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Soakaway Repairs & Installation in Dorchester

For surface water that has nowhere to go — repairs to failed soakaways and new installations.

Call 0330 133 1625 Request a quote

What is a soakaway and how does it work?

A soakaway is an underground chamber that takes rainwater from roofs and paving and lets it seep slowly into the surrounding ground, instead of sending it to a sewer.

Water arrives through a pipe, fills the open space inside the soakaway, and drains out through its sides and base at whatever rate the soil allows. The soakaway is a buffer: it holds a downpour that arrives in minutes while the ground absorbs it over hours.

Older soakaways are usually a pit filled with rubble or hardcore, with water held in the gaps between the stones. Modern ones use plastic crates, which hold far more water for their size, wrapped in a fabric membrane that lets water out and keeps soil from washing in.

How do I know if my soakaway has failed?

The clearest sign is standing water that forms faster and lingers longer with each spell of rain, until the ground over or near the soakaway barely drains at all.

Other signs:

  • Gullies and downpipe shoes overflowing in heavy rain
  • Downpipes backing up, or gutters overflowing with no blockage in them
  • A patch of lawn that stays soft or sodden over the soakaway
  • Damp at the base of a wall near a downpipe
  • A soakaway that copes in summer but fails every winter

Because it happens slowly, people tend to describe it as the garden getting boggier each year rather than as something broken. If water is now pooling against the house walls or reaching airbricks, treat it as urgent: we take calls across Dorchester 24/7 on 0330 133 1625.

What causes a soakaway to fail?

Most soakaways fail because silt, leaves and fine soil wash in and fill the spaces that should hold water, until it has nowhere left to go.

Other causes are common too:

  • No silt trap, or one that has never been emptied
  • A missing or torn membrane, letting surrounding soil migrate in
  • Roots growing into the pit and its inlet pipe
  • Undersizing, especially where an extension or new paving now drains to an old soakaway
  • Ground that drains poorly, or a water table that rises in wet months
  • Compaction from vehicles or building work over the top
  • A foul pipe wrongly connected to it, which clogs the soil with grease and solids

Rubble soakaways are the most likely to silt up over time, because they were rarely built with any protection.

Is it the soakaway or the pipe leading to it?

Waterlogging can come just as easily from a blocked or broken pipe on the way to the soakaway as from the soakaway itself, so the pipe is checked first.

A simple test helps. If a gully or downpipe backs up while the ground over the soakaway stays dry, the water is probably not reaching it, which points to the pipe. If the soakaway's inspection point is full to the top and slow to fall after rain, the soakaway is the problem. A camera along the inlet pipe settles it: we look for silt, roots, crushed sections or a run with no fall. Replacing a soakaway that was never the fault is an expensive way to find out, so we establish the cause first.

Can a blocked soakaway be repaired, or does it need replacing?

A soakaway blocked by silt in its inlet or silt trap can often be cleared; one whose fill and surrounding soil are choked throughout needs replacing.

Repair options include jetting the inlet pipe, emptying and cleaning a silt trap, cutting out roots and, on crate soakaways with access, jetting silt out of the crates. These restore capacity where the blockage is near the inlet and the ground around the soakaway still drains.

A rubble pit full of compacted silt cannot really be cleaned, since there is no way to wash the gaps out, and the soil face around it is often clogged too. At that point a new soakaway, often in a fresh position with a silt trap ahead of it, is the lasting fix. We tell you which applies before pricing either.

What is a percolation test?

A percolation test, or soakage test, measures how quickly water drains into the ground on your site, and it is the starting point for sizing any new soakaway.

The usual method follows BRE Digest 365. A trial pit is dug to roughly the depth the soakaway would sit, filled with water, and timed as the level falls between set points. It is filled and timed three times in quick succession, because the ground drains more slowly once it is wet, and the slowest result is used for design. The figure tells you whether a soakaway can work at all, and if so how big it must be. Without it, sizing is a guess, and undersized soakaways are one of the commonest failures.

How we install a new soakaway, step by step

We test the ground, size the soakaway to the area it drains, site it safely away from buildings, then build it with a silt trap and access for future maintenance.

  • We agree the scope and a fixed price before starting.
  • We carry out a soakage test where the soakaway would go.
  • We measure the roof and paved area that will drain to it, and size it from that and the test result.
  • We excavate, then install crates wrapped in membrane, or a rubble fill where that suits the site.
  • We lay the inlet pipe with a proper fall and fit a silt trap ahead of the soakaway.
  • We backfill, reinstate the surface as agreed and record the position.

