Why we wrote a new framework for SuDS compliance – tell us what you think

Ask any civil engineer working in England below the major development threshold and they will tell you the same thing: The compliance system for sustainable drainage (SuDS) does not really exist on a minor scale. 

 

Policy F8 in the National Planning Policy Framework (NPPF) requires SuDS on all development that could affect drainage, and the Planning Practice Guidance adds that requirements should be proportionate to the nature and scale of the proposal. But neither document defines what proportionate means below the major development threshold. 

 

That definition is left to local planning authorities, resulting in a patchwork of local policy, officer interpretation and voluntary guidance, which amounts to something close to nothing consistently. 

 

This is not a minor inefficiency at the edges of the system, it is a structural gap at the centre of it.

England decided around 290,000 planning applications in the year to June 2026. Major residential development, defined as ten or more dwellings or the commercial equivalent, accounts for fewer than 10,000 of them. That is approximately three in 100 decisions.

 

This means that the other ninety-seven planning applications – householder works, small commercial projects, extensions, conversions, new hardstandings – fall into a compliance zone where the national framework offers no meaningful interpretation of the proportionality referenced by Policy F8. 

 

The cumulative surface water impact of those decisions, made every year across the country, is essentially invisible to the regulatory system designed to manage it.

 

As for London, we researched the variation in what all 33 boroughs require of development below the major threshold: Thirty-three different answers to the same question. Some boroughs have detailed supplementary planning guidance, others have a single line in a validation checklist, others nothing at all.

 

In the Borough Blueprint, we mapped each borough’s requirements not as a curiosity but as an indictment, a demonstration that in the absence of national standards, local policy fills the gap inconsistently – and the gap itself does real harm.

 

 

On paper, Schedule 3 was a decisive intervention.  But it was never implemented in England. Wales became the first nation in the world with statutory SuDS legislation of this kind when it adopted Schedule 3 in January 2019. England has spent the fifteen years since Royal Assent consulting, deferring, and retreating. 

 

A 2020 review found the planning-led approach that substituted for statutory implementation was not working. In 2022, the National Infrastructure Commission called for commencement by end of 2023. Another government commitment was made and the deadline passed. 

 

As of early 2025, DEFRA has indicated that a final decision on commencing Schedule 3 will be made in due course, the same holding position it has occupied, with minor variations, since 2014. 

 

In June 2025, the government published a refreshed set of national standards for sustainable drainage. It made them non-statutory guidance and signalled that it favours improving the planning-led approach over commencing Schedule 3.  

 

But the standards resolve nothing for smaller sites. The June 2025 guidance is the government choosing to improve the planning-led approach rather than commence Schedule 3, while still offering no standard whatsoever for development below the major threshold.

 

 

Without Schedule 3, England relies on NPPF Policy F8 to carry the requirement. Policy F8 does require SuDS on all development that could affect drainage, and the Planning Practice Guidance establishes that requirements should be proportionate to the nature and scale of the proposal. 

 

On paper, this is a sound principle. In practice, it is instruction without definition. Neither Policy F8 nor the PPG specifies what proportionate compliance looks like for anything less than major development. The major/minor binary is what you get when a statutory framework is promised but not delivered and planning policy is asked to do work it was never designed to do.

 

The consequence of this delay is a gap in compliance. That gap is what we created a framework to address. We felt so strongly about the need for it that we wrote it ourselves. We’re running a free event to introduce it on 7 December, so please attend to find out more and have your say.

 

The Wales model is proof that mandatory requirements work. The 2023 post-implementation review found that all partners and stakeholders recognised the benefits and positive outcomes of Schedule 3 in Wales. There were challenges with implementation, but these were second-order, for example, the consistency of interpretation, approval body capacity and maintenance funding structures. The principle was vindicated. 

 

The Wales model has a deeper limitation than the gap below 100m², however. It did not redesign the compliance architecture; it simply redrew the line. A 110m² infill dwelling in Wales enters the same full statutory approval process as a city centre regeneration scheme. The requirement is not calibrated to the scale of the intervention. It is a blunt instrument applied at a lower trigger point.

