Soakaway and drainage installation
Getting surface water away from the house, drive and garden: channel drains, land drains and properly sized soakaways.
Why drainage deserves attention
Standing water is more than an eyesore. Water sitting against a house can attack the brickwork and damp-proof course, water on a drive or patio speeds up frost damage and algae, and waterlogged ground kills lawns and plants. New hard surfaces also have a legal side: a new or replacement front driveway over 5 square metres needs planning permission unless the surface is permeable or the water drains to a permeable area within the property.
Most drainage problems come down to levels and somewhere for the water to go. Getting both right is a groundworks job, and it is cheapest to sort while the drive, patio or extension is being built rather than afterwards.
What a soakaway is and how it works
A soakaway is a pit filled with rubble or, more usually now, plastic crates wrapped in a geotextile membrane. Water from a drain, channel or downpipe is piped into it and soaks away into the surrounding soil. It needs to be sized for the area draining into it, sited away from buildings and boundaries, and the soil has to actually drain: a soakaway in heavy clay can be useless, which is why a percolation test is worth doing first.
For Building Regulations, soakaways for roof or surface water generally need to be at least 5 metres from a building and 2.5 metres from a boundary, though the exact requirement depends on the situation. We size and site them properly rather than digging a token hole.
Channel drains and land drains
A channel drain is the grated linear drain you see across the bottom of a drive or in front of a garage door. It intercepts water running down a slope and pipes it to a soakaway or, where permitted, a surface water sewer. It is the standard fix where a drive slopes towards the house or garage.
A land drain, or French drain, is a perforated pipe in a gravel-filled trench that collects water from waterlogged ground and carries it away. It suits soggy lawns and gardens where water sits after rain. Both rely on a fall to an outfall, so the levels are surveyed before anything is dug.
Drainage with extensions and driveways
Extensions often need drainage work: moving or building over drains needs agreement with the water authority, and new roof areas need somewhere for their water to go. Driveways and patios need falls that shed water away from the house and a planned destination for it. Our driveway drainage guide explains the options for drives in more detail.
Signs of a drainage problem
The obvious sign is water that sits for hours after rain: puddles on the drive, a soggy strip of lawn that never dries, or water pooling against the house. Less obvious signs include green algae spreading across paving, white salt deposits low on brickwork, a musty smell near an air brick, and gullies that overflow in heavy rain. Each points to water that has nowhere to go or is going where it should not.
It is worth acting on these early. Water against a wall over a wet winter can work into the brickwork and the ground under floors, and the longer it goes on the more there is to put right. A site visit identifies where the water is coming from and where it can sensibly be sent.
What affects the cost
Drainage cost depends on how much excavation is needed, the size of the soakaway, the length of pipe runs, the ground conditions and access for a digger. Connecting into an existing system is simpler than building a new one. We assess the levels and the soil at a site visit and give a free written estimate.
Drainage and soakaway questions
- What is involved in installing a soakaway?
- A percolation check on the soil, digging the pit to the right size, fitting crates wrapped in membrane, connecting the incoming pipe, then backfilling. It is sited away from buildings and boundaries and sized for the area draining into it.
- How long does drainage work take?
- A straightforward soakaway or channel drain is usually a short job; longer pipe runs, deep excavation or difficult ground take more time. We give a programme with your estimate.
- What affects the cost of a soakaway?
- The size of the pit and crates, the length of the pipe run, excavation and disposal of spoil, ground conditions and access.
- Will a soakaway work in clay soil?
- Heavy clay drains very slowly, so a standard soakaway may not work. A percolation test tells you before you spend money; alternatives include larger systems or connecting to a surface water sewer where permitted.
- Do I need drainage for a new driveway?
- If the drive is over 5 square metres and at the front, yes: it must be permeable or drain within your property, otherwise planning permission is needed. A channel drain to a soakaway is the usual solution on sloping drives.
Related: driveway drainage guide · foundations and groundworks · block paving driveways · patios, garden walls and driveways.