What is a Damp Proof Course (DPC)?

If you’ve noticed rising damp in your London property, this could be due to damage to your damp proof course or in some cases, your property completely lacking one at all. Both DPC repair and installation will help to prevent rising damp problems, allowing your walls to stay clean, structurally solid and free of moisture. Now let’s explore what a DPC is in more depth.

What Exactly is a Damp Proof Course?

Damp proof course is the name given to the protective layer between your property and the external ground. The name applies to the application and the role that the damp proof course plays rather than the specific material used, meaning that there are many different types of DPC and your property will generally only use one of these.

The most common type is the physical and visible DPC, often a type of thin waterproof material such as lead-lined bitumen, slate or plastic. These DPCs look like fine sheets of material situated between the brickwork of a building near ground level and can also be referred to as damp proof membranes. The presence of this waterproof barrier is to prevent groundwater from being absorbed into your building’s masonry by capillary action. Groundwater can naturally be drawn up through the small holes within your property’s mortar and result in rising damp issues; the damp proof course prevents this from occurring by stopping the water only a short distance from the ground.

The DPC should be at a lower point than any materials used in timber suspended floors to prevent wet/dry rot or internal décor finishes (plaster and paints of wallpapers etc) that could spoil due to salting, de-bonding (blown or live plaster). The existence of damp wall defects can be hidden at times where tiled or timber clad internal walls exist.

The other most common type of DPC comes in the form of a chemical rather than a physical barrier. Chemical DPCs are often injected into the brickwork/mortar of your property near ground level (approximately 150mm above the external ground level) to provide a waterproof layer within the mortar, this is usually the result of remedial works. Chemical DPCs can be made from a variety of different products and chemicals but tend to appear as gels or creams. This is the type of treatment that your property may undergo if your damp proof membrane is damaged or missing, as introducing a new physical damp proof membrane can be difficult, time-consuming and expensive in comparison.

A DPC Glossary of Terms

Having discussed exactly what a damp proof course is, there is some key DPC-related terminology worth learning to stay fully aware of what is happening to your property. Here is a short guide to some phrases you might hear a damp proofing contractor say:

• Bridging of the DPC – This occurs when dirt or other substrate is piled/built up against the external wall and above the damp proof course, causing moisture to bypass the DPC entirely. Bridging can also occur if structures like paths, patios, garden walls are built in line with the DPC, allowing damp to bypass it and rise above the membrane
• Capillary Action – The movement of moisture from within the ground up into the brickwork and render via smalls pores in the building material (the cause of rising damp)
• Rising Damp – The term given to damp that occurs from moisture rising upwards from the ground into your walls
• Penetrating Damp – The term given when moisture is absorbed into the exterior brickwork and seeps into the property, leaving interior brickwork and plaster damp

When it comes to DPC repair work or damp proofing carried out in your property, it’s good to have an idea of the type of terms that may be used so you aren’t left confused from a survey or report.

At Garratt’s Damp, we specialise in providing holistic damp proofing for both residential and commercial properties. Our team of experts will gladly visit you and provide a survey of your damp concerns, recommending the most efficient solution for your personal needs or requirements. Book a survey today or get in touch on 0208 535 7536 for bespoke advice tailored to you.