What is a rainwater SOAKAWAY :

A soakaway is simply a hole dug into the ground, filled with plastic crates/ rubble or stone, this creates a void where rainwater can be stored which allows surface water to filter gradually back into the ground close to where it falls.

Why is a Soakaway Useful?

To provide an efficient way for the rain/storm water to be dispersed into the ground evenly and quickly and to prevent flooding. It will also help prevent water damage and damp to your house/commercial property.

Soakway Regulations:

  • Check local building regulations or employ a professional company
  • Should be at least 5 metres away from an building
  • At least 2.5 metres away from your house/business boundary
  • Size and volume of a soakaway should be based on drainage calculations.
  • Position your soakaway on soft turf in order for the excess water to drain away
  • Land drainage pipe should be at least 75mm diameter, however 100mm diameter is the recommended size

Soakaway Design & Constuction:

Firstly, you’ll need to dig your trench on your turf in which you can install your drainpipe, then the pit for the soakaway itself. You can use a shovel and do this by hand or hire a mini-digger, but ultimately the hole that hosts your soakaway should be 1m3 at the very least – you may well need to go larger, depending on your requirements. Soakaways need to be at least 5 metres away from the building foundations or 2.5 metres away from your house boundary.

Lay some gravel across the bottom of this freshly dug ground to level out the surface, and you’re ready to fill the soakaway with rubble. These broken stones should surround the drainpipe and finish around 100mm above it.Alternatively, if you prefer to use a more modern alternative, you could install a modular water cells or soakaway crate. These can be purchased from any DIY shop and resemble giant plastic milk crates that can be easily snapped together, and negate the need for any kind of rubble. If you use a soakaway crate, just dig your hole to the appropriate dimensions and feed in your drainpipe, then fill the surrounding area with soil.

Whichever storage technique you use for your soakaway, you’ll need to place a layer of impenetrable material over the top, which could be constructed of anything frompolyethene to concrete. Once this is done and you are happy with your installation,and you are happy you have followed building regulations and replace your soil and turf.

Soakaway FAQ's

Is a Soakway Expensive to Install?
As always, this depends on whether you embark on the project entirely as a DIY venture, or if you will be bringing in the services of a professional – there are many specialist companies all over the country that specialise in these installations. If you do bring in outside help, be sure to consult your local water supplier as you could be eligible for a rebate on future bills.

Can you clear a blocked soakaway?
Yes in some cases but 1st you need to find out what type of soakaway blockage you are dealing with.

How big does a soakaway have to be?
Measure the length of the roof from one end of the eaves to another, then measure the width of the gable end/hip end and divide this number by 2. Now multiply together the two figures

I Have Clay Soil on My Property – Can I Still Use a Soakaway?
Maybe, but it’s very unlikely to be successful – you really need soft soil to garner the benefits of a soakaway. Consult a professional before spending any time or money on such a project to confirm that it’s a viable option.

Drain Doctor Soakaway Specialists :

We have over 20 years of experience in designing & installing new commercial & domestic soakaways. We do everything from the initial survey.

Building Regulations 2010 – Drainage & Waste Disposal.

Septic tanks

1.15 - Septic tanks should only be used in conjunction with a form of secondary treatment (eg, a drainage field, drainage mound or constructed wetland).


1.16 - Septic tanks should be sited at least 7m from any habitable parts of buildings, and preferably downslope.

1.17 - Where they are to be emptied using a tanker, the septic tank should be sited within 30m of a vehicle access provided that the invert level of the septic tank is no more than 3m below the level of the vehicle access. This distance may need to be reduced where the depth to the invert of the tank is more than 3m. There should also be a clear route for the hose such that the tank can be emptied and cleaned without hazard to the building occupants and without the contents being taken through a dwelling or place of work.

Design and construction

1.18 - Septic tanks should have a capacity below the level of the inlet of at least 2,700 ltres (2.7m3) for up to 4 users. The size should be increased by 180 litres for each additional user.

1.19 - Factory-made septic tanks are available in glass reinforced plastics, polyethylene or steel and should meet the requirements of BS EN12566-1. Particular care is necessary in ensuring stability of these tanks.

1.20 - Septic tanks may also be constructed in brickwork or concrete, roofed with heavy concrete slabs. Brickwork should be of engineering bricks and be T LEAST 220MM THICK. The mortar should be a mix of 1;3 cement-sand ratio. In situ concrete should be at least 150mm thick of C/25/P mix

1.21 - Septic tanks should prevent leakage of the contents and ingress of subsoil water and should be ventilated. Ventilation should be kept away from buildings.

1.22 - The inlet and outlet of a septic tank should be designed to prevent disturbance to the surface scum or settled sludge and should incorporate at least two chambers or compartments operating in series. Where the width of the tank does not exceed 1200mm the inlet should be via a dip pipe. To minimise turbulence, provision should be made to limit the flow rate of the incoming foul water. For steeply laid drains up to 150mm the velocity may be limited by laying the last 12m of the incoming drain at a gradient of 1 in 50 or flatter.

