The Most Important 150mm on the Job: Setting Patio and Driveway Heights Against the House
Photo by Photo by Georg Eiermann on Unsplash on Unsplash
Most paving problems do not announce themselves on installation day. They turn up months later as a damp patch beside the door, a doorstep that feels wrong underfoot, or a puddle that sits exactly where it shouldn’t. By then, the base is compacted, the paving is laid and the only sensible fix is the expensive one.
The detail that decides a lot of this is the point where the new patio or driveway meets the house. It is not glamorous. It rarely makes it into the glossy photos. But get it right at design stage and the rest of the job has a much better chance of behaving itself.
The line you cannot afford to bury
Every house has a damp-proof course — the DPC — running through the wall at roughly skirting-board height. Its job is to stop moisture rising up through the masonry. External ground levels need to stay below it, typically by at least 150mm, which is about two brick courses.
That figure is not a suggestion. Bury the DPC under a raised patio or a new driveway and you have given damp a bridge straight into the wall. The same applies to air bricks. They need to stay clear so the floor structure below can breathe. A nicely laid patio that blocks an air brick is a nicely laid patio that can contribute to timber problems later.
If the existing garden sits high against the house, the answer is usually to dig out rather than build up. It is more work, but it is the honest work. Building up to meet a high garden is how thresholds end up too high, DPCs end up covered and everyone ends up pretending the damp patch is a ventilation issue.
Fall away from the building, not vaguely in that direction
Paving needs a fall so water can run off. For a patio, something around 1:60 to 1:80 is usually sensible. For a driveway, you may need a little more, depending on the surface and the length of the run. The exact figure matters less than the principle: the finished surface should slope away from the house.
This is where “it looks about right” causes trouble. A 3-metre patio at 1:80 falls about 37mm. At 1:60 it falls about 50mm. Those numbers are small enough to be missed by eye and large enough to decide whether water clears the door or collects by the threshold.
Set the fall out properly with a laser level or a string line. Check it at the door, at the far edge and at the drainage point. If the ground naturally slopes towards the house, do not fight it with a token fall. Plan a channel drain or a suitable drainage path before the paving starts.
Steps, thresholds and the trip hazard no one notices until it is dark
A back door threshold is a transition, not just a gap. The paving should sit below the door cill or threshold in a way that lets water run away from the frame. On sliding doors, the track is often low, so the paving needs to sit below it with a sensible step down. On outward-opening doors, check the swing and the clearance before the levels are fixed.
Where a step is needed, make it a proper step. A 150mm rise is comfortable and familiar. A 50mm lip is the sort of thing people miss when carrying a washing basket. It is also the sort of thing that gets blamed on the paving long after the door has been blamed first.
If level access is the aim — for a wheelchair, a pram or simply fewer trips — that needs designing in from the start. It usually means a threshold drain, a very carefully set fall and a clear drainage path. It does not mean laying paving level with the door and hoping for the best.
Water needs somewhere to go
A fall only works if it leads somewhere useful. That could be a soakaway, a gully, a channel drain or a permeable surface with the right sub-base beneath it. What it should not be is a vague hope that the water will disappear into the lawn.
On tighter sites, a linear channel drain across the doorway is often the cleanest solution. It catches water before it reaches the threshold and sends it to a suitable outlet. On larger patios, the fall can run to a planted edge or a drainage channel, provided the levels are worked out properly. On driveways, check where the water will go before it reaches the pavement or a neighbour’s boundary. Drainage is one of those things that is much easier to plan than to retrofit.
It is also worth checking existing gullies and drainage connections before work starts. A new patio that sends water to a blocked or unsuitable drain is not a drainage solution. It is a delay.
Where this goes wrong on real jobs
The common story is simple. The garden is a bit high. The old patio was a bit low. Someone decides to “bring it up to door level” because it looks neater. The DPC gets covered, the air brick gets hidden and the fall runs back towards the house because the far edge is higher than the door.
A few months later, there is a damp smell in the back room, a stain on the render and a doorstep that holds water. Lifting and relaying the patio is now the cheap option compared with ignoring it. That is before anyone has discussed the cost of replacing a door frame or dealing with damp inside.
The frustrating part is that none of this is exotic. It is basic setting out. It just needs to be decided before the sub-base goes down.
A design-stage checklist for the back door
Before any paving is ordered, write down the finished level at the door, the DPC height, the air brick positions and the direction of fall. Check the door threshold and the step height. Decide where the water will go and how it will get there. Mark the drainage on the plan, not just in someone’s head.
Then check it again when the ground is excavated. Existing levels have a habit of changing once the old surface comes up. The back door is where all these decisions meet, and it is much easier to have that conversation with a level and a plan than with a damp patch and a bill.
If you are planning a patio or driveway in 2026, start at the house. The rest of the job follows from there.
