Home > What To Do > Avoiding the DPC When Laying a Driveway

Avoiding the DPC When Laying a Driveway

By: Chris Hogan MSc - Updated: 21 Feb 2021 | comments*Discuss
Dpc Driveway House Damp-proof Course

The damp-proof course (DPC) of a house is of paramount importance in keeping damp at bay. If your new driveway bridges the DPC, then you could be letting yourself in for a whole host of problems.

What is the Damp-Proof Course?

The idea of a DPC is to prevent the water in the ground from being drawn up into the walls of the house by a process known as capillary action. The bricks act like sponges, although they aren't that efficient, but over time water can get pretty high up a wall. This leads to damp problems, with plaster damage and mould forming on walls, which can cause respiratory problems for people in the house.

Putting a waterproof barrier (the DPC) a few courses of bricks above ground level prevents the water rising past that level. Modern houses will have a layer of black polyethylene which is flexible and comes on a roll. This can usually be seen outside, just above ground level. Older houses might have slate or a row of clay bricks, both of which are denser and more resistant to capillary action.

Dangers of Bridging the Damp-Proof Course

Provided that the DPC isn't broken or bridged then it will probably do its job for as long as the house stands. Bridging is more likely to be a problem with driveways, although it's not exclusive to them. Bridging occurs when the ground level outside the house rises up, for what ever reason, so that it is above the DPC.

This means that water can get at parts of the wall that are unprotected, allowing damp to start entering the house higher up the walls. This often happens as a result of soil building up on flower beds adjacent to the house, but you need to be aware of it with driveways, too.

Driveway Installation

Bridging is most often a problem when renewing or constructing a driveway or path means raising the ground level to a point where it gets too close, or even above, the level of the DPC. This must of course be avoided, although it still happens today, usually when a householder has been tempted into using an unqualified or unscrupulous driveway contractor.

The current minimum distance from the exterior ground level to the DPC is 15cm (about 6in) as specified in the England and Wales building regulations. But older DPC's may be lower than this and many will be a lot higher, particular with houses built on sloping ground. In fact, a DPC may be stepped to cope with the change in ground level around a house.

So if the height of the driveway brings the ground level up to less than 15cm (6in), then the driveway design will have to change to cater for it. If excavating to lower the whole of the driveway is impractical or too expensive, the solution is to create a gap between the driveway and the wall of the house. But the gap must have Good Drainage.

Drainage Channel

How you achieve that good drainage depends on the lie of the site, the access to existing storm drains and gullies, and the likelihood of heavy rain in the area. If there is good access to the storm drains and the fall of the channel can be engineered so that there is a good slope to the drains, the gap can be left empty. Consider lining the bottom with a dished paving slab to encourage water into the centre.

If drainage isn't as good, you'll need to slow the water down in the gap itself, so consider placing a perforated drainage pipe in the channel then filling it with gravel. A raised lip on the edge of the driveway adjacent to the channel, perhaps using a slightly proud kerb stone, will help steer water away from the channel and ease the drainage problem.

Levels are Important

Pay particular attention to levels when planning the rest of the driveway, putting in falls where you can get away with it that will divert rain water away from the problem area.

Get Ready for Rubbish

But finally, be aware that the gap tends to be attractive to all sorts of windblown rubbish. So keep it as narrow as possible, so that it's not a danger to pedestrians, but wide enough to get hands or brushes in to sweep it out.

You might also like...
Share Your Story, Join the Discussion or Seek Advice..
[Add a Comment]
I just had my resin bound driveway installed with block edging, however, the distance from DPC is a single brick. Resin bound is fully permeable, can this still become an issue on the structure (or even future surveys)?
MikePlits - 20-Dec-20 @ 3:42 AM
Hi, I am having a driveway installed and they have built almost pass the skirt of the house. One airbrick is still completely exposed and a 0.5cm from the paving and the other is lower than thr drive and they have built a small trench the width of the air brick so that it isnt blocked by the brickwork. I'm concerned about damp because how far they've built up the house. They did not discuss this with me before they built the drive like that. I've asked them why they haven't put a trench in so that they is a gap away from house so that the airbricks and damp course are not compromised. They are telling me because I didn't discuss this with them I will have to pay for this change. I would have thought that they would have known to build a trench as standard it they can't level drive down. Please help
GeorgieR - 15-Oct-20 @ 11:06 PM
Hi, I am buying a house that appears to have both front and back pathways bridging the exisiting damp course. The cottage is, about 1900, and terraced, but there does appear to be some damp half way up the first brick, and in the front some pooling of water after heavy rainfall. I am content to still buy but not if the works required are going to be extensive and cost considerably more than purcahse price. How is such a problem rectified? Can it be done easily? Many Thanks Julie
Julien - 23-Jul-20 @ 3:31 PM
Just having a block drive put down. They're putting drains all around the exterior wall of the house as the drive slopes from road to house. These lead directly into the drains. My problem is that after reading about the subject the level of the drive needs to be two bricks (6 inches) below the level of the DPC. I understand the DPC to be the mortar bed above the ring of blue bricks, so there should be two courses of bricks showing (the blue ones and the ones below). Well, they had the top of the plastic drain channels half-way up the blue bricks. After questioning this, and speaking to the company owner, they've lowered them to the bottom of the blue brick (so one course below the DPC). Is this acceptable?What would building regs say about this? I'm concerned on 2 fronts:- would this cause a problem with a survey if we ever try to sell? are we likely to suffer from damp? Like I mentioned, the plastic channel (itself around 4-5 inches deep by the looks of it) separates the blocks from the wall of the house, but I'm just as concerned by the possibility of splashes entering the air bricks, which are literally above the DPC. Any advice (urgent as they are currently working on the house) would be gratefully received. Cheers
Malcolm - 11-Mar-19 @ 5:02 PM
Hi I am buying a house and the external ground level to the front of the property is too high in relation to the damp proof course. The damp proof course to rear is level with the flagged path adjacent the kitchen door. How can this be fixed? Can i just dig??
Sally - 18-Sep-13 @ 11:46 AM
We had a block paved drive laid about 4 years ago and have had no issues with it whatsoever. We are looking to sell the house and have been advised that the block paving is too close to the DPC (less than 150mm) along a section of the house front. The DPC is stepped at the front (from the back and side) due to the slight slope of the land and I understand that the paving at the front is closer to the DPC to match the paving of the neighbouring property and avoid run off on to our property. After research on the web, I'm led to believe a small trench should have been utilised by the contractor?
Nikster - 9-Feb-12 @ 10:26 PM
Share Your Story, Join the Discussion or Seek Advice...
(never shown)
(never shown)
(never shown)
(never shown)
Enter word:
Latest Comments