A damp proof course (DPC) is one of the most important yet often overlooked elements of a building’s structure. It prevents moisture from the ground from rising through walls and floors, protecting your home from long-term damage such as mould, decay and structural issues.
In this guide, we explain what a damp proof course is, why it is required in UK homes and how to spot problems or failures. We also cover modern alternatives and what UK Building Regulations say about damp proofing.
What is a damp proof course?
A damp proof course is a barrier, usually a layer of impervious material, built into the walls of a property just above ground level. Its purpose is to stop rising damp, which occurs when groundwater travels upwards through porous building materials such as brick or mortar.
Traditionally, DPCs were made from slate or bitumen felt, but today you will also find plastic membranes (polyethylene) and chemical injection DPCs in modern builds and renovations.
According to the NHBC Standards, all new UK homes must include a properly installed damp proof course as part of their structural design.
Why a damp proof course is necessary in the UK
The UK’s wet, temperate climate makes damp control essential. Without a DPC, moisture can rise up through the walls by capillary action, leading to rising damp, a problem that affects thousands of homes each year.
Common issues caused by rising damp
- Peeling or bubbling paint and wallpaper
- Salt deposits forming on internal walls
- Damp, musty smells
- Rotting skirting boards or floor timbers
- Mould growth, which can trigger health issues
The UK Building Regulations Approved Document C requires that walls and floors are constructed to prevent moisture ingress from the ground. Installing a proper DPC is therefore a legal requirement for all habitable buildings.
Types of damp proof course used in UK properties
Modern DPC systems come in various materials and forms depending on the building’s age, design and budget.
Physical damp proof courses
- Polythene or plastic membrane DPCs – Common in newer homes, flexible, durable and rot-proof.
- Bitumen felt or slate DPCs – Found in older buildings, offering long-term resistance when properly installed.
Chemical injection DPCs
- Used in remedial damp proofing for existing properties.
- Silicone-based creams or liquids are injected into mortar joints to create a water-repellent barrier.
- Suitable when the original DPC has failed or was never installed.
For professional guidance, the Property Care Association (PCA) provides detailed information about certified damp proofing specialists in the UK.
How to tell if your damp proof course has failed
A DPC can deteriorate or become bridged over time. Look for these signs:
- Tide marks or discoloured plaster along lower walls
- Flaking paint or crumbling plaster at skirting height
- Wet patches that do not dry out even in summer
- Rotting skirting boards or floor joists
If you suspect a problem, have a qualified damp surveyor inspect your property. The Royal Institution of Chartered Surveyors (RICS) offers a directory of accredited professionals.
How a damp proof course is installed or repaired
If a DPC is missing or ineffective, there are several solutions:
- Chemical injection – Creams such as silane or siloxane are injected into drilled holes in the mortar joints to form a new barrier.
- Electro-osmotic systems – Use an electric charge to repel moisture, typically for heritage or listed buildings.
- Physical membrane replacement – In severe cases, a new DPC layer can be cut in and re-laid, though this is costly and disruptive.
Always use certified contractors. Improper installation can lead to ongoing damp problems and invalidate insurance or warranty coverage.
How much does damp proofing cost in the UK?
Costs depend on the method and severity:
| Method | Average cost (2025) | Typical application |
|---|---|---|
| Chemical injection DPC | £60–£80 per linear metre | Most standard brick walls |
| Electro-osmotic DPC | £1,500–£3,000 total | Heritage or listed buildings |
| Physical membrane replacement | £2,000–£6,000+ | Full structural remediation |
Estimates based on data from Checkatrade and UK damp specialists.
Can a damp proof course be retrofitted in older homes?
Yes. If your property predates the 1875 Public Health Act (when DPCs became mandatory in the UK), it may not have a damp barrier at all. Modern chemical injection or electro-osmotic systems can be installed without major disruption, making them ideal for Victorian and Edwardian properties.
Preventing future damp problems
Even with a good DPC, moisture can still enter your home if:
- External ground levels are raised above the DPC line (bridging the barrier)
- Leaking gutters, downpipes or poor drainage cause splash-back onto walls
- Mortar joints or render are damaged
Regular maintenance, proper ventilation and keeping the DPC line visible will prevent most damp problems.
What to remember:
- A damp proof course stops rising damp by forming a barrier within your walls.
- It is a legal requirement under UK Building Regulations for habitable dwellings.
- Regular inspection and maintenance help avoid costly structural repairs.
- If in doubt, consult a qualified damp specialist for professional advice.
