A traditional (physical) damp proof course (or DPC) is an impervious layer built into a wall, which prevents moisture from the ground rising up the wall via capillary action. A remedial / chemical damp proof course is an injected product, which coats the capillaries in the wall substrate to prevent the movement of water from the ground.
Without a damp-proof course, dampness from the ground may move from the ground into the wall structure. In most cases, this will be to a height of around 400 – 500mm above floor level. In some cases, usually where there are high concentrations of hygroscopic salts, it may rise to a higher level in the wall, which can result in a visible ‘tide mark’ showing the extent of dampness in the wall substrate.
A DPC has been a requirement in house building for many years now.
What is a damp proof course made of?
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.
Houses built before the Victorian period in the mid 1800’s were usually built without a damp proof course. By 1875, the inclusion of a DPC became compulsory in properties being built in London; which naturally spread throughout the country. At that time, it would have been a single, or double layer of slate built into the structural walls, at the correct position above external ground level. This would usually be two mortar courses above external ground levels.
Where we are dealing with a rising damp problem in a building, Preservation Treatments will generally be specifying the injection of a high strength, silicone-based cream. The cream diffuses through the wall substrate to begin the process of drying damp affected walls by preventing continued dampness from the ground, rising into the walls. The product we use is Safeguard Dryzone, which is proven to have the highest percentage of active ingredient.
Frequently asked questions about damp proof courses
- How long does a damp proof course last?
- How much is a damp proof course?
- Where should a damp proof course be installed?
How much is a damp proof course?
This is one question where the answer is … it depends. To answer it in a specific case, one of our experienced Surveyors will carry out a site inspection. The cost is dependent on several things, including: type and thickness of walls, extent of treatment needed, whether the walls are solid brick, stone or rubble-filled stone, or if the walls are cavity construction.
How long does a damp proof course last?
Most physical damp proof courses, such as double layer slate DPC’s, or bitumen felt DPC’s will last for many years. The reasons for failure which could lead to rising damp are often due to the original DPC being “bridged” by external paths, drives and gardens etc, being built on top of previous paths and drives, which result in the DPC being below the present, existing external ground levels.
When it comes to remedial, injected damp proof courses, the industry standard is to provide a ten year guarantee. However, tests carried out by the manufacturer confirm the injected cream, when used properly, will last many years more than the guarantee.
Where should a damp proof course be installed?
Building regulations state that; A DPC should be provided a minimum 150mm above adjoining, external ground surfaces and, if the ground floors are solid construction, should be linked with the DPM in solid floors.
When installing a remedial, injected DPC, we would always attempt to adhere to the same guidance. However, as a remedial DPC should be injected into the mortar course and not into the brick or stone, it is dependent on the height of the mortar courses above ground levels. Therefore, its level may be slightly under, or slightly over 150mm above ground levels.
Is your property affected by rising 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