A SuDS designer (sustainable drainage systems designer) is a drainage engineer who designs drainage solutions for new developments that manage surface water through natural processes rather than relying on conventional piped systems. National planning policy and Building Regulations Part H require new developments to manage surface water drainage in a sustainable way - SuDS designers assess the site's drainage potential, test soil infiltration rates and design a drainage strategy that may include permeable paving, soakaways, swales, detention basins, ponds or green roofs. Their designs must meet the requirements of the local lead flood authority or SuDS approval body.
What they do
- Prepare drainage strategies and surface water management plans
- Carry out soil infiltration testing to BRE Digest 365
- Design soakaways, swales, detention basins and retention ponds
- Design permeable paving and green roof drainage systems
- Prepare hydraulic calculations and drainage sizing calculations
- Submit drainage strategies to the lead local flood authority or SAB
- Assess pre-development and post-development runoff rates
- Coordinate drainage with landscape and ecology requirements
When you need one
A SuDS designer is needed on any new development where planning policy or Building Regulations require a sustainable drainage strategy - in practice, almost all new residential or commercial developments.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Drainage strategy report (small site) | £800 - £2,000 |
| Drainage strategy (large development) | £2,500 - £8,000+ |
| Infiltration testing and report | £500 - £1,200 |
| Soakaway design and sizing | £400 - £900 |
| Attenuation pond design | £1,500 - £4,000 |
| SAB or LLFA submission and approval | £1,000 - £3,000 |
| Hourly rate | £80 - £140 / hr |
SAB approval fees in Wales are set by the local authority - typically £350-£1,500 depending on development size. LLFA drainage approval in England is currently handled through planning conditions, with varying requirements between authorities.
Qualifications to look for
MCIWEM is the primary qualification for drainage engineers and SuDS designers. CIWEM is the leading professional body for water and environmental management practitioners in the UK. Members have demonstrated competence in surface water management and drainage design.
Many SuDS designers hold CEng MICE rather than or alongside MCIWEM, particularly those with a civil engineering background. ICE members working in drainage are found through the ice.org.uk member directory.
How to find a SuDS designer
Frequently asked questions
What is a SuDS approval body?
In Wales, the SuDS approval body (SAB) is the local authority body responsible for approving sustainable drainage systems on new developments of more than one property. Developers must submit drainage plans to the SAB for approval before construction and must demonstrate that drainage meets the SuDS standards in the Schedule 3 Statutory Standards. In England outside of London, the lead local flood authority (LLFA) carries out a similar approval role through the planning process.
What is an infiltration test?
A soil infiltration test measures how quickly surface water drains through the ground - used to determine whether soakaways or permeable surfaces will work on a given site. The standard test method in the UK is BRE Digest 365, which involves trial pits dug to the proposed soakaway depth and a standardised fill-and-drain test. A SuDS designer uses the measured infiltration rate to size soakaways and confirm whether ground drainage is feasible.
Do new homes need SuDS?
Yes. National planning policy requires that sustainable drainage should be provided in new development wherever practical. From April 2024 in England, Schedule 3 of the Flood and Water Management Act 2010 requires new developments of more than one dwelling to have SuDS approved by the lead local flood authority as part of the planning process. SuDS must meet national standards for water quantity, water quality, biodiversity and amenity.