Surface water drainage in London
Every roof, patio and paved garden sheds a surprising amount of water in heavy rain, and all of it has to go somewhere. When it has nowhere to go it sits — puddles across the patio that last for days, a lawn that turns to mud each winter, or water creeping towards a wall it should never reach. Ninja Plumbers deals with that end of drainage: working out where the water is coming from, where it can legitimately go, and putting in the drainage to get it there.
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What this includes
- Standing water on patios, paths and gardens
- Soakaway design and installation
- Channel and linear drainage across driveways and patios
- New gullies and downpipe connections
- Water pooling against a wall or draining into a lightwell
- Existing surface drainage that has stopped coping
Worth knowing first
A little of this might mean you do not need to call us at all — we would still rather you knew it.
What a soakaway actually is
A soakaway is a hole in the ground, dug well away from the building, filled with something that holds a lot of empty space — traditionally stone, now more often a plastic crate arrangement — and wrapped in a membrane before being buried. Water is piped into it, sits in that space instead of on your patio, and soaks away into the surrounding ground over the following hours. There is nothing clever about it. It is simply somewhere for the water to wait.
Soakaways do not suit every site
They only work if the ground around them will actually take water. Heavy clay drains very slowly, a high water table leaves nowhere for it to go, and a soakaway too close to a building is a way of putting water into your own foundations. Where the ground rules one out, the water has to be piped to an existing drain instead — so this gets tested and worked out first rather than assumed.
Paving over the garden without drainage is the usual cause
Front gardens across London have been paved over for parking, and back gardens for terraces and patios. Grass and soil absorb rain; a slab does not. Pave a garden with no drainage and no fall, and the water that used to soak in now runs to the lowest point, which is very often the back door or the base of a wall. Channel drainage across the paving, or a soakaway behind it, is the part that gets left out.
Water pooling against a wall is a damp problem in waiting
Ground that holds water against brickwork, especially where a patio or path has been built up above the damp-proof course, is one of the routine causes of damp inside. Our damp survey and damp proofing pages go into what that does to a wall. Fixing the drainage outside is frequently the actual repair, rather than anything done to the wall itself.
What affects the price
Surface water jobs range from clearing a single gully to building a soakaway in the garden. The price is set by how much water there is, what ground it has to go into and what has to be dug through to get it there.
The area being drained
A small patio sheds far less water than a whole roof plus a paved drive. The bigger the area feeding into the drainage, the longer the channel runs and the larger the soakaway has to be to cope with a heavy storm.
What the ground is like
Much of London sits on clay, which takes water slowly. A soakaway in clay has to be larger than one in gravel, or may not work at all, so the ground is tested first. That testing is part of the job.
Cutting into what is already there
Setting a channel drain into new paving is simple. Cutting one into an existing concrete drive, a resin surface or laid stone, then making good neatly on both sides, takes more time and more materials than people tend to expect.
Where the water can go
Connecting to an existing surface water drain nearby is often simplest. A long run to reach one, or a low spot such as a basement lightwell that sits below any drain and needs a sump and pump, adds considerably to the job.
The price is agreed before any work starts. We take card and cash.
Common questions
What is a soakaway, in plain terms?
A buried void — stone or plastic crates in a membrane — set away from the building, that rainwater is piped into so it can soak gradually into the surrounding ground instead of standing on the surface.
My patio floods every time it rains. What can be done?
Usually a linear or channel drain set into the paving at the low point, taken to a soakaway or an existing surface water drain. Sometimes the paving itself has been laid falling towards the house, in which case that needs correcting too.
Can rainwater just be connected into the foul drain?
Rainwater and foul water are normally kept separate, and whether a connection is permitted depends on the drainage arrangement in your street. We check what is there before connecting anything into it.
The drain is there but the water still stands. Why?
Either it is blocked, or the underground run is damaged — collapsed, cracked or knocked out of line — and the water is not getting away. A camera survey settles which, and our drain repairs page covers the repair side of it.
Do I need permission to pave over my front garden?
In England, paving more than five square metres of a front garden with a surface water cannot soak through needs planning permission, unless the rainwater is directed to a lawn, border or soakaway within the property. Permeable paving, or conventional paving that drains to a planted area, avoids the need. It is worth settling before the paving goes down, because adding drainage afterwards costs more.
How close to the house can a soakaway go?
Building regulations guidance puts a soakaway at least five metres from any building, including next door’s, so the water it releases does not end up softening the ground under foundations. In a typical London back garden that distance is not always available, and then the answer is usually to pipe the water to an existing drain instead of forcing a soakaway into a space too small for it.
More drainage work we take on
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Drain Unblocking
Sinks, toilets and outside drains cleared with proper equipment, not a bottle of chemicals.
More on Drain Unblocking -
Blocked Toilet
A toilet that will not flush away, or one that keeps blocking. Cleared, with the cause explained.
More on Blocked Toilet -
CCTV Drain Surveys
A camera down the drain shows what is actually wrong, rather than guessing from what keeps happening above ground.
More on CCTV Drain Surveys -
Drain Repairs
A drain that is actually broken, not just blocked — repaired by digging it up or, where the run allows, without digging at all.
More on Drain Repairs -
Gutter Repair
Blocked, leaking, sagging and overflowing gutters cleared and repaired, along with the downpipes below them.
More on Gutter Repair
Need surface water drainage in London?
Describe the problem and give us your area, and we’ll tell you the price before anyone starts work.