Building guidance generally expects the damp proof course to be at least 150mm above the outside ground level. That gap stops rain splashing up above the DPC and stops soil or paving bridging it, so if your path, patio or flowerbed is higher than that, it can cause low-level damp inside.
If I could give homeowners one free tip that would save them money on damp, it would be this: go outside and look at how high the ground is against your walls.
The 150mm rule of thumb
Building guidance generally looks for a gap of at least 150mm between the outside ground level and the damp proof course. There are two good reasons. First, rain hitting a hard surface splashes up the wall, and if the DPC is too close to the ground the splash wets the brickwork above it. Second, soil and paving in contact with the wall above the DPC give ground moisture a path straight around it.
How ground levels creep up
- New patios and driveways laid on top of old ones, or built up to make a level step out of the back door.
- Flowerbeds and raised beds built against the house.
- Years of soil, bark and gravel being added to borders.
- Paths that slope towards the house so rainwater runs to the wall and sits there.
Inside, the result is usually damp low on the wall in the room behind, peeling skirting-level decorations and, over time, salt damage to the plaster.
Finding your DPC
On older brick houses the DPC is often visible as a thicker mortar line, a line of slate, or a strip of black bitumen felt a few courses up from the ground. Air bricks for a suspended floor are usually just above it. If you can’t find it, or the ground is right up at the air bricks, that’s a sign to investigate.
Putting it right
- Lower the soil or remove the raised bed against the wall.
- Where a path or patio is too high, the best fix is to lower it or cut a strip out next to the wall. Fill that strip with gravel over a drained base or fit a channel drain, laid to fall away from the house.
- Make sure paving falls away from the house, not towards it.
- Don’t dig down below the level of the foundations or undermine the wall. If in doubt, get advice before you start.
- Keep air bricks clear of soil and paving.
Once the ground is lowered, the wall needs time to dry. If the damp inside persists after that, it’s time for a proper survey.
When to call a specialist
If you're not sure where your DPC is, or the ground can't easily be lowered, get a survey to confirm what's causing the damp and the safest fix. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Frequently asked questions
What is the minimum gap between ground level and DPC?
Guidance generally looks for at least 150mm.
Can a new patio cause damp?
Yes, if it's laid too high or slopes towards the house it can bridge the DPC and cause splashback.
Is a gravel strip next to the house a good idea?
A properly drained gravel strip can help where ground levels can't easily be lowered.