Defective Or Bridged Damp Proof Course

A damp proof course (DPC) that is either faulty or bypassed is a common and serious issue in buildings, especially older ones. This problem can lead to rising damp, a condition where moisture travels up through the walls, resulting in both structural damage and health concerns. To effectively resolve the issue, it is essential to understand the distinction between a defective DPC and a bridged one.

What is a Damp Proof Course (DPC)?

A Damp Proof Course is a waterproof layer installed low in a wall. Its purpose is to block groundwater from being drawn upwards into the building’s masonry through a natural process known as capillary action. Historically, DPCs were made from materials like slate or bitumen, but contemporary construction typically uses a durable plastic membrane that is installed when the building is erected.

What is a Defective Damp Proof Course?

A DPC is considered defective when the physical barrier itself has failed. This breakdown can occur over time as the material ages, when the building settles and causes the DPC to crack, or if it was installed improperly. When a DPC is compromised in this way, it loses its continuous barrier, allowing moisture to get past it and rise into the wall structure.

What is a Bridged Damp Proof Course?

Bridging happens when moisture finds a path to get around a DPC that is still intact. A frequent cause of this is when external features like garden beds, paths, or soil are built up to a level higher than the DPC. It can also occur when plaster or render is applied over the DPC line, creating a “bridge” for moisture to travel across. In this scenario, the DPC itself isn’t broken, but its protective function is bypassed.

Signs of a Defective or Bridged DPC

You may have an issue with your DPC if you notice:

• Visible damp patches or “tide marks” appearing on the lower sections of walls.
• Paint or wallpaper that is blistering, bubbling, or peeling away from the wall.
• A white, powdery substance on the wall’s surface, which is salt deposits known as efflorescence.
• A persistent musty or damp odour in the affected area.
• Skirting boards or floor timbers that show signs of rot and decay.

Consequences of a Defective or Bridged DPC

If left unaddressed, a faulty DPC can lead to significant problems, including:

• Structural Damage: Long-term dampness can degrade plaster, corrode metal wall ties, and cause timber elements like joists and floorboards to rot, weakening the building’s overall integrity.
• Health Issues: The damp conditions create an ideal environment for mould and mildew to grow. These can release spores into the air, potentially triggering allergies, asthma, and other respiratory conditions.
• Reduced Property Value: The visual evidence of damp, combined with the underlying risk of structural issues, can significantly lower a property’s market value and make it difficult to sell.

How ABIS Can Help

Determining the exact cause of rising damp requires a professional evaluation. An ABIS building inspector has the specialised knowledge and equipment to accurately identify whether your DPC is defective, bridged, or if the damp is coming from another source entirely. Our in-depth reports will specify the cause of the issue and outline the best course of action, helping you protect your investment.

Wikipedia Entry for Damp Proofing