A Damp Proof Course (DPC) is used in any walls which rest on foundations laid in the ground to prevent rising damp.
Understanding Damp Proof Courses (DPCs)
Rising damp occurs when ground water is drawn up through porous building materials like brick, concrete, and stone due to capillary action. This can lead to structural damage, mold growth, and health problems. A DPC acts as a barrier to this upward movement of moisture.
Specific Scenarios for DPC Use
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New Construction: During the construction of new buildings, a DPC is essential in walls that are in contact with the ground. It is typically installed at least 150mm above ground level.
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Retrofitting in Existing Buildings: If rising damp is identified in an existing building without a DPC or with a failing DPC, retrofitting a new DPC is necessary. This can be achieved through various methods, including:
- Chemical Injection: Injecting a chemical DPC into the mortar joints.
- Mechanical Insertion: Cutting out a section of the mortar joint and inserting a physical DPC membrane.
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Walls Resting on Foundations: As highlighted in the reference material, DPCs are crucial in any walls that sit directly on foundations buried in the ground. This includes:
- External Walls: The outer walls of the building which are exposed to the elements and ground moisture.
- Internal Load-Bearing Walls: Internal walls that support the structure's weight and are built on foundations.
- Retaining Walls: Although retaining walls have their own considerations regarding drainage, a DPC can be beneficial in preventing moisture transfer into the structure being retained.
Materials Used for DPCs
Common materials used for DPCs include:
- Bituminous Felt: A traditional and cost-effective option.
- Plastic or Polyethylene: Durable and resistant to degradation.
- Slate: A natural and long-lasting material (though less common now).
- Engineering Bricks: Bricks with very low porosity, sometimes used as a DPC.
- Chemical Injection Fluids: These create a water-repellent barrier within the wall.
Important Considerations
- Bridging: Avoid "bridging" the DPC, meaning preventing anything like soil, render, or plants from creating a path for moisture to bypass the DPC.
- Proper Installation: Correct installation is critical for the DPC's effectiveness. Seek professional advice if unsure.
- Drainage: Effective site drainage can reduce the amount of water present around the building's foundations, complementing the DPC.
In conclusion, a DPC is necessary for any wall resting on foundations laid in the ground to prevent rising damp and protect the building's structure and inhabitants.
