How to Build a Soak Away System

blog header of how to build a soak away system

A soak away drainage system collects surface water from rainfall in the area and re-disperses it back into the ground at a rate that doesn’t flood the nearby soil – if your property has flooding problems, it can be a great solution. Back in the day, these basically just consisted of a trench with a slope, but we now have products available to us like soakaway crates that massively increase the efficiency of the system.

Here, we’ll go over how to build and install your soakaway system in just a few straightforward steps, explaining the equipment you’ll need and a few tips along the way.

Select the Right Location

For your soakaway to be as efficient as possible, you’ll need to pick the right area for it. It should be at least 5 metres away from your property, and further away than that if the chosen site slopes down toward your property (otherwise you risk damaging the foundations). The area should be clear of any underground services like gas and water mains pipes, drainage pipes, comms cables, or electrical cable ducts. If you’re unsure, contact your local authority planning officer for site plans and building regulations to avoid any disasters.

Additionally, you should carry out a soil percolation test to determine whether the soil on your property is appropriate for a soakaway drainage system. Some soils, such as heavy clay soils, will not work with this kind of drainage.

Dig Out the Site

blog image of digging out soakaway area

You’ll need to dig out a hole based on the size of your soakaway crate, taking into account the base, back fill and side fill you’ll need to be adding as well. The layers of sand you’ll need to place all around the crate are around 15cm, so add that to the dimensions of your crate when digging out the pit. Typically, you’ll need to dig a hole that’s around 110cm wide, 175cm long, and at least 130cm deep (the depth should be greater for soakaways under driveways).

Although you can excavate the site by hand if you choose to. it’s much more efficient to use a mini digger. They’re simple to use and will save you lots of time and effort, plus they’re usually inexpensive to hire.

Add Pre Filter

product picture for easymerchant silt trap with bucket

While fitting a pre filter isn’t completely essential. it will improve the lifespan of your soakaway and help maintain it’s efficiency. For instance, a silt trap is installed before and slightly above your soakaway crate and after the drainage pipe, trapping dirt particles and other waste from the rainwater that flows into it before it enters the crate chamber.

All you have to do to maintain your silt trap is remove and clean out the removable bucket inside every two or three months. If you do this, you can prevent debris from entering your soakaway system and clogging or causing damage, which can even lead to you needing a replacement crate later down the line.

Prepare the Base

After you’ve dug out a trench of the correct size, you should remove any stones, roots and rubble from the base and try to smooth out the bottom of the pit as much as you can. You can then add a layer of sand, levelled out and compacted, about 15cm thick for the crates to rest on.

Install Your Crates

blog image of soakaway crates being installed on top of non woven geotextile membrane

Before you place the crates into the hole, you should line them with geotextile membrane. Much like the silt trap, this will reduce the amount of debris that can enter your soakaway crates and significantly increase the lifespan of your system.

You can then lower your crates into the hole and tape the non woven geotextile membrane around the crates, making sure to cover the pipe entry point and every outward face. You can use wire or cable ties to secure the the crates until the side fill has been implemented to stabilize it further.

Connect the Pipes

Depending on the manufacturer of your crates, your entry points will vary – while some will have knock outs or cut outs, others won’t have an entry point at all, meaning the pipe is butted up to the wall of the crate. When using only one pipe, you should turn the other crates so that the pipe entry areas face into the soakaway, preventing the membrane from sagging into them.

Hold the pipe against the entry point, draw around it and mark the centre. You can then cut across the membrane and fold it back, so that you can push the pipe in by about 15cm. Once the pipe is in, you can tape the excess membrane around it to ensure a tight fit.

Backfill the Soakaway

Your pipes will be supported by the side fill you can now add around the existing structure, consisting of a 15cm layer of shingle or sand. In addition to improving water flow into the crate, the side fill will protect the integrity of the structure against any movement or ground disturbance.

Once the side fill is in place, you can start placing another 15cm layer of gravel or sand on top of the crates, followed by a layer of soil with a minimum depth of 15cm for a garden soakaway system. If the soakaway is in a driveway, you may want to increase this to a minimum of 30cm.

Soakaway Installation Advice

Installing soakaways is fairly straightforward, but it’s always good to make sure you know exactly what you’re doing and what you need for the job. Whether you need more information about building your whole soak away, or just want to know what kind of material you should use for the backfilling, we’re here to help. Just contact us through phone or email (whichever option suits you) and we’ll help you with all your drainage needs.

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