A drainage and SuDS engineer is a specialist civil engineer who designs foul and surface water drainage systems for development sites and ensures compliance with Part H of the Building Regulations and planning drainage conditions. SuDS (Sustainable Drainage Systems) are now the preferred approach for managing surface water run-off on new developments, and most major planning applications require a drainage strategy prepared by a qualified engineer. Their work spans from the initial outline strategy for a planning application through to detailed design for Building Control and sewer adoption.
What they do
- Prepare outline drainage strategies for planning applications
- Design foul and surface water drainage systems to Part H
- Design SuDS features: swales, permeable paving, detention basins, green roofs
- Carry out soakage testing and infiltration assessments
- Undertake hydraulic modelling for surface water attenuation
- Prepare Section 104 agreement submissions for adoptable sewers
- Discharge drainage planning conditions with technical evidence
- Advise on water company and Lead Local Flood Authority requirements
- Inspect drainage installations for compliance with design specifications
When you need one
A drainage engineer is needed for any development requiring a planning drainage strategy or Building Regulations Part H compliance - from single dwellings to major sites.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Outline drainage strategy (planning) | £800 - £2,000 |
| Full Part H drainage design | £1,000 - £3,500 |
| Section 104 submission | £1,500 - £4,000 |
| Hydraulic modelling | £1,500 - £5,000 |
| Condition discharge evidence | £400 - £900 |
| Hourly rate | £75 - £130 / hr |
Water company adoption fees (Section 104 commuted sums) are payable separately and can be significant. Soakage testing and ground investigation costs are also additional to the engineer's design fees.
Frequently asked questions
What is Part H of the Building Regulations?
Part H covers drainage and waste disposal, requiring foul and surface water to be disposed of satisfactorily. New drainage connections must be approved by Building Control. Surface water must be disposed of in order of preference: soakaway to ground, discharge to a watercourse, then discharge to a public sewer.
What is a Section 104 agreement?
A Section 104 agreement is a legal agreement under Section 104 of the Water Industry Act 1991 for the adoption of drainage systems as public sewers. Sewers must be designed to an adoptable standard and inspected by the water company before adoption. The process typically takes 12-24 months.
What is the hierarchy of surface water disposal?
NPPG and Building Regulations require surface water to be considered in priority order: infiltration to ground (soakaway first), discharge to a watercourse, then discharge to a surface water sewer. Connection to combined or foul sewers is only acceptable as a last resort and requires water company agreement.