Anyone involved in the design, installation or adoption of below-ground SuDS attenuation assets should be doing their due diligence to ensure they are fit for purpose, says Stuart Crisp of ADS.
Below ground attenuation devices for sustainable drainage systems (SuDS), such as crates, are often considered a commodity. The tendency can be to fit the lowest cost option, given the volume of water required by the engineer’s design.
This may function very well on day one. But how can the ultimate asset owner be sure it will function as intended 10, 20 or more years down the line?
This is the question that any SuDS adopting body will be asking, when Schedule 3 of the Flood and Water Management Act 2010 comes into force in England, making SuDS for new developments mandatory. SABs must assess what maintenance and repair costs might be, in order to agree the commuted sum that a developer pays when handing over the asset
An important part of the due diligence required for below ground SuDS attenuation devices is to check that the products selected meet all the necessary standards, certifications and approvals. To do that properly, it is important to deep dive into the detail of how manufacturers claim that their products comply.
Standards and certifications
The starting point for any construction product to be used in the UK is that it must, by law, have a CE mark or a UKCA mark – although the date from which the UKCA mark will be required has recently been pushed back from June 2025 for at least two years.
Next, products must conform to the relevant standards in terms of both functional performance – which is governed mainly by the evaluation, management and testing of the product’s material properties, manufacturing processes and dimensional tolerances – and the structural design process. These two distinct requirements can sometimes be found in two different standards or alternatively in separate parts of the same standard, depending on the product type and material.
British Standards (BS) are the most well known in the UK but in some cases, a harmonised standard, accepted by multiple nations, could apply, which would be designated BS EN or BS ISO in the UK. Note that there cannot be more than one standard covering the same scope in any territory.
For innovative solutions, where a product standard does not exist, manufacturers must take a different approach. Some choose to cherry pick clauses from different standards in an attempt to demonstrate fitness for purpose, but this is not a reliable approach.
The responsible route is to put the product through an evaluation conducted by a recognised certification body such as the British Board of Agrément (BBA), Water Research Centre (WRc) or British Standards Institution (BSI). This process effectively assesses the key elements that a standard would cover, and checks that the product meets the claims of the manufacturer.
Given the rigour of the testing and checking involved, such approvals understandably take some time to process. ADS was delighted to formally receive its BBA certification for its StormTech range of arch-shaped below ground SuDS attenuation devices in November this year.
Approvals
Across the UK, there are a range of different asset owners that approve SuDS. In England, water companies require developers to follow OFWAT’s Design and Construction Guidance (DCG) for sewers. In addition, the Lead Local Flood Authority (LLFA) must also evaluate and approve drainage designs.
In Scotland, Scottish Water is the adopting body, and SuDS must meet the requirements of Sewers for Scotland 4th edition. The Scottish Environment Protection Agency (SEPA) must also be satisfied that the treatment train is adequate to protect water quality.
In Wales, Schedule 3 of the Flood and Water Management Act was adopted in 2019. The requirement of SABs is based on the Welsh Government’s Statutory Standards for Sustainable Drainage Systems (SuDS) and the CIRIA SuDS Manual, C753.
In a small number of cases, independent adoption bodies such as Icosa Water and Independent Water Networks (IWNL) may take on responsibility for SuDS maintenance. Their requirements are likely to be a version of the DCG.
For devices installed to serve a highway, there is a separate need to demonstrate compliance. For the strategic road network, National Highways’ Design Manual for Roads and Bridges (DMRB) is the most significant document, with local highways authorities often following suit. Products not recognised within National Highways’ standards can be used through the Departure from Standards process.
Of course, the compliance requirements touched on in this article are just one part of the due diligence process for SuDS. Below ground attenuation devices can be rendered unfit for purpose due to other parts of the SuDS system such as inadequate treatment capability, or poor maintenance regimes. Systems such as StormTech, where water treatment comes as an integral part of the device, can provide a straightforward way to alleviate that risk.
