Water pooling in your garden after every downpour isn’t just an inconvenience. Left unchecked, standing water can damage foundations, kill plants, and turn lawns into boggy strips of mud that take weeks to dry out. Around 90% of structural damage to basements in the UK is linked to poor drainage, so getting this right matters more than most homeowners realise.
Two of the most common fixes are French drains and soakaways. They both deal with excess water, but they work in different ways and suit different situations. Choosing the wrong one can leave you with the same puddles you started with, so it’s worth understanding what each system actually does before you commit.
What is a French drain?
A French drain is a trench filled with gravel and a perforated pipe that collects water underground and channels it away from your property. The pipe sits at the bottom of the trench, wrapped in geotextile membrane to stop silt and soil from clogging the holes. Water seeps through the gravel, enters the pipe, and flows along a gentle gradient to a discharge point, which could be a ditch, a storm drain, or a soakaway further down the garden.
The key word there is “gradient.” French drains rely on gravity. Without a slope, the water has nowhere to go, so they need careful planning before installation. For most domestic gardens, the trench sits between 200mm and 600mm deep, though commercial systems can go as deep as six metres depending on the site.
French drains are particularly good at intercepting water that moves through the ground laterally. If you’ve got a slope behind your house and water is creeping towards the foundations after heavy rain, a French drain placed across the path of that flow can catch it before it reaches the building. They’re also a solid option alongside retaining walls, where hydrostatic pressure from trapped water can cause cracking and structural movement over time.
What is a soakaway?
A soakaway takes a different approach. Instead of redirecting water somewhere else, it holds it in a contained pit and lets it percolate slowly into the surrounding soil. Older soakaways were simple holes filled with rubble and broken bricks, but modern systems use stacked plastic crates wrapped in geotextile fabric. These crates create a large void underground that fills with water during heavy rain and releases it gradually over hours or days.
Soakaways are designed for surface water, the kind that runs off roofs, driveways, patios, and other hard surfaces. When rain hits an impermeable surface and has nowhere to soak in naturally, a soakaway gives it a controlled route back into the ground. That’s why they’re such a common requirement on new builds and extensions where hard landscaping has replaced soil and grass.
Building Regulations Part H in England and Wales (and equivalent standards in Scotland) often require soakaways for properties where surface water can’t connect to an existing drain or watercourse. If you’re planning a new driveway or patio, your local Building Control officer may ask for a soakaway design as part of the approval process.
The main differences
The simplest way to think about it: a French drain moves water away, and a soakaway stores water until the ground absorbs it.
French drains deal with groundwater and subsurface water. They intercept water that’s already in the soil and redirect it before it causes damage. Soakaways deal with surface water. They collect rainwater runoff from hard surfaces and return it to the earth in a controlled way.
There’s a practical difference in how they’re built, too. A French drain is a long, linear trench that follows the contour of the problem area and needs a consistent downhill gradient. A soakaway is a single, concentrated pit, usually positioned at the lowest point of a drainage run. French drains need somewhere to discharge their water. Soakaways are the destination.
That last point is worth remembering, because the two systems often work together. A French drain collects and channels water along a trench, and a soakaway at the end of the run absorbs it into the ground. It’s not always a question of one or the other.
When a French drain is the better option
French drains work best when you’re dealing with water that’s already underground and moving through the soil towards your property. Common scenarios include:
- A garden on a slope where water runs downhill towards the house after heavy rain
- Persistent damp patches on a lawn that won’t dry out, even in summer
- Retaining walls that are bowing or cracking from water pressure behind them
- Properties at the bottom of a hill where neighbouring land drains towards your boundary
If water is reaching your foundations or causing damp in a cellar, a French drain positioned between the water source and the building can intercept it before it arrives. They also suit long, narrow problem areas like the edges of driveways or paths where water collects against a wall.
When a soakaway makes more sense
Soakaways are the right call when surface water has nowhere to go. If you’ve paved over a front garden for parking, extended a patio, or added a large shed with a roof, the rainfall that used to soak into the soil now runs off and pools instead. A soakaway collects that runoff and lets it drain away underground.
They’re also the standard solution when Building Regulations require you to manage surface water on your own property. If your home isn’t connected to a surface water sewer, or your council won’t allow a new connection, a soakaway is usually the required alternative. Planning applications for extensions and driveways frequently come back with conditions requiring a soakaway to be installed before work can begin.
One thing to check before committing to a soakaway: your soil needs to be able to absorb water at a reasonable rate. A percolation test measures how quickly water drains through the soil on your property. If the ground is heavy clay, water may sit in the soakaway for far too long, and you’ll need an alternative approach or additional measures like a larger crate system or a connection to a watercourse.
Can you use both together?
Yes, and it’s actually one of the most effective setups for properties with multiple drainage issues. A French drain runs along the problem area, collecting subsurface water and channelling it through a perforated pipe to a soakaway positioned at a low point in the garden. The soakaway then absorbs the collected water gradually.
