Soakaway Installation Cost Guide
Honest, typical guide prices for soakaways and drainage fields across Worcestershire and Shropshire — what affects the price, and how to tell when an old soakaway has failed.
How much does a soakaway cost? In short
In Worcestershire and Shropshire a garden or rainwater soakaway typically costs £800 to £1,800 installed, a larger driveway or full-roof soakaway £1,500 to £3,000, and a full drainage field for a septic tank or sewage treatment plant £2,500 to £6,000 or more. A standalone percolation test and soakaway design costs £150 to £300, and is deducted from the job price if we carry out the installation. Ground conditions, size, depth, access and reinstatement are what move a job within those ranges — so we confirm the exact figure with a free site survey and a written quotation.
Typical soakaway installation prices, Worcestershire & Shropshire (guide only)
| Type of soakaway | Typical guide price | What it covers |
|---|---|---|
| Garden / rainwater soakaway | £800 – £1,800 | Crate soakaway for a downpipe, patio or small garden drainage problem, including excavation, crates, membrane and backfill. |
| Driveway / full-roof soakaway | £1,500 – £3,000 | Larger crate system with silt trap and connecting pipework, sized for the run-off from a driveway or an entire roof. |
| Drainage field (septic tank or treatment plant) | £2,500 – £6,000+ | Full BS 6297 drainage field including percolation testing, design, trenching, perforated pipe and gravel. |
| Percolation test & design only | £150 – £300 | Standalone soil testing and soakaway design, deducted from the job price if we carry out the installation. |
What Is a Soakaway?
A soakaway is an underground structure that collects water and lets it drain away naturally into the surrounding soil. Traditionally a pit filled with rubble, modern soakaways use plastic crate systems wrapped in a permeable membrane, which store far more water in a smaller excavation and resist silting up for decades.
There are two main types. A surface-water soakaway takes rainwater from roofs, driveways and patios, keeping it off the mains sewer and out of your garden. A drainage field (sometimes called a foul soakaway) is a network of perforated pipes laid in gravel trenches that disperses the liquid effluent from a septic tank or sewage treatment plant, letting the soil provide the final stage of treatment.
When Do You Need a Soakaway?
Building Regulations (Part H) treat a soakaway as the preferred destination for rainwater on new builds and extensions — connecting new surface water to the foul sewer is generally not permitted. Planning conditions on new driveways and paved areas often require one too, so that run-off is managed on your own land.
For off-mains properties, the Environment Agency General Binding Rules mean a septic tank must discharge to a properly designed drainage field, not to a ditch or stream. Any new drainage field must be designed to BS 6297 and sized using a percolation test — timed test holes that measure how fast water drains through your soil. Without a valid percolation test, Building Control will not sign the work off, and an unsized soakaway is one of the most common causes of early failure we see.
Typical Soakaway Installation Prices
Every site is different, so treat the figures below as typical guide prices for Worcestershire and Shropshire rather than fixed quotes. We always confirm the exact price with a free site survey and a written quotation before any work starts.
Garden / Rainwater Soakaway
£800 – £1,800
Crate soakaway for a downpipe, patio or small garden drainage problem, including excavation, crates, membrane and backfill.
Driveway / Full-Roof Soakaway
£1,500 – £3,000
Larger crate system with silt trap and connecting pipework, sized for the run-off from a driveway or an entire roof.
Drainage Field for a Septic Tank or Treatment Plant
£2,500 – £6,000+
Full BS 6297 drainage field including percolation testing, design, trenching, perforated pipe and gravel. Larger households and slow-draining ground sit at the top of the range.
Percolation Test & Design
£150 – £300
Standalone soil testing and soakaway design. Deducted from the job price if we go on to carry out the installation.
What Affects the Cost of a Soakaway?
Ground conditions — free-draining sandy soil needs a smaller, shallower soakaway; slow-draining ground needs a bigger one, and sometimes a different solution entirely.
