How Much Does a Soakaway Cost in 2026?
A standard crate soakaway costs £1,500 to £4,000 to install. A small garden soakaway starts at £600, while a large soakaway for a driveway or big roof can reach £5,000. Most jobs also need a percolation test first, which costs £200 to £500. Here is what a soakaway really costs and how to keep the bill down.
£600
Garden soakaway from
£1,500+
Standard soakaway
Up to £5,000
Driveway soakaway
£200–£500
Percolation test
Prices updated June 2026 · Based on industry data and contractor submissions.
A soakaway must be at least 5 metres from any building. Surface water drainage is covered by Building Regulations Approved Document H, which sets the distance rule and the percolation test used to size the pit. Read the official gov.uk drainage guidance (Part H) before any work starts.
Soakaway Prices at a Glance
How much does a soakaway cost? These are typical UK prices for the most common jobs, from a small garden soakaway to a large driveway one, plus the percolation test that comes first and the cost of replacing one that has failed.
Small garden soakaway
Supply and install for a patio, shed, or small roof
£1,000
£600 – £1,500
Standard crate soakaway
Sized for a typical house roof, plastic crates
£2,500
£1,500 – £4,000
Large / driveway soakaway
Big roof area or full driveway surface water
£3,500
£2,000 – £5,000
Percolation test
Ground assessment to size the soakaway
£350
£200 – £500
Replacing a failed soakaway
Dig out and replace a silted or collapsed soakaway
£2,000
£1,000 – £3,000
Prices based on industry data. Actual costs depend on your ground type, the crate volume needed, the depth of the dig, and your location.
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What Drives the Price of a Soakaway
Two soakaways on the same street can cost very different amounts. The biggest factor is your ground. Clay drains slowly and needs a much larger pit to store the same water, while free-draining sand or gravel needs far less. After that, it comes down to the crate volume, the depth and access for the dig, and whether a percolation test is needed first.
| Cost factor | Typical impact |
|---|---|
| Soil and ground type | Big impact |
| Crate storage volume | £60 – £120/crate |
| Depth and excavation | £300 – £1,500 |
| Access for machinery | £200 – £800 |
| Percolation test | £200 – £500 |
| Silt trap / catchpit | £150 – £400 |
Under Building Regulations Approved Document H, a soakaway must sit at least five metres from any building so it does not soften the ground beneath the foundations. The size of the pit is worked out from the percolation test and the area of hard surface draining into it. If your ground has a high water table or is heavy clay, a soakaway may not be allowed at all. You can read the rules in the official gov.uk drainage and waste disposal guidance.
When a Soakaway Is Not Allowed
A soakaway only works if the ground can absorb the water. Sometimes it cannot, and forcing one in is throwing money away. Here is when a soakaway is ruled out, and what your installer will suggest instead.
High water table
If groundwater sits close to the surface, especially in wet weather, the pit fills up and has nowhere to drain. A percolation test in winter usually catches this. The fix is an attenuation tank that holds the water and releases it slowly, or a connection to a surface water sewer.
Heavy clay ground
Clay barely drains, so the soakaway would have to be enormous and would still struggle to keep up. If the percolation test shows the ground drains too slowly, a soakaway is not the answer. Most installers will recommend connecting to a surface water sewer or fitting a slow-release attenuation system instead.
Too close to a building or boundary
Part H requires a soakaway to be at least five metres from any building. On a small plot there may simply not be room to meet that and stay clear of drains and boundaries, in which case an alternative drainage route is needed.
If you are not sure whether you can drain to a soakaway or need to connect elsewhere, your water and sewerage company can tell you what is allowed in your area. Find your provider through Water UK.
Soakaway Costs by Region
Soakaway prices vary by region, mostly down to labour rates and how busy local groundworkers are. These are average costs for a standard crate soakaway, including a percolation test, by area.
| Region | Average Cost | vs National |
|---|---|---|
| London | £3,100 | +24% |
| South East | £2,850 | +14% |
| East of England | £2,700 | +8% |
| South West | £2,550 | +2% |
| Midlands | £2,500 | Average |
| Yorkshire | £2,250 | -10% |
| North West | £2,200 | -12% |
| North East | £2,100 | -16% |
| Scotland | £2,200 | -12% |
| Wales | £2,200 | -12% |
Based on industry data. Typical standard crate soakaway including a percolation test.
How to Get Your Soakaway for Less
A soakaway is one of those jobs where it is easy to overpay if you do not know what should be included. A few simple steps keep the bill in check.
Get at least 3 quotes from drainage specialists
Soakaway prices vary a lot between firms, especially once a dig and crate volume come into it. A good local groundworker is often much cheaper than a national drainage brand for the same soakaway. Getting three written quotes lets you compare like for like and spot anyone overspecifying the crates. Always ask exactly what is included, because some quotes leave out the percolation test, the silt trap, or reinstating the lawn or driveway over the top.
Do a percolation test before sizing anything
A percolation test costs £200 to £500 and tells you exactly how fast your ground drains, which is what sizes the soakaway. It stops you paying for a soakaway that is far bigger than you need on free-draining ground, or building one that was never going to work on heavy clay. If an installer wants to dig in a soakaway without testing the ground first, ask why. The test is cheap insurance against building the wrong thing.
