How Do I Know Where My Damp Proof Course Is?

Noticed bubbling paint, musty smells, or stains creeping up your walls? You could be looking at rising damp — and your damp proof course (DPC) is the first thing to check.

So, where is it?

In most homes, the DPC is a thin horizontal barrier about 150mm (6 inches) above ground level, running through the base of your exterior walls. It may look like a plastic strip, slate layer, or simply a line in the mortar.

This guide will show you how to find it, check if it’s working, and understand what to do if it’s hidden, damaged, or missing altogether.

Let’s cut through the guesswork — and help you keep damp where it belongs: outside.

Understanding the Damp Proof Course

A DPC is a hidden barrier built near the base of your walls to stop moisture rising from the ground. It prevents water from soaking into the brickwork — much like a sponge — and protects your home from rising damp, salt stains, flaking paint, and timber decay.

DPCs have been required in UK homes since the 1875 Public Health Act, but in older buildings, they may be missing, damaged, or made from materials like slate or bitumen that break down over time.

A working DPC:

• Blocks rising damp

• Protects internal finishes

• Prevents rot and mould

• Reduces salt build-up on walls

Common DPC Materials by Era

Where to Expect the DPC on Your Property

In most UK homes, the DPC sits about 150mm (6 inches) above external ground level — roughly the height of two bricks. This keeps it clear of rain splash, rising soil, and surface water.

It may appear as:

• A thin plastic strip in the mortar

• A slate or bitumen layer in older homes

• Hidden in both wall layers in modern cavity constructions

If it’s not immediately visible, check all sides — landscaping or finishes may obscure it.

Common Mistakes When Looking for a DPC

So, you’ve got your torch, your measuring tape, and maybe even your damp meter — but somehow, you’re still not sure if what you’ve found is the DPC. Don’t worry — this is incredibly common.

Here are some of the most frequent slip-ups homeowners make during their DPC hunt — and how to avoid them.

Misidentifying Visual Features

It’s surprisingly easy to confuse architectural details for a damp proof course. After all, homes have lots of horizontal elements at low levels, and not all of them are moisture barriers.

Here’s what people often mistake for a DPC:

• Plinth bricks – These are slightly protruding or decorative courses near the base of the wall, especially in older homes. They’re aesthetic, not functional.

• Drip edges – Found beneath window sills or projections, these help rainwater fall away from the wall, but they don’t block rising damp.

• Air bricks – Ventilation openings for suspended timber floors. These help with airflow under the floor but are placed above the DPC, not part of it.

• Decorative banding or pointing – Some properties use contrasting bricks or mortar for style. It may look like a line, but it’s not a moisture barrier.

🔍 Quick tip: A real DPC typically cuts straight through the mortar joint, sometimes with no projection or texture at all. If it’s raised or clearly intentional, it’s probably not a DPC.

Assuming Newer Homes Always Have One Visible

Here’s a myth worth busting: Just because your house was built after 1980 doesn’t mean your DPC will be obvious.

In many modern homes, DPCs are:

• Concealed beneath render or cladding

• Integrated into the cavity wall construction

• Buried by raised patios, driveways, or external insulation

You may also find that the outer DPC is completely hidden while the inner wall uses a damp proof membrane (DPM) under the floor slab, connected to a cavity tray. In other words, it’s doing its job — but you’ll never see it.

If you can’t spot a DPC, don’t assume it’s absent or failed. You might just need to look more closely, or from a different angle.

Signs That May Reveal Its Location

So if your DPC is hard to spot — or entirely invisible — how do you find it?

The good news is that your home leaves clues. Some are visible from the outside. Others can be found inside, especially when moisture starts to cause trouble.

Exterior Clues

Step outside and take a slow walk around your house. These are the things you should be looking for:

• A thin plastic strip (usually black or grey) running horizontally through the mortar joint

• A slate course embedded within the bricks, common in older homes

• A dark line or band of bitumen that appears slightly different from surrounding materials

• A change in brick tone or texture along a horizontal line — possibly due to different materials or repairs

⚠️ Be aware that not all walls reveal their secrets immediately. Look near downpipes, service boxes, or outdoor taps — places where render may have been broken or never applied.

