What is a damp proof course?

damp proof course (DPC) is a key weapon in the fight against damp homes. Damp is one of the most common property problems encountered in British homes and can cause significant problems.

Often it is damage to the appearance of a property that people notice first, but it is the structure of the property where the real problems occur. Cracks to masonry, crumbling plaster and rotting timbers are all common consequence of damp, not to mention the damp inside the home causing mould and damage to furnishings, and even more worrying to your health.


The damp proof course is, most commonly, a layer of damp proofing material or slate laid between the bricks near to ground level of the property when the property is being built. If installed correctly it should stop damp rising from the ground into the walls of the property. There’s no real figures available that say how long this style of damp course actually lasts. Properties that were built in the 1930s – 1960’s would mean this type of damp proof course is well over 50 years old.

DPC’s also work in conjunction with cavity walls by taking moisture that enters the cavity and channelling it back out of the property. If a damp proof course fails or is absent they are often replaced by a chemical damp proof course.


A chemical damp proof course can usually be recognised by the small drill holes that it leaves behind when the perimeter of the building is drilled for the chemical damp course to be sprayed into these holes. The above graphic is a perfect example of where the chemical damp course has been done directly above where the original damp proof membrane would have been.

A missing damp proof course, or one that has been compromised by rendering over it, meaning the wall below the damp proof has been bridged with the wall above the damp proof, is one of the main reasons for failed cavity wall insulation. In these instances, damp will not be able to exit the cavity, leading to damp insulation material which can then affect the internal wall.

A DPC is just one form of damp proofing, other popular methods include:

  • Damp-proof membrane (DPM) is a material such as polyethylene applied to prevent moisture moving through the property.
  • Integral damp proofing can occur in the construction stage by adding materials to the concrete mix which repel moisture.
  • Waterproofing the exterior of the building to offer additional resistance against rain.
  • Pressure grouting cracks and joints in masonry to resist the ingress of water.

Many people react to damp issues by sealing their properties, but it is often the opposite approach, allowing your home to breathe, which is the right approach.

If your home cavities have been insulated with rock wool and are exposed to damp, the rock wool will sook up a considerable amount of water and retain it. QUICK VIDEO

This will make the wall cold and damp, drawing heat from the inside of the home to the outside, having the opposite required effect for what it was installed for, and can allow moisture to travel inwards and cause damp and mould in your home.

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1 Comment

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