JD Drainage Solutions
Soakaway Installation
That Eliminates Standing Water
And Protects Your Property
Standing water damages foundations, erodes landscaping, and creates hazards. We design and install soakaway systems that manage surface water reliably — sized for your property, built to last, and compliant with Building Regulations.
25+
Years of Experience
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Building Regs Compliant
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Percolation Testing
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What Is a Soakaway and How Does It Work?
A soakaway is a subsurface drainage structure designed to collect surface water runoff — from roofs, driveways, patios, and hard surfaces — and allow it to percolate gradually into the surrounding ground. Instead of overloading the public sewer system, a soakaway disperses rainwater naturally through the soil.
Modern soakaways use modular crate systems (geocellular units) wrapped in geotextile membrane, installed in an excavated pit and backfilled. These systems provide high void ratios (typically 95%) meaning they store large volumes of water in a compact footprint. Older soakaway designs used rubble-filled pits, which have lower storage capacity and degrade over time.
Soakaways are required under Building Regulations Part H for new-build properties and extensions where connection to the public surface water sewer is not available. Many local planning authorities also require soakaways as part of sustainable drainage (SuDS) strategies to reduce flood risk.
We design, install, and repair soakaways for domestic and commercial properties. Every installation begins with a percolation test to confirm the ground can absorb water at a sufficient rate — the most common reason soakaways fail is that they were installed without testing.
What Happens When Surface Water Has Nowhere to Go?
Without effective surface water management, rainwater collects against foundations, saturates soil, and creates hydrostatic pressure against basement walls and footings. Over time, this causes damp, efflorescence, and in severe cases, structural subsidence.
Waterlogged gardens become unusable for months of the year. Patios flood. Driveways develop standing water that freezes in winter, creating slip hazards. Lawns become boggy, killing grass and promoting moss growth.
Failed or undersized soakaways are a common problem in UK properties. Rubble-filled soakaways installed decades ago lose capacity as the voids fill with silt and soil. Soakaways installed without percolation testing may have been placed in clay soil that cannot absorb water at the required rate.
Connecting surface water to the foul sewer — a common illegal shortcut — causes sewer overloading during heavy rain, sewage flooding at downstream properties, and potential prosecution by the water authority. The solution is a properly designed, correctly sized soakaway installed in suitable ground.
How We Install a Soakaway
Site Assessment & Percolation Test
We visit your property, assess the drainage layout, and conduct a percolation test — digging a trial pit and measuring how quickly water drains from it. This determines whether the ground is suitable and what size soakaway you need.
Design & Specification
Based on percolation results, roof area, and surface water volume, we calculate the required soakaway capacity and specify the crate system, membrane, and connecting pipework.
Excavation
We excavate the pit to the required dimensions, maintaining the minimum 5-metre distance from any building as specified in Building Regulations. The base is levelled and lined with geotextile membrane.
Crate Installation & Connection
Modular crates are assembled in the pit, wrapped with geotextile membrane, and connected to the incoming surface water pipework. Inspection chambers are installed to allow future access and maintenance.
Backfill, Testing & Sign-Off
The pit is backfilled and the surface reinstated. We test the system by running water through the entire installation, confirming flow rates and capacity. Building Control sign-off is arranged where required.
Benefits of a Properly Installed Soakaway
Eliminates Standing Water
Surface water drains away within hours of rainfall instead of pooling on driveways, patios, and lawns. Your outdoor spaces remain usable year-round.
Protects Foundations
Controlled water dispersal prevents soil saturation near your property, reducing the risk of subsidence, damp, and structural movement.
Building Regulations Compliant
Every installation meets Part H requirements and is designed to pass Building Control inspection. Essential for extensions, conversions, and new builds.
Reduces Flood Risk
By managing rainwater on-site rather than sending it to the sewer, soakaways reduce the burden on public infrastructure and lower flood risk in your area.
Low Maintenance
Modern crate soakaways require minimal maintenance. An annual inspection of the inlet chamber and occasional clearing of leaf debris keeps the system performing for decades.
Increases Property Value
A properly documented drainage system — with percolation test results and Building Control sign-off — is an asset at resale, avoiding the delays and price reductions caused by drainage uncertainty.
Soakaways: Design, Materials & Regulations
Soakaway sizing is governed by BRE Digest 365, which calculates the required storage volume based on rainfall intensity, contributing area (roof and hard surfaces), and the soil's percolation rate. The percolation test (also called a soakaway test or infiltration test) measures how many seconds it takes for water to drop 1mm in the trial pit — the Vp value. Soils with Vp values between 12 and 100 are suitable for soakaways. Values outside this range indicate the ground drains too quickly (potential contamination risk) or too slowly (soakaway will not function).
Modern soakaway crate systems — brands such as Polypipe Polystorm, Wavin AquaCell, and Marley Mantis — provide 95% void ratios in a compact, structural module. Crates interlock to form the required volume, are wrapped in geotextile membrane to prevent silt ingress, and are strong enough to be installed under driveways and parking areas with appropriate cover depth.
Building Regulations Part H requires soakaways to be positioned at least 5 metres from any building and at least 2.5 metres from any boundary. The invert level of the soakaway must be above the water table to function correctly. In areas with high water tables, alternative drainage strategies may be required.
For properties on clay soil — common across much of Hampshire, Dorset, and Wiltshire — traditional soakaways may not be viable. In these cases, we design alternative solutions including lined attenuation tanks with controlled discharge to watercourses, French drains, and linear soakaway trenches that maximise the contact area with permeable soil layers.
Surface water from driveways and parking areas may require oil interceptors or silt traps before entering the soakaway, particularly on commercial properties or sites where vehicle washing occurs. We design these pre-treatment stages into the system where required.
Failed existing soakaways can often be rehabilitated rather than replaced. If the original pit is in suitable ground and the correct distance from buildings, we can retrofit modern crate systems within the existing excavation, dramatically increasing capacity without the cost of a completely new installation.
Every soakaway installation we complete includes full documentation: percolation test results, design calculations, installation photographs, and a completion certificate. For Building Control purposes, this documentation demonstrates compliance and facilitates sign-off.
Frequently Asked Questions
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