You get a note of where the soakaway is and how big, so nobody has to guess in future.

Where can a soakaway go, and how far from the house?

Building Regulations guidance in Approved Document H says a soakaway should be at least 5 metres from a building, so the water it releases does not soften the ground under foundations.

It also needs to sit where the ground drains, which the soakage test confirms. It should not be placed uphill of the house where water could track back towards it, nor so close to other soakaways or drainage fields that they compete for the same ground. Avoid spots where trees will root into it or where vehicles will compact it. Too close to the building is one of the two failures we see most at installation, along with undersizing, and both are avoidable with planning.

Will a soakaway work in clay soil?

Often not well. Clay drains very slowly, so a soakaway in clay either has to be very large or will fill faster than it empties after heavy rain.

That is exactly what the soakage test is for: it shows whether the ground on your site can take the water, rather than relying on what the soil looks like. Where results are poor, the alternatives are attenuation, which stores the water in a tank and releases it slowly to a watercourse or sewer, or reducing how much water reaches the system through permeable paving, rain gardens or water butts. Connecting to a surface water sewer is the last option and needs the sewerage company's consent.

Soakaway rules: Building Regulations, planning and what can go in

A soakaway must take rainwater only, never foul water, and new rainwater drainage that forms part of building work has to meet Building Regulations Approved Document H.

Approved Document H sets an order of preference for rainwater: an adequate soakaway or other infiltration first, then a watercourse, and a sewer only where neither is reasonably practicable. So building control will usually expect a soakaway on a new extension if the ground allows one, backed by a soakage test. Repairing or replacing an existing soakaway on its own rarely needs planning permission. Paving more than five square metres of a front garden with a hard surface that drains onto the road does, unless the water goes to a permeable area or soakaway instead.

How much does a soakaway cost?

The cost of soakaway work depends on whether it needs clearing, rebuilding or installing new, how large it must be, and how much digging and reinstatement is involved. As a guide, clearing a blocked soakaway by jetting typically costs £150 to £300, repairing damaged pipework £300 to £600, and replacing a standard house soakaway completely £700 to £1,500. We agree a fixed price before work starts.

What drives the price:

  • Repair or new installation, and whether a soakage test is needed first
  • The roof and paved area draining to it, which sets the size
  • Ground conditions and the depth of excavation
  • Access for a digger and for taking spoil away
  • The surface to be lifted and reinstated, such as lawn, gravel or block paving
  • Whether the inlet pipe needs jetting, repair or a new silt trap

If the excavation turns up something unexpected, we pause, show you, and nothing extra is done until you have agreed it.

Who is responsible for a soakaway?

A soakaway and the pipes leading only to it are the responsibility of whoever owns the property it serves.

The 2011 transfer of shared sewers to the water companies covered pipes that connect to the public sewer. Soakaways do not, so a soakaway shared between neighbouring homes generally stayed private, and the owners share its upkeep. On some newer developments a communal soakaway belongs to a management company, which your deeds will say. Gullies in the road are the highway authority's, which for Dorchester is Dorset Council. In rented homes, a failed soakaway is normally the landlord's to put right.

Looking after a soakaway

A soakaway lasts longest when silt and leaves are stopped before they reach it, so most of the maintenance happens upstream at the gutters, gullies and silt trap.

Safe things you can do:

  • Clear gutters and gully grids, especially after leaf fall.
  • Lift the silt trap cover once a year and scoop out what has settled.
  • Keep cars and skips off the ground above the soakaway.
  • Wash patios and cars where the dirty water will not run into a gully that feeds it.
  • Do not connect a new downpipe or paved area to it without checking it has the capacity.

Do not dig down into an old soakaway to look. Rubble pits can collapse, and crates can be damaged by a spade.

Covering Dorchester & the local area

We provide soakaways throughout Charminster, Martinstown, Crossways, Puddletown, Broadmayne, Poundbury and the surrounding area. Call 0330 133 1625 for a free, no-obligation quote.

How it works

Simple, transparent process

  1. 1

    Tell us what’s happening

    Call and describe what you’re seeing — a slow sink, a gurgle, a smell or standing water. It usually tells us a lot before we arrive.

  2. 2

    We find the cause

    We clear enough to get flow back, then work out why it blocked — because a drain that blocks twice has a reason.

