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  • What is a DPC (Damp Proof Course)?

    13th March 2018

    What is a DPC (Damp Proof Course)?

    If the title hasn’t given too much away a DPC is a damp proof course. The real questions are – what does your damp proof course (DPC) do, where do you find your damp proof course and do all properties have one?


    What does your damp proof course do?

    damp proof course (DPC) in simple terms is a barrier which is designed to prevent damp within a property. The damp proof course is a barrier in the wall which stops water (moisture) rising from the ground and up the walls through capillary action – a process known as rising damp. A damp proof course is normally horizontal but can run vertically where a property is on a hill and the damp proof course needs to step up.

    The video below shows how water rises through a wall. This water can be just low level moisture that rises over time.


    What is the difference between a Damp Proof Course and Damp Proof Membrane?

    You may have heard of the terms damp proof course and damp proof membrane. The differences are outlined below:

    • damp proof course (DPC) is a barrier to prevent water rising up a wall. A DPC layer is usually laid below all masonry walls (load bearing or not).
    • damp proof membrane (DPM) is a barrier or membrane material applied to prevent moisture transmission. This is commonly used under a concrete slab to prevent the slab getting damp through water rising from the ground into the slab. A damp proof membrane can be used as a damp proof course.

    Finally you can also have integral damp proofing where materials are added into a concrete mix to make the concrete itself impermeable and a barrier itself. 


    Where do you find your damp proof course?

    The damp proof course is usually around 150mm from ground level. This is because rain drops typically bounce approx 150mm after hitting the ground and so ensures the wall above the damp proof course is better protected from water saturation. It is often a black material and should be visible (not mortared over). If it is mortared over (often done for aesthetic reasons) the mortar can act as a ‘bridge’ between the brick layers above and below the damp proof course reducing its benefit.

    Diagram showing a damp proof course and damp proof membrane under floor and into walls
    Source: Rentokil


    What is a damp proof course made from?

    A damp proof course can be made from a number of materials of varying rigidity. A few examples are butyl rubber, hot bitumen, plastic sheets, sheets of lead, slate or mortar with waterproofing compounds.

    The oldest material used for a DPC is slate but any water resistant and durable materials can be used. The cheapest and most widely available method is a plastic membrane.


    Do all properties have a damp proof course?

    No. Most properties built in the last 100 years will have a damp proof course installed. However, some older properties were built before damp proof courses were common place and whilst water is drawn up through the walls they naturally dried out through a combination of ventilation and heating. Many building surveyors and specialists would say older properties without them don’t need one added. If they are damp it is usually other factors that need to be resolved to remove the cause damp in the first place (not just try and block the symptoms).


    Is my damp proof course damaged?

    It can be hard to tell. The most obvious sign would be signs of rising damp inside the property in some areas (usually seen as dark stains on the walls). If you are unsure it is best to ask a damp proofing expert to inspect and advise. If you want to use a regulated expert you can check if they are a member of a professional body such as The Property Care Association.

    A damp proof course could become damaged for many reasons such as general deterioration due to its age or movement in the property that causes it to crack or tear. You can either have a new physical barrier installed or look at chemical damp proofing options (there are differing opinions as to how successful chemical solutions are).