Soakaway Design Package – Drainage Area 100m2 or Less



By purchasing this service you will receive:

  • BRE-365/Building Regulations compliant soakaway design
  • Detailed plan of your new soakaway, superimposed on your drawing(s), or sketch if required in PDF format (paper copy on request*)
  • Detailed soakaway calculations for Building Control/Planning Authority in PDF format (paper copy on request*)
  • Construction detail for your new soakaway in PDF format (paper copy on request*)

Important! This particular soakaway design service is for drainage areas measuring 100m2 or less. Simply multiply the length of the new building by the width to calculate your drainage area. Please don’t worry about roof pitch when calculating your drainage area, a plan view measurement will be fine. For complex shapes, driveways or other areas that may prove difficult to calculate on site or on a drawing, simply email your proposals in PDF or AutoCAD (preferred) format to and we will measure it for you.

This service is perfect to ensure you construct and install a soakaway that is designed correctly and meets modern building regulations requirements. In order to obtain your soakaway design please follow the steps below:


Measure your drainage area. This is achieved by measuring the length and width of the building and multiplying the two figures together. For example, if you are building a conservatory that measures 8m wide x 4m long, simply multiply these figures to give a drainage area of 32m2. Remember, you don’t need to worry about roof pitch etc. Please ensure you include all impermeable surfaces (any areas that wont self drain eg, grass, shrub beds etc) that will drain to the soakaway as these will need to be included in the calculations. We can measure your drainage area for you if you have complex shapes such as long driveways etc or required additional assistance. Simply email your plan to and we will do the rest.


Purchase the design package that reflects your drainage area. This package is for drainage areas that measure 100m2 or less. You can either purchase directly through our website, pay by BACS transfer or we can send you a Paypal invoice.

Other design packages for different drainage areas can be purchased through our website.


Once you have completed your purchase you will need to email info@soakawaysolutions with the following information:

  • Provide a copy of your site/architects layout in PDF or AutoCAD (preferred) format. If you only have sketches please scan these and email them ensuring they contain accurate dimensions.
  • Confirm the design criteria for your soakaway design. We recommend you contact your building control officer or planning officer for this information as all local authorities work to different criteria. The default criteria is to design to BRE-365 requirements, however, with modern day flooding issues some authorities ask for us to design soakaways to accommodate larger storm duration’s such as a 100 year storm event + allowance for climate change. If you are installing a soakaway as a independent project and building control are not involved then BRE-365 criteria will be fine.
  • Soakaways fundamentally rely on the porosity of the soil to function correctly. For example, clay soils are far more likely to be less permeable than sands and gravels. As such, a soakway installed in clay will need to be larger as the water will take far longer to drain into the ground. In order to design the soakaway we will need to know the porosity of the soil before we can calculate the soakaway size required. There are two ways we can do this, the first is by undertaking a BRE-365 soakaway test on site to enable us to accurately calculate the soil infiltration rate, the second option is to base the design on known typical infiltration rates for the soil type stipulated within published geology maps at your property. We recommend again that you discuss this with your building control officer. Should on-site soil testing be required, we can send you instructions on how to conduct the test yourself, however, should building control confirm they are satisfied with us using geology maps then we can obtain this information directly, just provide your postcode. We always recommend on site soil testing as this is by far the most accurate way to calculate a soakaway.
  • Provide us with any other information that may help us design your soakaway. Information such a site investigation report, planning permission document or any knowledge of high water table or areas of contamination are always useful.

We design soakaways on the basis that they will be installed using modern day soakaway crates providing a 95% void ratio. Should you wish to install a rubble filled soakaway then please let us know. Please be aware that rubble soakaways are now considered inefficient as they only offer a 30% void ratio and some authorities no longer permit their usage.


We design your soakaway then email or post* your drawings and calculations to you.

We aim to design soakaways within 7 days of receipt of information required in step 3. Larger or more complex jobs may take longer, we will advise of this at the earliest opportunity.

*Additional charges apply for paper copies