Soakaway Crates Installation: Step by Step How-To & When to Use Them

When to Use and How to Install Soakaway Crates

If you’ve got a standing water problem, you may have heard about soakaway crates – or, as they’re sometimes called; attenuation cells or soakaways.

Soakaway systems are an extremely effective way of dispersing water, without the need for planning complex draining routes or potentially widespread works. However, it’s important soakaway crates are installed correctly, otherwise you may not get the result you’re hoping for.

In this guide, we’ll answer some important questions, including:

  • What exactly is a soakaway crate?
  • When should a soakaway structure be used?
  • How can you install soakaways yourself?
  • Which products will offer a balance of value and performance?

What is a Soakaway Crate System?

Standing water and water infiltration are age-old problems – as are many of the techniques used to deal with the issue.

A traditional standing water solution involves digging a large pit; which is then filled with hardcore, stones and coarse gravel. While immediately effective, this solution is fairly short-lived. The sediment carried by the draining water fills the drainage spaces the less-porous materials create – so, in time, the pit becomes ineffective, the standing water returns – and there’s an increased amount of hard work then involved with re-excavating the area.

Soakaways do away with these issues almost entirely.

A soakaway crate (named because of their resemblance to old milk crates) is simply installed, extremely tough, can carry a significant load, and is designed to never become clogged or ineffective. These crates, or attenuation cells, now feature in an increasing number of building projects – but can be installed yourself.

When Should You Use Soakaway Crates?

Soakaway crates can be used on virtually any site which would benefit from localised water infiltration such as under roads, car parks, pavements and in shopping centres or sports stadiums.

The location of your soakaways is key to its effective performance. Sandy or loamy soils are ideal for soakaways – but you’ll probably need to look into alternatives if you’re up against a heavy clay soil – as the clay will prevent water draining any further.

Assuming you’re looking to take water away from a structure, your ideal site will be lower than that building – or at least on the same level. Soakaway crates should always be at least 5m (16ft) away from building foundations too – to avoid compromising the structure over time.

Assuming your project meets these criteria, soakaways are likely to be the answer you’ve been looking for.

Soakaway Crates and Climate Change

Climate change is the most likely cause of increases in the overall volume and intensity of rainfall in the UK. As the overall average air temperature increases, so does the atmosphere’s ability to hold moisture; just think of what it’s like in a tropical rain forest! Greater volumes of water vapour in the air leads to more intense rainfall episodes which can result in increased water run-off, especially on hard surfaces. If not dealt with properly, localised flooding will occur. Scientists on the whole are predicting an increase in extreme weather including flooding in the UK for the foreseeable future.

Soakaway crates are one element which can help provide resilience to climate change by protecting our towns and cities against flooding. Long-term, they can provide a very cost-effective solution to flood prevention and reduction, helping to protect the built environment.

At the March 2018 Flood and Coast Conference, the Environment Agency’s Chief Executive Sir James Bevan said: “every £1 invested in new flood schemes saves the economy £10 in damages avoided.

Components and Options

There are usually only 3 main components required when creating a soakaway system, they are:

  • Soakaway crates / attenuation cells: The main part of your installation and usually sold in 0.8 cubic metres and 1 cubic metre sets. To allow for jobs of all sizes and applications, individual cells are also available in a variety of smaller sizes.
  • Clips: Clips are required to secure crates to one-another. Attenuation cell sets often come complete with clips – but you may need extras, depending on the installation. Clips are generally designed to connect your crates laterally or vertically.
  • Geotextiles: While soakaways will somewhat disperse sediment that could cause blockages, it’s important you wrap soakaway crates in a geotextile membrane. As well as providing keeping your crates effective for longer, they’ll also prevent crate separation and reinforce your installation.

Crates usually come certified to carry either a 20 or 40 tonne load:

  • 20 tonne: Ideal for residential use in gardens, patios, walkways, etc.
  • 40 tonne: Designed for areas which will experience vehicle traffic.