Interior Symptoms of a Failing or Bridged DPC

If the DPC has failed — or been bridged by something like render or a raised flowerbed — the interior often tells the story.

Look out for:

• Damp patches at the base of walls, especially in corners or near chimneys

• Blistering or flaking paint, often accompanied by a salty white residue

• Peeling wallpaper, especially around skirting boards

• Rotting skirtings or musty smells that linger no matter how much you air the room

One critical clue: rising damp rarely goes above 1 metre in height. That’s the limit of capillary action. So if the damage stops around that level, the DPC may be missing, breached, or failing.

Can’t Find a DPC? Here’s What to Check and What to Do

If you’ve inspected your property and can’t find a damp proof course (DPC), don’t panic. It doesn’t always mean you’re unprotected — but it does mean it’s time to dig a little deeper.

Whether the DPC is simply hidden or truly missing (especially in older homes), this section will help you assess your situation and take the right next steps.

1. Is It Hidden — or Was It Never There?

In many homes, especially those built after the 1875 Public Health Act, a DPC is present — but may be concealed. Common reasons include:

• Render or cladding applied too low

• Landscaping or patio work bridging the DPC

• External insulation systems covering original brickwork

• Cavity wall construction hiding the DPC within both wall layers

On the other hand, if your home predates 1875, it may never have had a DPC at all. Older buildings relied on breathable materials (like lime mortar) and natural ventilation to manage moisture.

2. Run Some Simple Checks

You can investigate further without causing any damage:

• Use a moisture meter: High readings near the base of walls that taper off higher up can suggest rising damp.

• Check behind skirting boards or furniture: Look for bubbling paint, salt deposits, or damp patches.

• Inspect exterior walls again: A slate, plastic, or bitumen line may be visible above ground level — sometimes in corners or near service boxes.

• Review property drawings or renovation records: Previous surveys, plans, or retrofit documents might reveal where the original DPC line was — or confirm that one was never installed.

3. When to Bring in a Specialist

If these checks don’t give you clear answers — or you’re seeing signs of persistent damp — it’s worth getting a professional involved.

A qualified PCA- or CSRT-accredited surveyor can:

• Confirm whether rising damp is present or if another issue is at play (e.g., condensation, plumbing leaks)

• Use tools like deep-wall probes and thermal imaging for accurate diagnosis

• Offer pressure-free advice on treatment options

This is especially important before undertaking renovations or purchasing a property.

4. If Your Home Lacks a DPC

If it turns out your property was never fitted with a DPC — or had one that failed completely — you still have options.

Some older buildings are better suited to traditional moisture management techniques, such as:

• Breathable lime plaster and mortar

• Underfloor ventilation

• Moisture-tolerant finishes

However, if rising damp is a problem, modern solutions can be added:

• Chemical injection – Forms a new barrier inside the wall with minimal disruption. Best for brick walls.

• Electro-osmotic system – Uses low-voltage wires to redirect moisture. Ideal for stone or variable walls.

• Physical retrofit DPC – Involves cutting into the wall and inserting a new membrane. Highly effective, but more invasive.

Most treatments are followed by salt-resistant replastering to ensure long-term protection.

If you can’t find a DPC, don’t assume the worst — but don’t ignore the signs either. A few simple checks can point you in the right direction. And if you’re still unsure, a professional surveyor can give you answers — and peace of mind — without tearing your home apart.

Final Takeaway: Know Your DPC, Protect Your Home

Locating your damp proof course — or realising it might not be doing its job — can feel daunting. But with the right approach and support, it’s entirely manageable.

If signs of damp are raising questions you can’t quite answer, that’s where a knowledgeable partner makes all the difference.

Ex10 specialises in diagnosing and resolving damp-related issues, from hidden or failed DPCs to complete treatment solutions. With their experience and clear, honest assessments, you’ll get the answers — and the fix — without the pressure.

Sometimes peace of mind starts with knowing who to call.

Need help with damp? Contact Ex10: 01202 618240