Channel drains, ACO drains & threshold drainage
In short
A linear channel set across a threshold or at the low point of a drive, catching run-off before it reaches a garage, a doorway or the pavement. Simple, effective and cheap when it goes in with the drive — considerably less so when it is cut in afterwards.
Also called: ACO drain · Linear drain driveway · Slot drain · Drainage channel across driveway
Signs you need this
- Water going under a garage door or over a doorstep in heavy rain
- A drive that falls towards the house rather than away from it
- Run-off from the drive crossing the pavement into the road
- An existing channel that fills and overflows
- A grating that has cracked, sunk or rocks under a wheel
- A drive at the bottom of a slope collecting run-off from above
A channel drain is a length of pre-formed channel with a grating over it, bedded in concrete flush with the surface and connected to an outfall. It intercepts water running across the drive along its whole length rather than at a single point, which is why it is the right answer at a threshold: a garage door is a three-metre-wide problem and a single gully at one end of it is not a three-metre-wide solution.
The two places it earns its keep are a garage or door threshold on a drive that falls towards the building, and the bottom of a drive that falls towards the highway. Both are situations where a large area of hard surface is delivering water to a line rather than a point. Between them they account for the overwhelming majority of channel drains on domestic drives, and both are cheapest by a wide margin when they are designed into a new drive.
Getting one right is mostly about three things. The channel has to be bedded in concrete with proper haunching, because a channel set in sand rocks and cracks under a wheel. It has to be set marginally below the finished surface so water actually enters it rather than running over the top. And the grating has to be rated for what will drive over it — a light domestic grating in a drive that takes a delivery van will fail, and the load classes are there to be specified rather than guessed at.
The outfall is the part that gets least attention and causes most of the failures. A channel is only as good as where it discharges to, and running one into an undersized soakaway, a silted-up gully or — worst of all — a foul drain simply moves the problem. The connection wants sizing for the catchment, the fall wants to be positive along its length, and it wants a silt trap or an accessible cleaning point so it can actually be maintained.
Maintenance is genuinely required and genuinely simple. Gratings lift out, and the channel underneath collects leaves, grit and silt. Cleared twice a year — before autumn and after — a channel drain works indefinitely. Left for a decade it silts up solid, and the first anyone knows about it is water going under the garage door during a downpour. That is the commonest reason an existing channel appears not to work.
Retrofitting one into an existing drive is entirely possible but it is real work, not a bolt-on. The surface has to be cut and broken out along the line, the trench dug, the channel bedded and connected to a genuine outfall, and the surface reinstated — which on tarmac, resin or imprinted concrete leaves a visible line for good. It is another argument for getting the drainage right when a drive is being built rather than discovering the problem the following winter.
What the job covers
- The catchment worked out so the channel and outfall are sized properly
- Channel bedded and haunched in concrete, never in sand
- Set marginally below finished level so water actually enters it
- Grating specified to the correct load class for the traffic
- Positive fall along the channel to the outlet
- Connection to a genuine outfall — never to a foul drain
- Silt trap or accessible cleaning point so it can be maintained
- Surface reinstated neatly where a channel is retrofitted
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your contractor has to honour it. On driveways it would also be close to meaningless: the groundworks are usually the biggest single factor, and how deep the dig has to go varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Where should a channel drain go?
Across the threshold it is protecting — a garage door, a doorway — or at the low point of the drive, usually just inside the boundary where it stops run-off reaching the pavement. It should run the full width of the problem: a wide garage opening needs a wide channel, not a single gully at one end of it.
My channel drain overflows. What is wrong?
Usually one of three things: it is silted up and has never been cleaned, the outfall it discharges to is blocked or undersized, or the channel was never big enough for the area draining to it. The first is fixed in an afternoon and is by far the most common. The other two are design problems and need the outfall looking at.
Can a channel drain be added to an existing drive?
Yes, though it is a proper job rather than a bolt-on — the surface is cut and broken out, the trench dug, the channel bedded in concrete and connected to an outfall, and the surface reinstated. On block paving that reinstatement is invisible. On tarmac, resin or imprinted concrete it leaves a permanent visible line.
How often does it need cleaning?
Twice a year is plenty for most drives — before the leaves come down and again afterwards. The gratings lift out and the channel underneath is cleared of silt and debris. It takes minutes and it is the difference between a drain that works for decades and one that quietly stops working after five years.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local contractor — one call back, usually the same day. Free quote, no obligation.