A damp proof course (DPC) is a vital part of any building designed to stop rising damp — moisture from the ground that travels up through walls by capillary action. Without an effective DPC, properties are vulnerable to damp problems that can damage walls, plaster, floors, and even structural integrity.
There are two main types of damp proof course:
- Physical DPC – A barrier such as slate, bitumen, or plastic built into the wall during construction.
- Chemical DPC – A modern remedial damp proof course injected into existing walls to block moisture movement.
Why Do Homes Need a Damp Proof Course?
If a property does not have a functioning DPC, water from the ground can rise up the walls — usually up to 400–500mm above floor level. In severe cases, damp can rise even higher, leaving behind visible “tide marks” and hygroscopic salts that cause ongoing moisture problems.
Since 1875, UK building regulations have required new homes to have a damp proof course. Older houses, especially those built before the Victorian period, were typically constructed without one. Early DPCs were often made from slate layers built into the mortar joints above ground level.
Modern Damp Proofing Solutions
At Preservation Treatments, our damp proofing specialists use Safeguard Dryzone, a high-strength silicone-based cream. This chemical damp proof course is injected directly into the mortar bed, where it spreads through the wall and forms a long-lasting water-repellent barrier.
This method is proven to stop rising damp and is widely considered the most reliable rising damp treatment available today.
Frequently Asked Questions About Damp Proof Courses
How much does a damp proof course cost?
The cost of a damp proof course depends on factors such as:
- Wall type (solid brick, cavity, stone, rubble-filled).
- Wall thickness and construction.
- Extent of treatment required.
Because no two properties are the same, a survey by an experienced damp proofing specialist, who are members of the PCA Property Care Association, is essential to provide an accurate quotation.
How long does a damp proof course last?
- Physical damp proof courses (slate or bitumen) can last for many decades. Failures usually happen when the DPC becomes “bridged” — for example, by raised paths, drives, or garden beds externally, or by porous or defective plaster internally.
- Injected chemical DPCs typically come with a 10-year guarantee. However, tests show that when properly installed, they remain effective for much longer.
Where should a damp proof course be installed?
According to UK building regulations:
- A damp proof course should be at least 150mm above external ground level.
- In homes with solid floors, the DPC should link with the damp proof membrane (DPM) beneath the floor.
When installing a chemical DPC, the cream must be injected into the mortar joint, not directly into bricks or stonework. Depending on mortar levels, this may mean the DPC sits slightly above or below the standard 150mm guideline.
Signs of Rising Damp in Your Home
Look out for these common symptoms of rising damp:
- Tide marks on internal walls.
- Flaking plaster or bubbling paint near the skirting boards.
- Musty odours and persistent damp patches.
- Decayed skirting boards or timber.
If you notice any of these, your property may need professional damp proofing treatment.
