Most Walthamstow driveways don't need a soakaway or an attenuation tank at all, provided the surface itself lets water through. Where they are needed depends on three things: the paving you choose, the ground under your front garden, and how close the drive sits to your house. Here is how to work out which one applies to your property.
If you are paving more than 5 square metres of a front garden with an impermeable surface, such as standard block paving on a compacted sub-base, tarmac or plain concrete, you need planning permission unless the rainwater drains onto a permeable area within your property. Running it straight onto the pavement or into the road gully isn't allowed.
That's why drainage questions come up so often on Walthamstow driveways. On a typical Victorian or Edwardian terrace off Hoe Street, Forest Road or around the Village, the front garden is small and often slopes towards the house or the footpath. That leaves you three realistic options:
A soakaway is an underground chamber, usually made of plastic crates wrapped in geotextile, that holds rainwater and lets it seep into the surrounding soil. It only works if the ground will actually absorb water. Walthamstow's ground varies. Some areas sit on river terrace gravels, which drain reasonably well, but large parts of the borough are on London Clay, which hardly drains at all. Two streets apart can give very different results.
The only reliable way to know is a percolation test, carried out to the BRE 365 method: dig a trial pit, fill it with water and time how fast it drains. Building Regulations guidance also says a soakaway should be at least 5 metres from any building, and on a short terraced front garden that alone can rule it out.
If the test passes and you have room, a soakaway for a typical single or double driveway is usually a modest job, often somewhere around £800 to £2,500 installed. The final figure depends on the size, how deep you have to dig and how easy access is.
If your ground is clay, or there isn't space to keep a soakaway 5 metres from the house, an attenuation tank is the usual fallback. It stores the water during heavy rain and releases it slowly through a flow control into the surface water or combined sewer, which eases the pressure on the local drainage network during storms.
This is a bigger job. You will normally need permission from Thames Water to connect to the public sewer, plus a new connection or the use of an existing one, and the tank needs a sensible inspection point. Depending on size, depth and how far it is to the sewer, budgets of £2,500 to £6,000 or more are realistic. Waltham Forest has known surface water flooding hotspots, so if your property sits in one, slowing down run off is worth doing anyway.
For most front driveways in Walthamstow, a properly built permeable surface avoids the problem altogether. The open graded sub-base underneath acts as a storage layer in its own right, so water is held and released into the ground gradually. On heavy clay a contractor may add a perforated pipe at the bottom of the sub-base leading to a small overflow, but that is still far simpler than a separate tank.
The catch is that permeable paving has to be built correctly. Laying permeable blocks on a standard Type 1 sub-base, which many cheaper installers do, defeats the point and can leave puddles within a year.
A bit of checking at the start saves money and arguments later.
No. Rainwater from a new impermeable driveway must not be directed onto the highway, and the council can take action if it is. It needs to go to a permeable area, a soakaway or an approved sewer connection.
It can be, but only if it is laid on a permeable base such as open graded stone or porous asphalt. Resin laid over existing concrete or tarmac is not permeable and needs separate drainage.
Usually not, as long as the property is a house rather than a flat, isn't listed and isn't in an area with extra restrictions. Parts of Walthamstow, including the Village, are conservation areas, so check with Waltham Forest Council first.
40 Brentham Way, London, W5 1BE
Enquiries answered within one working day.