1.23 - The inlet and outlet pipes of a septic tank should be provided with access for sampling and inspection.

1.24 - Septic tanks should be provided with access for emptying and cleaning. Access covers should be of durable quality having regard to the corrosive nature of the tank contents. The access should be lockable or otherwise engineered to prevent personnel entry.


1.25 - A notice should be fixed within the building describing the necessary maintenance,

Drainage fields and drainage mounds

1.26 - Paragraphs 1.27 to 1.44 give guidance on design and construction of drainage fields and drainage mounds to provide secondary treatment to the discharge from a septic tank or package treatment plant.


1.27 - A drainage field or mound servicing a wastewater treatmentplant or septic tank should be located:

A. - at least 10m from any watercourse or permeable drain;

B. - at least 50m from the point of abstraction of any groundwater supply and not in any Zone 1 groundwater protection zone;

C. - at least 15m from any building;

D. - sufficiently far from any other drainage fields, drainage mounds or soakaways so that the overall soakage capacity of the ground is not exceeded.

1.28 - The disposal area should be downslope of groundwater sources.

1.29 - No water supply pipes or underground services other than those required by the disposal system itself should be located within the disposal area.

1.30 No access roads, driveways or paved areas should be located within the disposal area.

1.31 - Well drained and well aerated subsoils are usually brown, yellow or reddish in colour. Examples of subsoils with good percolation characteristics are sand. gravel, chalk, sandy loam and clay loam. It is important that the percolation characteristics are suitable in both summer and winter conditions. Poorly drained or saturated sunsoils are often grey or blue in colour. Brown and grey motting usually indicates periodic saturation, Examples of subsoils with poor percolation characteristics are sandy clay. Silly clay and clay.

1.32 - A preliminary assessment should be carried out including consultation with the Environment Agency and local authority to determine the suitability of the site. The natural vegetation on the site should also give an indication of its suitability for a drainage field.

1.33 - A trial hole should be dug to determine the position of the standing groundwater table. The trial hole should be a minimum of 1m2, In area and 2m deep, or a minimum of 1.5m below the invert of the proposed drainage field pipework. The groundwater table should not rise to within 1m of the invert level of the proposed effluent distribution pipes. If the test is carried out in summer, the likely winter groundwater levels should be considered. A percolation test should be carried out to assess the further suitability of the proposed area.

1.34 Percolation test method – A hole 300mm square should be excavated to a depth 300mm below the proposed invert level of the effluent distribution pipe. Where deep drains are necessary the hole should conform to this shape at the bottom, but may be enlarged above the 300mm level to enable safe excavation to be carried out. Where deep excavation s are necessary a modified test procedure may be adopted using a 300mm earth auger. Bore the test hole vertically to the appropriate depth taking care to remove all loose debris.

1.35 - Fill the 300mm square section of the hole to a depth of at least 300mm with water and allow it to seep away overnight.

1.36 - Next day, refill the test sectionwith water to a depth of at least 300mm and observe the time, In seconds, for the water to seep away from 75% full to 25% full level (i.e. a depth of 150mm). Divide this time by 150. The answer gives the average time in seconds (Vp) required for the water to drop 1mm.

1.37 - The test should be carried out at least three times with at least two trial holes. The average figure from the tests should be taken. The test should not be carried out during abnormal weather conditions such as heavy rain, severe frost or drought.

1.38 - Drainage field disposal should only be use when percolation tests indicate average values of Vp of between 12 and 100 and the preliminary site assessment report and trial hole tests have been favourable. This minimum value ensures that untreated effluent cannot percolate too rapidly into groundwater. Where V, is outside these limits effective treatment is unlikely to take place in a drainage field. However, provided that an alternative form of secondary treatment is provided to treat the effluent from the septic tanks, it may still be possible to discharge the treated effluent to a soakaway.

Design & construction

1.39 - Drainage fields or mounds (see diagrams 1 and 2) should be designed and constructed to ensure aerobic contact between the liquid effluent and the subsoil.

1.40 - Drainage fields should be constructed using perforated pipe, laid in trenches of a uniform gradient which should be not steeper than 1:200.

1.41 - Pipes should be laid on a 300mm layer of clean shingle or broken stone graded between 20mm and 50mm.

1.42 - Trenches should be filled to a level 50mm above the pipe and covered with a layer of geotextile to prevent the entry of silt. The remainder of the trench can be filled with soil; the distribution pipes should be laid at a minimum depth of 500mm below the surface.

Drainage trenches should be 300mm to 900mm wide, with areas of undisturbed ground 2m wide being maintained between parallel trenches (see Diagram 1).

1.43 - An inspection chamber should be installed between the septic tank and the drainage field.

1.44 - Drainage fields should be set out as a continuous loop fed from the inspection chamber (see Diagram 1). To calculate the floor area of the drainage field (A, in M2), the following formula should be used.

A, = p x Vp x 0.25

Where p is the number of persons served by the tank, Vp is the percolation value (secs/mm) obtained as described in paragraphs 1.34-1.38.