This combined approach is common in gardens where a slope sends groundwater towards the house while surface water from patios and paths needs managing at the same time. A CCTV drain survey can help identify exactly where water is coming from and whether your existing drainage is connected properly, before you start digging.
What about costs?
Costs vary depending on the size of the system, ground conditions, and whether you’re hiring a contractor or doing it yourself. As a rough guide for UK homeowners in 2026:
A French drain typically costs between £45 and £90 per linear metre for materials alone. With professional installation, that rises to around £200 per metre when you factor in labour, excavation, and disposal. A 10-metre French drain across the back of a garden might come in between £2,000 and £3,000 installed.
A soakaway using modern plastic crates usually costs between £1,500 and £2,500 for the system and installation. Rubble-filled soakaways are cheaper at around £1,000 to £1,600, but they hold less water and don’t last as long. A smaller garden soakaway for a single downpipe might cost £500 to £700.
If your soil is difficult (clay, rock, or a high water table), expect to pay more. Excavation in clay is slower, and you may need a larger system to compensate for poor drainage rates. Getting a proper site assessment before you commit saves money in the long run, because it tells you exactly what you’re dealing with underground.
Building regulations and compliance
Soakaways are covered by Building Regulations Part H (drainage and waste disposal). If you’re installing one as part of a building project, extension, or new driveway, you’ll usually need Building Control approval. That means a design with supporting calculations, a percolation test, and confirmation that the soakaway sits at least five metres from any building and isn’t in an area with a high water table.
French drains don’t always need formal approval, but if they discharge into a watercourse or public sewer, you may need consent from your local water authority. Scottish Water handles this in Scotland, while water companies like Thames Water, United Utilities, and others manage it in England and Wales.
Both systems also fall under SuDS (Sustainable Drainage Systems) guidance, which encourages managing rainwater on site rather than sending it into public sewers. New developments are increasingly required to include SuDS as part of planning conditions, and both French drains and soakaways count towards compliance.
What about clay soil?
Clay soil is the biggest challenge for both systems, but it hits soakaways harder. Because soakaways rely on water percolating into the surrounding ground, heavy clay that barely drains can turn your soakaway into an underground pond. A percolation test is non-negotiable before installing a soakaway in clay, and if the results are poor, you may need to look at alternatives like connecting to a new drainage run or a watercourse instead.
French drains cope better with clay because they’re moving water along a pipe rather than relying on the soil to absorb it. As long as there’s a gradient and a discharge point, a French drain will work in clay ground. The gravel backfill around the pipe still needs to be free-draining aggregate, though, not the clay you’ve just dug out.
Signs your property needs better drainage
Not sure whether you even need a French drain or soakaway? Watch for these warning signs:
- Puddles that linger on your lawn for days after rain stops
- Damp patches or green algae on walls near ground level
- Water pooling against your house or in the corners of patios
- A musty smell in your cellar or underfloor area
- Cracks in retaining walls or boundary walls
- Downpipes that discharge onto the ground with nowhere for the water to go
If any of these sound familiar, a professional drainage survey can pinpoint the source of the problem and tell you whether a French drain, soakaway, or a combined system is the right fix. It’s a lot cheaper than guessing and ending up with a system that doesn’t solve the issue.
Frequently asked questions
Do I need planning permission for a French drain or soakaway?
You don’t usually need planning permission for either, but soakaways installed as part of a building project need Building Control approval under Part H. If a French drain discharges into a public sewer or watercourse, you’ll need consent from your water authority. It’s always worth checking with your local council before starting work.
How long do these systems last?
A well-installed French drain with quality geotextile membrane and aggregate can last 20 to 30 years or more. Soakaways using plastic crates have a similar lifespan, while rubble-filled soakaways tend to silt up faster and may need replacing after 10 to 15 years. Regular drain cleaning and maintenance extends the life of both systems.
Can I install a French drain or soakaway myself?
Smaller garden French drains are a manageable DIY project if you’re comfortable with digging and levelling. Soakaways are trickier because the sizing, placement, and compliance requirements mean getting it wrong can cause problems with Building Control or, worse, with your foundations. For anything beyond a straightforward garden drain, professional installation is worth the investment.
How deep does a soakaway need to be?
Most domestic soakaways sit between 1 and 2 metres deep, though this depends on the volume of water they need to handle and the percolation rate of your soil. The base of the soakaway should be above the water table at all times, and it needs to be at least 5 metres from any building. A drainage engineer can calculate the correct size based on your property’s roof area, ground conditions, and local rainfall data.
Getting it right first time
Whether you need a French drain, a soakaway, or a combination of both, the starting point is always the same: understand where the water is coming from and where it needs to go. Guessing leads to wasted money and persistent flooding.
Clark Drainage carries out drainage installations and surveys across the UK, with engineers who can assess your site, test your soil, and recommend the right system for your property. If you’re not sure what’s going on underground, a CCTV survey takes the guesswork out of it completely.
Call us on 0800 085 1219 for a free quote, or visit our contact page to book a survey.
