What a damp-proof course does
A damp-proof course (DPC) is a waterproof layer built into the wall a little above ground level. It stops moisture in the ground, and rain splashing off the ground, from rising up the brickwork into the house. Approved Document C, the government's building regulations guidance on moisture, says the DPC in an external wall should be at least 150mm above the finished level of adjoining ground or paving.
The 150mm gap is there because rain bounces. On a hard patio, heavy rain splashes up the wall; if the paving is close to the DPC, that water lands above it and soaks in where nothing stops it.
How to find the DPC on your house
- Look for a line in the mortar a few courses above the ground: a thin black (bitumen), grey (plastic) or slate layer in the joint.
- Look for a change in brick: some houses have dense engineering bricks below the DPC.
- Look for injection holes: a row of small filled holes along a mortar joint means a chemical DPC was injected later.
- Check the floor level inside: the DPC is usually at or just below internal floor level.
- Find the air bricks: these ventilate a suspended timber floor and sit just above or around DPC level.
If you cannot find it, assume it is close to the internal floor level and keep the patio well down.
Why Darlington homes vary
Darlington's housing ranges widely, and the DPC position varies with it.
- Old village cottages around Cockerton Green and in Hurworth and Haughton-le-Skerne date back to the 17th, 18th and 19th centuries. Some have no physical DPC at all, or a chemical one added later, and floor levels can be very close to the outside ground.
- Victorian and Edwardian houses in the West End Conservation Area, Darlington's largest, often have a slate DPC and suspended timber floors with air bricks that must stay clear.
- 1930s to 1960s semis in Harrowgate Hill, Mowden and Blackwell usually have a clear DPC line and air bricks low on the wall.
- Modern homes in West Park and Middleton St George often have patio doors at floor level with little height to spare, which is where most level problems start.
Air bricks: never bury them
Air bricks let air under suspended timber floors. Paving over or raising the ground against them blocks ventilation and can lead to damp and rot in the floor. Where a patio has to sit near an air brick, the patio stays below it, or a vented periscope or a gravel strip with a small gap keeps the airflow open.
When the patio cannot finish 150mm down
Sometimes the garden is higher than the house, or the owner wants a step-free threshold. We have three main ways to deal with it.
Lower the ground
Dig the area next to the house down, then step up to the garden with a low retaining wall or steps. This is the most reliable answer and keeps the house dry.
A gravel or channel strip against the wall
A strip of free-draining gravel between the patio and the house, with a drain beneath, stops splash and keeps water away from the brickwork. It is a common detail on older terraces where every centimetre counts.
A linear drain at a level threshold
Outside bi-fold or French doors, a slot or channel drain set right against the threshold collects water before it can reach the door or the wall. The patio still falls towards the drain and away from the house, and the drain must connect to a soakaway or surface water drain. Approved Document H sets out where rainwater should go, with a soakaway preferred where the ground allows.
Falls and where water goes
A patio that sits at the right height but falls towards the house still sends water at the wall. We build a fall away from the house, typically around 1 in 60 to 1 in 80, and plan where the water ends up. On the glacial till under Cockerton and Harrowgate Hill water soaks away slowly, so a channel drain is more often needed than on the sand and gravel under Blackwell.
If your garden is near Cocker Beck or the Skerne, check the Environment Agency's flood risk service. Low ground by Cocker Beck in Cockerton is mapped in Flood Zones 2 and 3, and raising ground levels there can push water elsewhere.
Old patios that are too high
Many Darlington homes inherited a patio laid at the wrong level. Signs include:
- damp patches or tide marks on inside walls level with the patio,
- the patio surface within one or two brick courses of the DPC line,
- air bricks partly or fully covered,
- puddles against the house after rain.
The usual fix is to lift the patio, dig down and relay it at the right level, sometimes with a drain along the wall. Patching or sealing the wall rarely cures it.
Listed houses and conservation areas
In Darlington's conservation areas, including West End, Cockerton and Hurworth, a ground-level back-garden patio is normally permitted development. If the house is listed, lowering ground or cutting new steps against historic walls may need listed building consent, so speak to Darlington Borough Council first.
Questions people ask
Can you lay a patio level with the damp-proof course?
No. The finished patio should normally be at least 150mm below the DPC, as Approved Document C expects, to stop splash and ground moisture bridging it.
Is it legal to have a patio less than 150mm below the DPC?
A patio does not usually need building regulations approval, but laying one closer than 150mm risks damp in the house. Where a level threshold is essential, a channel drain against the house is the accepted way to protect it.
My house has no visible damp-proof course. What then?
Assume it sits near internal floor level, keep the patio well below that and away from the wall with a gravel strip or drain. Old cottages may need extra care.
Can a patio cause damp?
Yes, if it is too high, buries air bricks or falls towards the house. Lowering it and correcting the fall usually solves the problem.
Sources: GOV.UK: Approved Document C, resistance to moisture; GOV.UK: Approved Document H, drainage and waste disposal; Darlington Borough Council: conservation areas; Environment Agency: check long-term flood risk.