SuDS guidance

Sustainable Drainage Systems (SuDS) offer a nature-based approach to solving drainage issues. They mitigate the effects of rainfall by incorporating grassed and other permeable surfaces, planting trees, creating rain gardens, or constructing attenuation ponds to decrease the likelihood of surface water or river flooding. These systems capture excess rainfall and gradually filter it into the ground, while tree planting provides additional interception, shading, and biodiversity benefits.

Currently, new developments can exacerbate surface and sewer flood risk by covering permeable areas such as grasslands, soil, and existing tree cover, which would normally help absorb heavy rainfall. Protecting tree roots during construction and integrating root-friendly SuDS designs are therefore important for maintaining long-term drainage performance alongside healthier, more resilient landscapes.

Sustainable drainage systems offer numerous advantages, including mitigating flood risk by capturing and storing excess water, reducing storm overflow discharges, enhancing local ecosystems within developments, and facilitating the collection of valuable rainwater. Integrating tree planting into SuDS adds further value by improving interception, supporting biodiversity, and contributing to healthier urban environments. Protecting existing trees and their root zones during construction also helps maintain these natural drainage benefits over the long term.

However, to fully realise these benefits, SuDS must be designed, constructed, adopted, and maintained according to national standards throughout the entire lifespan of a development.

Sustainable drainage systems (SuDS) became mandatory in 2024, following an announcement by the UK government on 30 January 2023. This decision enforces Schedule 3 of the Flood and Water Management Act 2010, requiring SuDS in new developments in England. The move comes after a review by the Department for Environment, Food and Rural Affairs (DEFRA).

In the UK, there isn’t a single SuDS law, but a framework of regulations, planning requirements and national standards that shape how SuDS are applied in construction. The key ones are:

• Flood and Water Management Act 2010
  • Established Lead Local Flood Authorities (LLFAs) and placed responsibility on them to manage surface water flood risk.
• National Planning Policy Framework (NPPF) – England
  • Requires developments in areas at risk of flooding to give priority to SuDS.
  • Planning applications must demonstrate how surface water will be managed sustainably.
• Non-Statutory Technical Standards for SuDS (Defra, 2015)
  • Provide design guidance on runoff volumes, peak flow control and water quality.
  • Used by LLFAs when assessing planning applications, alongside local guidance.
• Schedule 3 of the Flood and Water Management Act (pending implementation in England)
  • In Wales, Schedule 3 came into effect in 2019, making SuDS a legal requirement for all new developments of more than one dwelling or over 100m² of hard surfacing. SuDS Approval Bodies (SABs) must approve drainage before construction starts.
  • The UK Government announced in 2023 that Schedule 3 will also be implemented in England, which became mandatory in 2024.
• Building Regulations (Part H – Drainage and Waste Disposal)
  • Require adequate provision for rainwater drainage and encourage sustainable approaches where possible.
• Local planning policies and guidance
  • Many councils and LLFAs have their own SuDS design guides, which developers must follow in addition to national standards.

In practice, this means that all major developments in England, Scotland, Wales and Northern Ireland must now consider SuDS at planning stage.

Key features SuDS regulations:

1. SuDS have to be incorporated into new developments in England.
2. Applications for the approval of SuDS on new developments that meet the criteria will have to be made to a SuDS Approving Body, or “SAB”, which will sit within the Council.
3. SAB approval will be separate from the Local Planning Authority approval.
4. SAB approval could be subject to conditions and may require a non-performance bond.
5. Construction works covering an area of under 100 sqm or single properties will be exempt. Nationally Significant Infrastructure Projects will also be exempt.
6. Applications for approval could be made to the SAB directly or through the Council combined with the planning application. A fee will be payable and there will be rights of appeal against refusal.

CIRIA C753, commonly known as The SuDS Manual, is the UK’s most widely used guidance on Sustainable Drainage Systems. Published in 2015, it replaced the earlier 2007 manual (C697) and draws on extensive UK and international experience.

The manual sets out good practice for the planning, design, construction, and maintenance of SuDS. It provides practical advice on managing surface water to reduce flood risk, improve water quality, and deliver wider benefits such as amenity and biodiversity. C753 is aimed at designers, engineers, planners, and developers, and is regarded as the national reference point for delivering SuDS that are both effective and sustainable.

The SuDS Manual (CIRIA C753) gives clear guidance on trees and their role in sustainable drainage:

• Tree planting is strongly encouraged as part of SuDS because trees provide natural interception of rainfall, help evapotranspiration, and reduce runoff. They also bring multiple co-benefits such as shade, air quality improvement, and amenity value.
• SuDS design should protect existing trees. This means avoiding damage to root zones during construction and ensuring drainage features are designed to work with root systems rather than against them. The Manual references best practice from groups like the Trees and Design Action Group (TDAG).
• Tree pits can be designed as SuDS components. Permeable paving and engineered soils can allow water to flow into tree pits, providing irrigation while slowing runoff. These systems must include structural soils or geosynthetic layers to prevent compaction and to ensure both tree health and drainage function.
• Integration into streetscapes is highlighted. SuDS standards see trees as an opportunity to combine urban greening with water management, especially along roads and public spaces where they can link to swales, rain gardens, or permeable paving systems.
• Maintenance and species choice matter. Trees in SuDS must be selected to tolerate both wet and dry conditions, and maintenance plans should allow for long-term survival alongside drainage performance.

In short, SuDS standards view trees not just as landscaping, but as integral drainage assets that intercept, store, and treat water, provided they are protected and designed into the system properly.

The SuDS Manual (CIRIA C753) provides detailed guidance on the use of permeable and porous pavements as part of sustainable drainage design. These systems allow rainwater to infiltrate through the surface or its joints, reducing runoff and improving water quality before it enters the ground.

The Manual distinguishes between:

• Porous pavements – where the surface itself is permeable, such as porous asphalt, porous concrete or resin-bound gravel.
• Permeable pavements – where the surface material is not permeable, but water passes through joints, gaps or structural openings, such as block permeable paving.

It also highlights the use of grass and gravel reinforcement systems, which combine load-bearing strength with infiltration, making them suitable for car parks, access routes, or landscaped areas that need to support occasional traffic.

Using geosynthetics in this way supports compliance with SuDS best practice, offering both drainage capacity and durable ground reinforcement.