Size and depth — the area being drained (roof size, paved area or household occupancy) and the depth to suitable soil directly set the amount of excavation and materials.
Access — a rear garden only reachable through the house means smaller machines or hand digging, which adds labour time and spoil-removal cost.
Distance and levels — regulations require soakaways to be at least 5 metres from buildings and boundaries, so long pipe runs or awkward falls can add to the price.
Reinstatement — relaying a driveway or patio above the pipe route costs more than trenching through a lawn.
Why Clay Soil Matters in Worcestershire & Shropshire
Much of our region sits on heavy clay — Mercia Mudstone across the Severn and Teme valleys and clay-rich ground through large parts of south Shropshire. Clay holds water instead of letting it drain, which is exactly what a soakaway does not want. On clay sites a percolation test is not a formality; it decides whether a soakaway is viable at all.
Where the clay is workable, the answer is usually a larger or deeper soakaway that reaches better-draining ground. Where it is not, we will say so honestly and recommend an alternative — a drainage mound, a land-drain scheme, or a sewage treatment plant discharging to a watercourse with the appropriate consent. It is far cheaper to find this out from a £150 test than from a failed £3,000 soakaway.
Signs Your Old Soakaway Has Failed
Waterlogged or boggy patches of lawn that never dry out, especially over or downhill of the soakaway.
Gullies and downpipes overflowing during ordinary rain, not just storms.
A septic tank that needs emptying far more often than it used to, or sewage smells around the drainage field.
Slow-draining toilets and sinks across the whole property with no single blockage found.
Old rubble soakaways silt up and cannot usually be cleared — replacement with a modern crate system or new drainage field is almost always the right fix.
Soakaway Cost FAQs
Quick answers to the questions homeowners across Worcestershire and Shropshire ask us most.
How much does a soakaway cost to install in the UK?
As a typical guide, a garden or rainwater soakaway using modern crate systems usually costs between £800 and £1,800 installed. A larger surface-water soakaway serving a driveway or full roof area is typically £1,500 to £3,000. A full drainage field for a septic tank or sewage treatment plant generally ranges from £2,500 to £6,000 or more depending on size and ground conditions. Every site is different, so we always confirm prices with a free site survey and written quotation.
Do I need planning permission for a soakaway?
A soakaway on its own rarely needs planning permission, but the work usually falls under Building Regulations. Part H of the Building Regulations covers rainwater and foul drainage, and drainage fields for septic tanks must also meet the Environment Agency General Binding Rules and BS 6297 design standards. If the soakaway is part of a new build or extension, it will be checked by Building Control. We handle the compliance side for you on every installation.
What is a percolation test and why do I need one?
A percolation test measures how quickly water drains through your soil. Test holes are dug, filled with water and timed as they empty. The results determine whether a soakaway will work at all on your ground and, if so, how large it needs to be. Building Control and the Environment Agency expect percolation test results for any new drainage field, and a soakaway sized without one is a common cause of early failure.
Can you install a soakaway in clay soil?
Sometimes, but not always. Heavy clay drains very slowly, and much of Worcestershire and parts of Shropshire sit on clay-rich ground. If a percolation test shows the clay is too impermeable, a standard soakaway will simply fill up and flood. In that case the alternatives are a larger or deeper design that reaches better-draining ground, a drainage mound, or discharging treated water elsewhere, for example from a sewage treatment plant to a watercourse with consent. We will always tell you honestly if a soakaway is not the right answer for your ground.
How long does a soakaway last?
A well-designed modern crate soakaway in suitable ground should last 20 to 50 years. Older rubble-filled soakaways tend to silt up much sooner, often within 10 to 15 years. Drainage fields serving septic tanks last longest when the tank is emptied regularly, as this stops solids washing through and clogging the pipework. If your soakaway is repeatedly backing up, it has usually reached the end of its life and needs replacing rather than clearing.
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