CLEARMASTERS
in drainage
levels first
Regulations
and reinstate
for aftercare
The basics
What does a soakaway do?
A soakaway takes rainwater from your roof, drive or yard and lets it soak slowly back into the ground, instead of sending it to a sewer or letting it pool and flood.
Once it’s in, a soakaway needs occasional care, so see soakaway maintenance. For sewage rather than rainwater, a septic tank or treatment plant discharges to a drainage field instead.
We do this work across Surrey, West Sussex, East Sussex, Kent, Hampshire and London, with tankers and engineers in each area most days.
The Building Regulations put soakaways first: rainwater should go to a soakaway or other infiltration system where the ground allows, and only to a watercourse or sewer if it doesn’t. So if you’re building an extension or a new drive, a soakaway is often what Building Control will expect to see.
Modern soakaways use plastic crates wrapped in a geotextile membrane. They’re mostly empty space, so they hold far more water than the old rubble-filled pits, and they’re much less likely to silt up.
Step by step
How a crate soakaway is installed
Step through a typical installation, or let it play. Tap a step to jump to it.
Infiltration test calculator
How well does your ground drain?
Soakaways are designed using an infiltration test, usually to BRE Digest 365. A trial pit is dug to the depth the soakaway will be, filled with water, and timed as it drains. It’s filled and timed three times, and the slowest result is used.
The result is the soil’s infiltration rate. Sandy and chalky ground drains quickly; heavy clay can be so slow that a soakaway won’t work at all, and something else is needed.
Enter your pit’s size and the time the water took to fall from 75% to 25% full to see the rate.
Fill the test pit, then time how long the water takes to fall from 75% to 25% of its depth. Repeat three times and use the slowest result.
A guide only. It uses the BRE Digest 365 formula: the volume drained between 75% and 25% full, divided by the pit’s wetted area at half depth and the time taken. A soakaway is then sized from this rate, the area it drains and local rainfall data, which we do as part of the design.
When you need one
When do you need a soakaway?
Any time new roof or paved area is added and the water has to go somewhere. Building Control will want to know where the rainwater from an extension or new building goes, and a soakaway is the first option they’ll look for.
Front gardens are a common one. Since 2008, paving over more than 5 square metres of a front garden in England with a surface that doesn’t let water through needs planning permission, unless the water is directed to a lawn, border or soakaway on your property.
Older rubble soakaways also reach the end of their life. Once they’re full of silt, the only real fix is a new one.
You might need a soakaway if you have
- An extension, garage or outbuilding going up
- A new or replaced driveway or patio
- Water pooling on the lawn after rain
- Downpipes that just spill onto the ground
- An old soakaway that’s silted up and overflowing
Compared
Crate soakaway or rubble soakaway?
| Crate soakaway | Rubble soakaway | |
|---|---|---|
| Storage | Around 95% empty space, so a smaller hole holds more | Around 30% empty space between the stones |
| Silt | Wrapped in membrane, with a silt trap in front | Fills with silt and soil over time |
| Maintenance | Can be inspected and jetted through an access point | Usually can’t be cleaned once it’s blocked |
| Life | Many decades if kept clear of silt | Often fails within a few decades |
| Design | Sized to the infiltration rate and rainfall data | Often dug by guesswork |
Cost
What affects the cost of a soakaway?
We quote after a survey and a percolation test. These are the main things that set the price.
| Factor | Why it matters |
|---|---|
| Area being drained | The bigger the roof or paved area, the more storage the soakaway needs. |
| How fast your ground drains | Slow-draining ground, like clay, needs a bigger soakaway or a different solution. |
| Access and digging | Room for a digger, how far spoil has to go and what’s in the way. |
| Pipework | How far the soakaway is from the downpipes or drains, and any new gullies or channels. |
| Reinstatement | Putting back lawn is cheaper than relaying paving or a drive. |
Why Clearmasters
Why choose Clearmasters?
We don’t just install soakaways, we jet and desilt them too, so we know what makes one last. Every soakaway we build is sized from a proper test, and easy to maintain.
Ask us a questionWe survey before we dig
Levels, ground conditions, buried services and where the water can go, checked before we quote.
Done to the rules
Designed and built to the Building Regulations, British Standards and the manufacturer’s instructions.
We look after it afterwards
We empty, jet, survey and service what we install, so you have one firm for the life of the system.
Built to be maintained
A silt trap and access point, so it can be checked and jetted in years to come.
What our customers say
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Questions answered
Soakaway FAQs
How big does my soakaway need to be?
It depends on the area it drains, how fast your ground drains and the local rainfall. We size it from a percolation test, usually using the BRE Digest 365 method.
How far from my house does a soakaway need to be?
The Building Regulations say soakaways generally shouldn’t be within 5 metres of a building or road, or in unstable ground, so water doesn’t undermine the foundations.
What if my soil is clay?
Clay drains slowly, so a soakaway may need to be much larger, or may not be suitable at all. Then the options include a storage tank with a controlled outflow to a watercourse or sewer. The test will show which.
Can a soakaway take sewage or treatment plant water?
No. Soakaways are for rainwater. Effluent from a septic tank or treatment plant needs a properly designed drainage field.
Do I need planning permission for a soakaway?
Not usually for a domestic soakaway, but the drainage for new buildings and extensions needs Building Regulations approval, and larger or commercial systems may need planning consent.
How long does a soakaway last?
A well-designed crate soakaway with a silt trap can last for many decades. Keeping gutters, gullies and the silt trap clear makes the biggest difference.
What are the signs of a failing soakaway?
Water backing up in gullies or downpipes, pooling over the soakaway and slow drainage after rain. Sometimes jetting and desilting brings it back; if not, it needs replacing.
Got a different question? Call 03333 233566 or send us a message.
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