  3. 3

    A price before the work

    If it needs more than a clear — a repair, a lining, a survey — you get the price and the reason before we start it.

  4. 4

    You see the evidence

    Where we survey, you get the footage. Where we repair, you see the before and after.

Don't let it get worse

Get expert help right now

Tell us what the drain is doing and we will explain what is likely causing it and what the work involves.

Call 24/70330 133 1625

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Emergency Unblocking

A drain that has stopped completely, water backing up or sewage escaping — the jobs that cannot wait until Monday.

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Blocked Sinks

Kitchen sinks, basins, baths and showers draining slowly or not at all.

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Drain Cleaning

Clearing build-up before it becomes a blockage — for properties that keep having the same problem.

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Soakaways: common questions

How long does a soakaway last?
There is no fixed lifespan; it depends on how much silt reaches it. A soakaway with a silt trap that is emptied, a membrane round it and clean roof water going in can work for many years. An old rubble pit taking silty water from paving with no protection can be choked well before that. Signs of slowing drainage after rain are the best indication that it is nearing the end.
How long does soakaway repair or replacement take?
Clearing an inlet pipe or emptying a silt trap is normally a single visit, and rarely a long one. Installing a new soakaway typically takes a day or more, depending on its size, ground conditions, access for a digger and the surface that has to be reinstated. A soakage test may need its own visit beforehand. The quote tells you roughly how many days to allow.
Why does my soakaway stop working after heavy rain?
Either it is too small for the volume of water reaching it, or it is partly silted and has lost capacity. In wet months the water table can also rise around the soakaway, leaving little dry ground to drain into, which is why some cope all summer and fail each winter. If it drains eventually, it is still working but undersized or clogging; if it barely drains at all, it has probably failed.
Can tree roots damage a soakaway?
Yes. Roots are drawn to the moisture and can grow through the gaps in a rubble pit, into crates through a torn membrane, and into the inlet pipe through its joints. They block the water's path and can break crates or pipework. Planting trees and large shrubs well away from a soakaway avoids the problem, and root growth in the inlet pipe can be cut back during a repair.
Will my insurance cover soakaway repairs?
Usually not for gradual silting, which most buildings policies treat as wear and tear or lack of maintenance. Some policies cover sudden damage, such as a collapse or a pipe broken by an accident, and some cover the damage a failed soakaway causes to the building. It depends entirely on your policy wording, so ask your insurer before work starts. A record of what we find will help either way.
Is a soakaway the same as a septic tank?
No. A soakaway takes clean rainwater only. A septic tank treats sewage from a property not on the mains, and the liquid it releases goes to a drainage field built for that purpose, sometimes loosely called a soakaway. They are designed, sized and regulated differently, and sewage must never go into a rainwater soakaway, where it clogs the ground and can pollute groundwater.
Can I get money off my water bill if my rainwater goes to a soakaway?
Possibly. Sewerage bills often include a charge for surface water drainage, and water companies can reduce it where none of a property's roof or paved water reaches the public sewer. If all your rainwater goes to a soakaway, contact Wessex Water and ask whether your bill already reflects that. They may ask for evidence of where your downpipes discharge.
How do I find my soakaway?
Follow the downpipes. Where a downpipe goes into the ground rather than into a gully that joins the foul drain, its pipe usually heads away from the house towards the soakaway, often under a lawn and at least a few metres out. A patch of grass that stays greener or softer can give it away. If the position is still unclear, a camera can be pushed along the pipe and traced from above.
How deep should a soakaway be?
There is no single right depth. It depends on where the inlet pipe arrives, the depth at which the ground drains well, and how high the water table rises in wet weather, since a soakaway sitting in groundwater cannot empty. The soakage test is dug to roughly the proposed depth for that reason, and the design follows the result rather than a standard figure.
Do I need a silt trap before my soakaway?
It is strongly worth having one. A silt trap is a small chamber in the inlet pipe where grit, leaves and sediment settle out before the water reaches the soakaway. It is far easier to scoop silt out of a trap once a year than to dig up and replace a choked soakaway. If yours has none and drains paving or a gravel drive, adding one is a sensible upgrade.
Can a new driveway drain into my existing soakaway?
Only if the soakaway has spare capacity, which most older ones do not. A drive adds a large hard area and brings silt with it. Permeable paving, which lets rain soak through the surface, often avoids the question entirely. Otherwise the drive may need its own soakaway sized from a soakage test, with a silt trap ahead of it to protect it.