s being built into walls, were bitumen and felt based, with polypropylene (PP) DPC’s being introduced in the 1960’s – 1970s.
Damp proof course injection
Where an older property requires remedial work to overcome rising damp in walls, the most common solution is a chemical injected DPC into the existing wall, at the appropriate height. Preservation Treatments use a DPC cream, which has been rigorously tested for the treatment of rising damp. It is a solvent-free, high strength formulation which has been proven to work in a wide range of conditions, including 95% saturation, low porosity, salt water and lime mortar.
Suspect damp?
If you believe that rising damp is affecting your property and would like one of our team of experts to visit, to give you advise, or would like to talk to one of our qualified Surveyors regarding an appropriate solution, then please contact us on:
Tel: 01276 66466
