A damp proof course (DPC) is a vital part of any building’s structure, designed to stop moisture rising from the ground into walls. Without one, buildings can suffer from damp problems that damage brickwork, plaster, flooring, and internal finishes. In some cases, it can even affect indoor air quality.
Whether you’re working on a new build construction, an extension, or a renovation, understanding what a damp proof course is and how they work is essential. In this blog, we explore exactly what a damp proof course is, the different types available, and how to install one correctly to protect your project against moisture.
What is a damp proof course?
A damp proof course is a horizontal barrier built into the walls of a property to prevent moisture rising through capillary action from the ground. This is known as rising damp, which occurs when water travels upwards through porous building materials such as brick, block, and mortar.
In most UK properties, a damp proof course is installed around 150mm above external ground level, as this creates a clear break between ground moisture and the structure above.
Modern building regulations actually require a damp proof course in all new buildings, but many older properties often have a damaged DPC – or none at all – which is why damp issues are a common issue in older buildings.
With a properly installed damp proof course, it helps to:
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Protect internal walls and plaster
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Prevent mould growth and damp patches
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Extend the lifespan of brickwork and masonry
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Improve overall building performance
What are the different types of damp proof courses?
There are several types of damp proof courses, each suited to different building situations and materials. Choosing the right one depends on numerous factors such as the age of the building, wall construction, and whether it’s a new build or remedial project. Choosing the correct one is key to long-term protection.
Some of the most common types of damp proof courses includes:
Plastic (polythene) DPC
This is the most common type used in modern construction. Made from durable plastic or polyethylene, it’s flexible, long-lasting, and resistant to water penetration. It’s best suited for new builds, extensions, and brick and block walls.
Bitumen DPC
Bitumen-based DPCs are typically supplied as rolls or coatings. They create a waterproof layer once it’s applied and are often used where flexibility is required. You’ll typically find this type of damp proof course in floors and foundations, older buildings, or for repairs where plastic DPCs aren’t practical.
Slate DPC
Slate was traditionally used in older properties before modern materials were available. While it is effective, slate DPCs can crack or fail over time. These are most commonly used on heritage buildings, period property repairs, or to match existing materials.
Chemical DPC
Chemical DPCs are injected into the wall to form a water-repellent barrier within the masonry. These are commonly used as a retrofit solution in older properties where no existing DPC has been installed or where the original has failed.
How much is a damp proofing course?
The cost of a damp proof course depends on the type you choose, the size of the area, and whether it’s being installed during construction or as a remedial treatment.
For new builds or extensions, a damp proof course is a relatively small part of the overall build cost, but it plays a major role in protecting the structure. Installing a physical DPC during construction is far more cost-effective than dealing with damp problems later.
For existing buildings, chemical damp proof courses are more expensive due to labour and the preparation work beforehand, but are often the only viable option.
If you’re unsure which type is best for your project, you can speak to one of our experts for advice on avoiding unnecessary costs.
How to install damp proof course
Installing a damp proof course correctly is essential for long-term protection against moisture, which is why we recommend it should be carried by a competent tradesperson. Poor installation can be just as problematic as not having a DPC installed at all.
Whether you’re installing a DPC in a new build or in existing walls, here are some of our tips on how to install damp proof course correctly:
If you’re installing in new builds:
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Ensure the foundations are complete and level
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Lay the damp proof course at least 150mm above ground level
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Place the DPC continuously across the full width of the wall
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Overlap the joints by at least 100mm
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Continue brickwork above the DPC without bridging it with mortar
Remember to take great care to ensure the DPC is not damaged during construction and remains continuous throughout the structure.
If you’re installing in existing walls:
For existing buildings without a functioning DPC, chemical injection is the most common solution, and you can do this by:
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Drillings holes at regular intervals along the mortar line
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Injecting the damp proofing fluid or cream
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Allowing time for the material to cure and form a barrier
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Repairing any plaster internally if required
This process should be carried out carefully, as incorrect spacing or application can reduce effectiveness. As we’ve mentioned, it’s recommended to ensure a knowledgeable professional installs a damp proof course to make sure it’s done correctly and to help avoid any costly damp issues in the future.
Get in touch for advice and a quote
Whether you’re building from scratch, extending a property, or addressing damp issues in an existing building, choosing the right damp proof course is essential.
At JTD Building Supplies, we stock a wide range of damp proof course and building materials suited to any type of project. Our experienced team is always happy to offer practical advice on selecting the right solution for you.
If you need further guidance on types of damp proof courses, or you’d like to get a free quote for materials, don’t hesitate to get in touch with us today and we’ll help you get the job done properly.
Damp proof course FAQs
Do all buildings need a damp proof course?
Under UK building regulations, all new buildings must include a damp proof course. Older properties may not have one, or the original DPC may have failed, which is why rising damp is more common in older buildings.
How do I know if my damp proof course has failed?
Common signs of a failed or missing damp proof course include damp patches on internal walls, peeling paint or wallpaper, crumbling plaster near skirting boards, or a musty smell indoors. If you notice these symptoms, your damp proof course may no longer be effective.
How long does a damp proof course last?
A properly installed plastic damp proof course can last the lifetime of the building. Chemical damp proof courses typically last 20-30 years, depending on the wall condition and the installation quality.
Can I install a damp proof course myself?
In new builds and extensions, installing a physical or chemical damp proof course should be completed by a competent tradesperson to ensure correct coverage and long-term effectiveness.
Is a damp proof course the same as a damp proof membrane?
No. A damp proof course is installed within walls to stop rising damp, while a damp proof membrane (DPM) is usually installed in floors to prevent ground moisture entering the building. Both often work together to provide full moisture protection.