How Many Soakaway Crates do I Need?

How many soakaway crates do I need you ask? Well that will depend on many variables including the amount of space available, the soil type and incoming/outward flow rate. A groundworker or installer should perform a percolation test on the soil to determine the ground conditions. For example, clay-based soil is heavy and can cause water to filter out slowly, rather than soaking away freely. This test will give the area in square metres required.

For residential use the most common size of soakaway is 1 Cubic Metre (1m³), as this is what most Local Authorities seem to specify. A Soakaway Size of 1m³ is sufficient to drain a roof area of approximately 50 square metres under normal conditions. To make things easy, we sell Soakaway crates in 1m3 packs (or close to 1m3 depending on which soakaway crates you chose).

Soakaway crates are modular, meaning they can be stacked on top of – or next to – one another. Each soakaway crate is a different size, therefore the brand you choose can determine how many soakaway crates your system will need. Here at Easymerchant Limited we have a number of soakaway crates for sale.

To work out what size soakaway is required for your property, use the method below to give you an accurate guide. First, you’ll need to calculate the area of the roof that will discharge into the soakaway. This is calculated as follows:

Calculate the roof area by measuring the length of the roof from one end to the other along the eaves. Then measure the width of the gable end, or the hip end, and divide this number by two. Now multiply the two figures together – keep this number written down on a notepad.

Then you must allow for the slope of the roof you need to multiply your roof area figure by the factor shown below, depending upon the pitch of your roof.

Roof Pitch:
20 Degrees x Factor of 1.182
22.5 Degrees x Factor of 1.207
25 Degrees x Factor of 1.233
27.5 Degrees x Factor of 1.260
30 Degrees x Factor of 1.288
32.5 Degrees x Factor of 1.319
35 Degrees x Factor of 1.350
37.5 Degrees x Factor of 1.384
40 Degrees x Factor of 1.419
42.5 Degrees x Factor of 1.459
44 Degrees x Factor of 1.500
47.5 Degrees x Factor of 1.547

Once you have calculated your effective roof area, use the table below to work out how many soakaway crates you need:

Effective Roof Area (Square Metres)
Size of Soakaway Required   (Cubic Metres)
Number of Century 100 Soakaway Crates Required
Number of Polystorm Soakaway Crates Required
25 m²
0.5m³ (500 litres)
30 m²
0.6m³ (600 litres)
40 m²
0.8m³ (800 litres)
50 m²
1.0m³ (1000 litres)
60 m²
1.2m³ (1200 litres)
80 m²
1.6m³ (1600 litres)
100 m²
2.0m³ (2000 litres)

Installation of a Soakaway Crate System

We’ve broken the installation of a 1 cubic metre attenuation cell soakaway down into X steps – with detail around what’s required at each of those points. You will need to adjust excavation and backfill sizes if your crates vary in size.

Step 1:

Before purchasing items and prepping tools, it’s important you assess the impact that your soakaway could have on the surrounding area. If your soakaway is part of an extension or new build property, you may need to seek permission or advice from your local authority.

Step 2:

When you’re happy to proceed, you should mark and begin to carefully excavate your chosen area. If you’re removing turf, carefully dividing and rolling can protect the sections for use later.

Step 3:

For a 1 cubic metre soakaway set you should excavate a hole which is 1.2m square – and 1.6m deep. As you’ll be aware, a hole of this size is difficult to create manually – so hiring a mini-digger will significantly reduce your timescales.

A 1.6 metre depth allows for a 100mm base of sharp sand, offering a robust base for your soakaway crates. The 1.2m square width of your hole also allows for 100mm of gravel side-fill.

Given the uniform nature of the soakaway crates, you should aim to excavate a hole that is straight and square, housing the system neatly and applying pressure evenly across the crates.

