HOW MUCH DOES IT COST TO BUILD A SOAKAWAY?

Written by Daniel Woodley. Fact Checked by Paul Farley. Published to Prices. Updated: 4th March 2023.

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This guide refers to rainwater soakaways and not septic drainage.

A rainwater soakaway is essentially a hole in the ground that collects rainwater from driveways, patios and roof gutters etc. As the hole fills up, the water gradually seeps through the soil beneath and into the water table.

The purpose of this soakaway is to temporarily store rainwater that could otherwise lead to surface flooding or the overwhelming of sewer systems.

Domestic soakaways are usually found under flower beds, lawns or driveways and patios.

Since 2008, all newly constructed driveways must have rainwater management in place; no new driveway should allow rainwater to drain onto the public footpath or highway.

A soakaway is one of several drainage options for driveways, roofs and gardens in general.

In this soakaway guide, we’ll look at:

• How much work is involved with installing a new soakaway.
• Which materials are used.
• How long it takes to build a soakaway.

Also, I’ve published two price examples; one for a straightforward soakaway installation and the second for a more complex project.

+ I’ll point you in the right direction so you can get a custom quote.

Typical soakaway project. Materials by Core Landscape Products.

How is a Soakaway Constructed?

I have over 18 years of experience in the construction and home improvement industries, and this guide is based on my knowledge.

The first step is crucial; one must determine if the ground conditions allow for a soakaway to work.

I’ve worked on projects before where the soil in the garden was made from heavy clay and after digging a test hole, it was clear that the rainwater would take so long to soak away, it would be pointless to construct a soakaway.

Also, if the property is in a low area, the garden could be close to the water table, making the project unviable. Imagine digging a 1-metre hole in a pond, it would quickly fill up with water, and nothing would drain away. The same thing happens to soakaways constructed into the groundwater level.

Here’s how I would test the soil:

Step 1 – First I would dig a small hole 300mm wide x 800mm deep and fill it with water. I would measure the speed at which the water seeps into the ground to determine the percolation rate.

Step 2 – The second method is where I would dig a test hole 1.2 metres deep, cover it and leave it for 48 hours. If on inspection, the hole has filled with water, I’ll know it will never function as a soakaway.

The soakaway construction can begin assuming the test holes prove the project is viable.

Materials List

All of the domestic soakaway projects I’ve worked on required the following materials:

• Hollow plastic crates that contain a large enough void to hold water but are strong enough to stop the hole from collapsing in on itself.
• A geotextile membrane (mesh) to stop soil from blocking the void.
• Pipework to transfer the rainwater from the gutters, driveway, patio etc, to the soakaway.

Based on my experience and the current sale price of these materials I feel that the cost of the soakaway 5 metres from a property will cost between £250 – £350.

The images below help to explain what these materials are and why they’re needed:

Drainage pipe bend

Gravel placed under the soakaway

Example Prices

Even though I’ve built and repaired several soakaways in the past, I asked 29 landscape gardeners and drainage firms from various locations around the UK to give me quotes for a new soakaway.

Quote 1 was for a straightforward project in a lawn with good access. It doesn’t get much simpler than this; dig a hole, a trench and lay the materials in place before backfilling with soil and some grass seed to finish off.

Quote 2 involves lifting sections of a driveway and path, installing the soakaway to a deeper level to bypass the clay soil and finishing off by re-laying the sections of the driveway. This is a more complex project, and the extra costs reflect the difficulty in lifting sections of a driveway and the deeper hole.

If you’re looking for a guide to how much a soakaway costs, use my figures as a better-than-ballpark price but note the following:

• All the figures displayed below include VAT where applicable.
• A percolation test is done by the company prior to the work starting.
• 5 x soakaway crates included (that’s enough for a 60 sq mtr driveway as an example)
• Prices include the purchase and collection of all pipework, filtration membrane, gravel etc.
• Excavation of the ground for the pipe and the hole for the soakaway crates.
• Laying of pipe/crates membrane and gravel etc.
• Re-laying of soil/grass seed and for the second quote, the driveway surface and base layers.
• All waste material is taken away and disposed of.

Soakaway Price 1: In a Lawn or Flowerbed

A soakaway installed under a lawn or flowerbed, some pipework and backfilling.

No tree roots, no concrete, no tarmac, or anything other than soil to excavate.

This is a fairly easy project to undertake:

Soakaway Cost 2: Under a Driveway

This is a more complex project and requires reinforced crates that will hold the weight of the vehicles; extra depth is required due to the presence of clay soils near the surface.

Sections of the driveway need to be pulled up for the trench and the hole; this will need to be “made good” afterwards.

This isn’t a project that can be completed in half a day; it’s disruptive and requires extra materials and labour.

How Long Does it Take to Install a Soakaway?

When I worked as a project manager, I saw projects completed in a morning, but I also saw complex projects with lots of pipework take two days.

I would be surprised if a single domestic soakaway project took more than two days, but it’s possible, depending on the surface type and amount of pipework needed.

The length of the pipe trench also affects the timescale – a five-metre long and shallow pipe trench won’t take long to dig out, while a twenty-five-metre long and much deeper trench would. Again, it all depends on what the worker is digging through and how many pipes need to be connected to the soakaway.

As a broad estimate, I believe it will take between half a day and two days to install a domestic soakaway, connect the pipework and make the surface good.

These Will Affect The Cost of a Soakaway Installation:

The price guide is for typical domestic soakaway installations. You’ll pay a different amount if:

The soakaway is bigger – needless to say, the bigger the soakaway, the more it will cost. The photo below gives you an idea of how gigantic soakaways can be:

Image from Gutter Supplies.

The surface material – I cannot emphasize enough how much the surface material affects the price. Digging a 2-metre-deep hole in a lawn is easy and takes very little time with a mini-digger. The same hole (and trench) through solid concrete, perhaps under steps etc, is completely different.

As part of another project – If you need a soakaway and most of the groundwork has already been completed, then the price may be less than the figures I’ve provided. For example, if you’re having a new driveway installed, then you don’t need to pay twice for the old drive to be excavated, and you don’t pay twice for the new driveway to be laid.

What Type of Tradesperson/Business Installs Soakaway?

Both landscape gardeners and drainage firms install soakaways, but from my experience and the prices I was given, landscape gardeners were cheaper.

Get Your Custom Garden Soakaway Price

Estimates like mine can be helpful for budgeting and are certainly insightful, but the prices are based on examples that may differ from your project.

For projects like soakaways, where the finer details can be the difference between a £500 project and a £5000 one, I suggest you source at least three quotes from local landscape gardeners or drainage experts. 

• Get an accurate price based on the details of your soakaway project.
• A fast service, no chasing disinterested tradespeople, get a price in hours, not weeks.
• Read reviews and feedback from past customers that have been checked and confirmed as legitimate.
• Compare prices online from several firms, all in one place.

Soakaway Question and Answers

Why Trust DIY Gardening

The author of this guide, Daniel, has constructed several rainwater soakaways himself and has also overseen larger installations during his role as a project manager.

As part of his research into prices, Daniel contacted 29 firms and gathered prices from them.

The figures on this page are based on the supplied prices, and we believe they reflect the current going rate for projects like this.

What We Look For When Contacting Firms For Prices

To ensure accuracy, we ask UK based firms to provide us with prices for projects.

We select the firms based on these criteria:

• From several locations around the UK.
• Must have at least 5 years of experience.
• Must be a member of a recognised industry verification program.

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