What A DPC Actually Does
A damp-proof course is a barrier built into a wall, usually a couple of courses above ground level, that stops moisture from the ground travelling upward into the brickwork above.
“A DPC is a physical barrier to prevent ground water rising through a wall.” — RICS
Most homes built from roughly the 1870s onwards have one – originally a layer of slate or engineering brick, later bitumen felt, and now usually a plastic membrane. Older properties without a DPC rely on different construction methods entirely, which is its own separate topic.
How A DPC Gets “Bridged”
Bridging means something is giving moisture a way to get past the DPC without going through it – so even a perfectly intact DPC stops doing its job. This is far more common than an actual failed or missing DPC.
Common Ways A DPC Gets Bridged
In every case, the DPC itself can still be working exactly as intended – moisture is simply finding a route around it, not through it.
Why This Matters For The Fix
If a DPC is bridged rather than failed, replacing or re-injecting it doesn’t solve anything – moisture will keep bridging the new one exactly as it did the old one. The actual fix is usually removing whatever’s causing the bridging: cutting render back above ground level, lowering a path, clearing debris from against the wall, or moving a flower bed.
This is exactly why we check the whole picture – render lines, external ground levels, paths, gutters – before recommending any DPC work, rather than assuming a damp patch near the floor automatically means the DPC has failed.
The Bottom Line
A damp patch near the bottom of a wall doesn’t automatically mean the damp-proof course has failed. More often than not, something external is bridging a DPC that’s still doing its job – and fixing that is usually simpler, and cheaper, than a full re-injection.
Frequently Asked Questions
How do I know if my DPC is bridged rather than failed?
Look at what’s happening outside at the same height as the damp: raised ground, a path or render running down to ground level are strong indicators of bridging. A proper inspection checks this before assuming the DPC itself needs work.
Does a bridged DPC need to be replaced?
Usually not. If the DPC itself is intact, removing whatever’s bridging it – render, raised ground, debris – is often enough, without any injection or replacement work.
Can a damp-proof course fail on its own over time?
Older physical DPCs (slate or bitumen felt) can deteriorate or crack with age or ground movement, but this is less common than bridging. Either way, it’s worth ruling bridging out first since it’s the simpler and more frequent cause.
What if my house doesn’t have a damp-proof course at all?
Many older and traditional properties were never built with one, and rely on different, breathable construction methods instead. Treating them as if they should have a modern DPC can cause more problems than it solves – see our guide on damp in older and traditional buildings.
Not Sure If It’s The DPC Or Something Bridging It?
Get in touch and we’ll check the whole picture before recommending anything – including whether the DPC needs any work at all.