Soakaway Systems Explained:

Introduction

Spend enough time working around drainage in the UK and you’ll come to a simple conclusion: water doesn’t care what your plans were.

It will find the low point, and it will sit where you don’t want it. If you don’t guide it where to go, it’ll make its own decision—usually somewhere inconvenient.

That’s the job of a soakaway. Not to resist water, but to manage it appropriately.

If its installed correctly, a soakaway will sit underground for years without causing any trouble. If it’s not installed correctly, it turns into a soggy patch, a blocked system, or worse—something you end up digging out and redoing.

What a Soakaway Actually Does

Basically, a soakaway is just a way of returning rainwater back into the ground in a controlled way.

Water from roofs, driveways, or patios is collected, held for a short time, and then allowed to soak into the surrounding soil naturally.

Where people go wrong is assuming it’s just a hole filled with something loose. It isn’t. For a soakaway to work properly, three things need to line up:

• The ground has to drain
• The system has to be sized properly
• It needs to stay free from silt and debris

Miss one of those, and you’ll start seeing problems sooner rather than later.

Why Soakaway Crates Are Now the Standard

Going back some years, soakaways were often built using rubble or pieces of broken brick. You’d dig a hole, fill it up, and hope it held enough water and drained well enough.

Sometimes it did. Often it didn’t.

The problem was inconsistency. You never really knew how much space you had for water, and over time those voids would clog up anyway.

Crate systems changed that.

They’re lightweight plastic units designed to create a large open space underground—usually around 95% empty. That gives a predictable storage volume and a system you can design around.

They’re also quicker to install, easier to handle, and far more reliable. That’s why they’ve replaced traditional methods on most jobs.

How a Crate Soakaway Works 

A crate system does three simple things:

1. It Collects Water

Rainwater comes in from downpipes or drainage channels.

2. It Holds It

The crates store water temporarily during heavier rainfall.

3. It Lets It Soak Away

Water gradually seeps out into the surrounding soil.

The important part is getting the balance right—enough storage to handle heavy rain, and enough drainage so it empties again before the next downpour.

Ground Conditions

You can install the best crate system on the market, but if the ground doesn’t drain, it won’t perform correctly.

This is the part that gets overlooked most.

A Rough Guide to Soil Types

• Sandy or gravelly ground – drains well, ideal
• Loam – generally fine, depends on compaction
• Clay – slow draining, often problematic

Clay is where most issues come from. Water just sits there. In some cases, you can work around it, but in others, a soakaway just isn’t the right solution.

The key is not assuming.

Why a Percolation Test Is Worth Doing

It’s easy to skip this step, especially on smaller jobs. The ground looks alright, so you get on with it.

That’s how soakaways end up failing.

A percolation test tells you how quickly water drains from the soil. It’s not overly complicated but it gives a good picture of the ground performance.

The Basic Process

• Dig a test hole (at least 300mm cube)
• Fill it with water and let it drain completely
• Fill it again and time how long it takes to empty
• Repeat a few times

What you end up with is a drainage rate you can use to size your soakaway properly.

Getting the Size Right

This is where a lot of installations fall short.

Too small, and the system backs up during heavy rain. Too big, and you’ve wasted time, money, and effort.

What Affects Soakaway Size?

• The area you’re draining (roof, driveway, etc.)
• Local rainfall levels
• Ground drainage rate
• The storage capacity of the crates

For smaller domestic jobs, people often work off a rough guide:

Around 1 cubic metre of soakaway per 50m² of roof area (in good ground)

It’s a starting point, not a guarantee. For anything more serious, proper calculations are the way to go. We can run through it with you.

Where You Put It Matters

Positioning a soakaway isn’t something to guess at.

Put it in the wrong place and you can end up causing structural issues to existing buildings.

Rules to Follow

• Keep it at least 5 metres away from buildings
• Stay clear of boundaries (around 2.5 metres)
• Avoid placing it near roads, load-bearing areas or retaining walls
• If possible, install it slightly downhill, let gravity help out where you can

Places to Avoid

• Near trees (roots can interfere)
• Areas with high groundwater
• Poor draining ground

A soakaway should work with the conditions on the site. Don’t make it harder for yourself.

Installing a Soakaway Crate System

The process itself is fairly straightforward—but getting the details right is important.

1. Digging Out

Excavate enough space for the crates and surrounding material. Make sure the base is level.

2. Preparing the Base

Lay a bed of clean stone to create a stable, level surface.

3. Lining the Hole

Install one of our geotextile membranes around the excavation. This stops soil getting into the system while still allowing water out.

4. Installing the Crates

Assemble and position the crates as detailed in your soakaway plan. Keep them stable and properly aligned.

5. Connecting Pipework

Bring in your inlet pipework and include a silt trap upstream to help keep the system free from blockages.

6. Wrapping It Up

Fully wrap the crates with the membrane. Ensure there are no gaps—this is what keeps the system working long-term.

7. Backfilling

Use clean, free-draining materials, like a pea gravel. Compact carefully so you don’t damage the structure.

8. Finishing Off

Reinstate the surface—whether that’s soil, turf, or paving.

The Real Cause of Most Failures: Silt

Here’s something that doesn’t get talked about enough.

Most soakaways don’t fail because of water—they fail because of dirt.

Over time, silt and debris get into the system and clog it up. Once that happens, the water simply has nowhere to go.

How to Avoid It

• Install a silt trap or catch pit
• Keep gutters and channel drains clear
• Use leaf guards where needed

If you keep dirty water out, the system will last much longer.

Load-Bearing Considerations

Not every crate system is designed to take the same amount of weight.

If you’re installing under a driveway or any area with vehicle traffic, you need crates that are rated for that load.

Using the wrong type might hold up for a while—but eventually, it will fail.

Common Mistakes That Cause Problems

Most soakaway issues come down to a handful of avoidable mistakes:

• Skipping the percolation test
• Installing in unsuitable ground
• Undersizing the system
• Poor membrane installation
• No silt management
• Incorrect location
• Using the wrong backfill

Avoid those, and you’re already doing better than a lot of installations out there.

Maintenance

Soakaways are often treated as if they don’t need any attention once installed.

That’s not quite true.

They’re low maintenance—but not no maintenance.

What to Keep an Eye On

• Gutters and downpipes
• Silt traps
• Drainage flow during heavy rain

A bit of upkeep now and then can add years to the life of the system.

When a Soakaway Isn’t the Right Option

Sometimes, the ground just won’t play ball.

If water isn’t draining, forcing a soakaway into the ground won’t fix it.

Alternatives to Consider

• Attenuation systems
• Surface water sewer connections (where allowed)
• Rainwater Harvesters

The right solution depends on the site.

Final Thoughts

A soakaway crate system isn’t complicated—but it does rely on getting the basics right.

Test the ground. Size it properly. Install it carefully and keep it clean.

Do those, and it will do its job for years.