By Catherine Thorpe and Ollie Manston
One year ago, the UK Government launched new National Standards for Sustainable Drainage Systems (SuDS). In our original analysis, our team at Pegasus Group expressed cautious optimism that the guidance would ‘hopefully allow for easier development in tight urban environments where SuDS can be difficult to implement.’
The question now, of course, is whether that optimism has survived a year of live projects and conversations with Lead Local Flood Authorities (LLFA). In theory, the guidance remains sound, and we maintain that the guidance has helped elevate the importance of sustainable drainage, on top of encouraging better development outcomes.
In practice, however, interpretations of the guidance by local authorities have been rather variable, due to the resource pressures that LLFAs face and the lack of established precedence.
At Pegasus Group, we have spent the last year helping developers ensure their projects remain viable but still compliant with the principles of the national standards. Here are the biggest observations we have made.
With councils facing resource challenges, interpretations of national SuDS guidance have been inconsistent
A key ambition of the SuDS guidance from a policy perspective in England was to make the assessment of drainage and flood risk more consistent. In reality, the guidance is being interpreted inconsistently.
The projects we have supported in the last year have shown this inconsistency quite clearly. Different LLFAs have requested anywhere between a 1:1 and 1:10 ratio of SuDS to impermeable area. The former would not be commercially viable for residential developments, and the latter would be unlikely to technically comply with the Standard 2 requirement (interception storage) where infiltration is unviable.
In our experience, the LLFAs are limited by their lack of resource and availability of in-house technical engineers. For a while now, local authorities have struggled to recruit and retain specialist drainage expertise, which means they are often short-staffed and look to outsource technical review to environmental consultancies. That pressure has only grown since the new standards landed, which are asking already-stretched teams to correctly understand and apply a far more technically demanding framework.
Meanwhile, developers are struggling to balance commercial viability against the technical demands of national standards. Increasingly over the past year, our position as sustainable drainage consultants has become more focused on negotiation. This has meant working hard in consultation with the LLFAs to agree on deliverable and environmentally sustainable drainage solutions, which does not preclude development on viability terms.
The natural consequence is that developers must be more proactive in anticipating the knock-on effects of these resource shortages. Whether it’s longer review times or objections that do not correctly apply national guidance in a technically deliverable or commercially viable way, early-stage consultations are very important.
SuDS standards are impacting the viability and design of residential schemes – forcing developers to change their approach from day one
Another reason developers must be proactive is because the national SuDS standards are affecting land use in a very real and measurable way – especially for residential projects.
Whereas drainage requirements on a typical housing project could have once sat at about a 10:1 ratio of developable land to drainage infrastructure, many schemes now sit closer to 5:1. That’s no trivial shift, and on some residential sites, it has significantly cut the realistic number of homes that can be delivered.
This puts more onus on developers to rethink how they approach schemes from day one. Trying to retrofit drainage around a design layout that’s already finished won’t work. Developers must consider public open space and SuDS at the start of the design process; ideally, around what the site can actually accommodate, not the other way around.
A few of the more specific trends we have seen include:
- Infiltration tests are required earlier in the project timeline, with a larger number of tests recommended.
- Rainwater reuse, once often discounted for residential developments, is becoming a non-negotiable for the LLFAs.
- Features like permanent water in attenuation basins, traditionally valued for biodiversity net gain (BNG), can now sit awkwardly against the interception storage requirements in the new guidance.
There are many other knock-on effects of SuDS to consider, but the point is that you need to consider all the details from a multidisciplinary lens. Bringing together the likes of drainage engineers, ecologists, designers, and landscape architects will help resolve competing design objectives and unlock more efficient solutions. The same cannot be said if those experts are working in sequence or in isolation.
What developers must do: engage early with local authorities
Given the above challenges, the single biggest lesson to understand is this: timing is now more important than ever. The earlier you consider drainage (ideally before layout and massing are locked in), the smoother the planning process will be.
Early infiltration testing, early engagement with LLFAs, and early collaboration between drainage, ecology, design, landscape, and planning will reduce the risk of costly redesigns later on. Even though the SuDS standards are currently non-statutory, it’s incredibly important to apply them correctly on a project, not just because they support climate resilience, but also because of the commercial opportunity they provide.
Done well, the new standards push development toward multifunctional green infrastructure: ponds, swales, rain gardens, and shared open space that do more than manage water. These are the features that make a development desirable for people to live in. As community expectations continue to shift away from purely functional and high-density layouts, this will give developers a significant commercial advantage. To put it another way, SuDS doesn’t have to be ‘just another compliance cost to absorb.’
How Pegasus Group can support your project with implementing SuDS
The new standards for SuDS are a good step forward for the built environment. Treating drainage as multifunctional green infrastructure instead of merely a flood control measure is still the right idea.
But guidance is only ever as good as its implementation, and given the challenges councils are confronting, developers will need to meet them halfway in filling the expertise gap. That gap is exactly where experienced and multidisciplinary advice comes in handy – not just in interpreting the guidance the right way, but in helping authorities and developers reach the same understanding. It also helps facilitate developments that are both environmentally sustainable and commercially viable.
As the application of the national standards is still evolving, we have the opportunity through consultation with the LLFAs to create the delivery case studies of the future. This will ensure those case studies include exemplar sites which achieve a successful balance between sustainability and commercial viability.
If you’re interested in discussing how the new SuDS standards are affecting your development, please get in touch with either Catherine Thorpe or Ollie Manston.