Combine the soakaway with other groundwork
If you are already having a driveway, patio, or extension built, ask the groundworker to put the soakaway in at the same time. The digger is on site, the ground is open, and reinstatement is already being paid for, so the extra cost is much lower than calling someone back out later. Bundling surface water drainage into a bigger job is one of the simplest ways to keep the soakaway cost down.
Fit a silt trap to avoid replacing it early
A silt trap or catchpit on the inlet costs £150 to £400 and stops grit, leaves, and fine soil washing into the soakaway and clogging it. A blocked soakaway can need digging out and replacing within a few years, which costs £1,000 to £3,000. Spending a little up front on a silt trap, and keeping your gutters and gullies clear, can double or triple how long the soakaway lasts.
Read the quote before you compare on price alone
A £2,500 quote that includes the percolation test, a silt trap, and reinstating the surface is better value than a £2,000 quote that bills those as extras. Ask for a fully itemised written quote covering the test, excavation, crates, silt trap, reinstatement, and VAT. That way the cheapest number on paper is also the cheapest job in reality, and you are not caught out by add-ons halfway through.
Comparing quotes is the simplest way to pay less
Getting three or four quotes and comparing them is how most homeowners avoid overpaying. It takes a couple of minutes, with no obligation.
Get my free quotesWhat to Expect: How a Soakaway Is Installed
From the first ground test to a finished, working soakaway, here is how a typical job runs.
- 1
Percolation test
A small test hole is dug, filled with water, and timed to measure how fast the ground drains. That rate is what sizes the soakaway. If the ground drains too slowly, your installer will recommend an alternative before any digging starts.
- 2
Design and position
The soakaway is sized from the drainage rate and the area of hard surface it serves. It is positioned at least five metres from any building, and clear of boundaries, trees, and other drains, in line with Approved Document H.
- 3
Excavate the pit
The pit is dug to the required depth, usually with a mini-digger, and lined with a permeable geotextile membrane. The membrane lets water out but keeps surrounding soil from washing in and silting the void.
- 4
Install the crates
Modern plastic soakaway crates are stacked in the pit to create the storage volume, wrapped in the membrane, and surrounded with clean stone. Crates hold far more water for their size than the old rubble-filled soakaways.
- 5
Connect and reinstate
The inlet pipe is connected, ideally through a silt trap, the pit is backfilled, and the lawn or driveway over the top is reinstated. A final check confirms water drains away as designed.
Frequently Asked Questions
How much does a soakaway cost to install?
A soakaway costs £600 to £5,000 to install, depending on its size and the ground it goes into. A small garden soakaway to deal with surface water from a patio or shed roof costs £600 to £1,500. A standard crate soakaway for a typical house runs £1,500 to £4,000, and a large soakaway sized for a driveway or a big roof area can reach £5,000. The biggest cost drivers are the volume of crates needed, the depth and ease of the dig, and whether your ground drains freely or needs a much bigger pit.
How big should a soakaway be?
The size depends on the area of hard surface draining into it and how fast your soil absorbs water. Free-draining sandy or gravelly ground needs a much smaller soakaway than heavy clay, which barely drains at all. As a rough guide, a soakaway for a standard house roof needs around 1 to 2 cubic metres of crate storage, but the only reliable way to size it is to do a percolation test and work it out under Building Regulations Approved Document H. An undersized soakaway floods and fails, so it is worth getting the calculation right rather than guessing.
Do I need a percolation test for a soakaway?
Yes, for any soakaway that is part of a Building Regulations job you should have a percolation test first. The test digs a small hole, fills it with water, and times how quickly the water drains away. That drainage rate is what sizes the soakaway. A percolation test costs £200 to £500 and is money well spent, because building a soakaway in ground that does not drain is a waste of the whole job. If the test shows the ground drains too slowly, your installer will recommend an alternative such as connecting to a surface water sewer or fitting an attenuation system.
Do I need building regulations or planning permission for a soakaway?
A soakaway for surface water usually falls under Building Regulations rather than planning permission. The rules are set out in Approved Document H, which covers drainage and the percolation test used to size the pit. The key requirement most people trip over is the distance rule: a soakaway must be at least five metres from any building so it does not soften the ground under the foundations. Planning permission is rarely needed for a domestic surface water soakaway, but always check with your local council if the work is near a boundary, a watercourse, or a listed building.
How long does a soakaway last?
A well built modern crate soakaway should last 20 to 30 years or more. The crates themselves do not wear out, so what shortens a soakaway's life is silt and debris washing in and clogging the gaps between the crates and the surrounding stone. Fitting a silt trap or catchpit on the inlet, and keeping gutters and gullies clear, makes a big difference. An old-fashioned rubble-filled soakaway tends to silt up far faster, which is why so many older ones need replacing.
Why has my soakaway stopped working?
The usual reason a soakaway stops working is silting up. Over the years, fine soil, leaves, and grit wash in and fill the voids the water is meant to drain into, so the pit can no longer take the flow and water backs up to the surface. Other common causes are an undersized soakaway that was never big enough, a rising water table in wet weather, or heavy clay ground that drains too slowly to keep up. Replacing a failed or silted soakaway costs £1,000 to £3,000, and fitting a silt trap at the same time stops it happening again so quickly.
Reviewed by Chris Ward, Less.co.uk Home Improvement Costs Specialist
Last updated: · Pricing based on industry data and verified contractor submissions · Methodology