 

The framework proposed here does something structurally different. It does not ask where the line should be. It asks whether a single line is the right architecture at all. The answer is no. The Wales model is proof that mandatory requirements work. It is not a model for how those requirements should be calibrated. What is needed is a system where the nature of what is required changes at each scale of development, not just the threshold at which something is required.

 

What we need is a framework, specific, tiered, technically grounded, that describes what proportionate SUDS compliance should look like at every scale of development, from a householder paving their driveway to a major mixed-use scheme reshaping an urban neighbourhood.

 

We felt so passionately about the need for this framework at EGY Design, that we wrote it. It’s open access and free to use – and we’re also hosting a free online event on 7 December, please register and come along to find out more and tell us what you think.

 

The framework has four tiers, defined by the nature and scale of the development: Lite, Level 1, Level 2 and Level 3. Each tier has a fixed compliance mode: the type of requirement changes at each step, not just the amount. Each tier specifies what must be achieved, who delivers it, and how compliance is demonstrated.

 

This is not a novel concept in the built environment. The principle of calibrated compliance exists across planning, building safety, environmental permitting, and biodiversity net gain. What is novel is applying it to SUDS at the small end of the development spectrum, the scale where it has always been needed most and has always been absent.

 

One distinction is worth making explicitly: The tiers here are minimum compliance standards, not aspirational ratings. There is no score to negotiate, no credits to trade. You either meet the standard for your tier or you do not. The graduation is in what the standard requires, not in how loosely it is applied.

 

The argument for a tiered compliance framework rests on a single principle: Compliance should be proportionate to impact.

 

 

The current system violates this principle in both directions. It applies one standard to all development above the major threshold, regardless of whether that development is ten units or five hundred, and no standard at all to everything below it. The threshold is an administrative convenience, not a drainage standard. A 9-unit scheme and a 10-unit scheme are hydraulically indistinguishable. The line between them exists because someone had to draw a line somewhere, not because the line makes engineering sense.

 

A tiered framework would replace administrative convenience with proportionality. It acknowledges that a homeowner adding a rear extension has a drainage obligation, because impermeable surfaces in dense urban areas have cumulative consequences that are well documented and, in aggregate, significant. But that obligation should not be the same as that of a developer building a 200-unit scheme. What is needed is a framework that scales the requirement to the intervention and ensures the nature of what is required changes at each tier, not just the quantity of it.

 

The framework is not a policy proposal waiting for government approval. It can be adopted by any local planning authority using existing powers, embedded in validation checklists, drainage conditions, and supplementary planning guidance. Several London boroughs are already part of the way there. The framework gives them, and every other authority, a coherent, technically grounded reference point.

 

 

What we want is four specific things. First, that progressive LPAs adopt the framework as local policy, using existing powers to embed Lite and Level 1 requirements in householder and minor development validation.

 

Second, that the Ministry of Housing, Communities and Local Government (MHCLG) consider the Lite tier as a Building Regulations amendment – a simple, enforceable, product-level requirement that does not depend on planning at all. The precedent exists in Part H. The requirement is simple enough to work.

 

Third, that the profession (CIWEM, ICE, CIRIA…) develops a standardised calculation tool that makes proportionate compliance possible without bespoke engineering commissions for every minor application. The tool needs to exist before the requirement can scale.

 

Fourth, that DEFRA and MHCLG use this framework as an input to what England’s Schedule 3 implementation should specify. The Wales model proves that mandatory requirements work. This framework proposes how to calibrate them proportionately for a system that runs from a garden extension to a major urban development.

 

The framework is available to download and we’re inviting feedback. We want it challenged, improved, and adopted. If you work in planning, engineering, architecture or policy and want to discuss what this means for your practice or your authority, please reach out, we want to hear from you.

 

Paul Davis is co-founder of EGY Design

 

Find out more Download the Beyond major and minor framework, free of charge, at egydesign.co.uk/publications/

 

Register now for a free Festival of Place Bytesize event: Beyond major and minor: A new proportionate framework for SuDS compliance run in association with EGY Design on 7 December, bringing together practitioners, local authorities and policymakers to discuss what proportionate SuDS compliance should look like in practice.