Step 4:

Many soakaway installations require just one set of crates – which often come ready assembled. If you’re assembling your system on-site, you’ll reduce the effort required by doing so before the crates are lowered into the excavation.

Secure your soakaway with the appropriate clips in the configuration required.

Step 5:

To prevent your soakaway losing effectiveness over time, you should ensure it’s wrapped in an appropriate geotextile membrane. Doing so will ensure water still disperses – but soil is not washed into the crate voids.

Depending on the pit you’ve created, you can wrap your crates using 2 methods.

1: Wrap the entire system before it enters the pit.

2: Place the membrane over the pit, allowing the weight of the crate to force it into place, securing at the top when entirely surrounded. You should be careful to ensure no gaps are created if you use this method.

Step 6:

Your soakaway can now be connected to the surface water drainage system. This can be done by removing one of the preformed sections that allows for the entry of either a 100mm flexi or 110mm/160mm fixed pipe.

To ensure no sediment leaks into the crate voids, you should make sure the membrane is tucked securely around the drainage pipe.

Step 7:

To secure and finish the job, you should fill the remaining 100mm around the soakaway system sides with a 10mm pea shingle – before applying another 100mm layer of pea shingle to the top of the system.

You should now apply another 350-400mm of soil on top of the upper later of pea shingle, making sure you firmly tamp this later down. Doing so will help counter any settlement and keep your lawn, walkway or finishing layer even.

Choosing the Right Products

While this guide will help you to get the technical aspects of your installation right, there’s no substitute for working with the right materials in the first instance.

Geocell Soakaway Crates, Polypipe Polystorm Soakway Crates and Brett Martin Soakaway Crates are all high-quality soakaway crates that are available in a variety of sizes and configurations here through EasyMerchant. This broad selection have compressive strengths that range between 20-61tonnes per square meter, so will be suitable for everything from domestic to industrial installations.

While selecting the correct crates for the installation is obviously vital, you’ll significantly reduce effectiveness and longevity of your soakaway if it’s not wrapped in the appropriate non-woven geotextile membrane. EasyMerchant’s Terram Geotextile is the ideal addition to your job – boasting filtration capabilities that make it suitable for even industrial grade separation.

Also, you may need some 110mm Underground Sewer Pipe to connect into the soakaway crates, or sometimes land drainage pipe will be required. Both are available here at Easymerchant Limited.

What is the Delivery Lead Time?

Easymerchant Limited carries plenty of stock of these items so you can look forward to speedy delivery. Many areas can enjoy next day delivery for items ordered by 12:00pm, however as a precaution we always ask that you leave 2-3 days for delivery.


Here’s a brief example video showing how to install a one metre cube soakaway using the Geocell crates:


If you have any further questions feel free to contact us either via our chat feature, by email at or by phone on 01371 850 808!


how to install soakaway creates by easymerchant limited polypipe polystorm

10 thoughts on “Soakaway Crates Installation: Step by Step How-To & When to Use Them

  1. TERRENCE says:

    Thanks for the soakaway crates guide I’m going to buy one of the kits. Are the geocell soakaway crates approved?

    • Adam says:

      HI Terrence, yes the geocell soakaway crates are tested and approved for use in the UK for up to 40 tonnes loading.

      ” Modules tested using UKAS calibrated test machine, range 0 – 60 Tons, UDL, loading rate 0.2 kN/m2. Modules tested for long term creep testing for 90 days and new on-going test.”

    • Adam says:

      Hi Simon. Yes we keep 99% of the items listed on EasyMerchant in stock. All of the different soakaway crates are kept in stock 🙂

        • Adam says:

          Hi Will! There’s no exact science to that. Some crates come with an inlet hole. You can install the pipe through the inlet hole either vertically from the top, or in the side in one of the crates at the top of the tank.

          If the crate doesn’t come with an inlet hole then the pipe can be cut and laid over the top of the tank to allow the water to drain inside it.

          Hope that makes sense!

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