Drainage strategy (SuDS)
A drainage strategy sets out how rainwater and foul water from a new development will be dealt with, usually favouring sustainable drainage systems (SuDS) that slow water down and let it soak away rather than sending it straight to a sewer. Councils often ask for one with applications for new homes, and it can also come up as a planning condition.
This guide covers the rules in England. See Wales, Scotland and Northern Ireland.
0 drainage engineers listed across the UK
Featured (paid) listings first, then A–Z · How we check listings
What a drainage strategy covers
- Surface water: how rain from roofs, drives and paths will be managed, and at what rate it leaves the site
- SuDS features: for example soakaways, permeable paving, rain gardens, swales or attenuation tanks
- Foul water: how waste water will connect to a public sewer, or to a treatment plant if there is no sewer
- Maintenance: who will look after the drainage features once the development is built
When a council asks for one
- The council’s local validation list or pre-application advice says one is needed
- The scheme is a major development, where the local flood authority usually comments on surface water
- The site is in an area with known surface water flooding or sewer capacity problems
- A planning condition asks for drainage details to be submitted and approved before work starts
The usual order of preference
Most guidance asks designers to deal with rainwater as close to where it falls as possible. Letting it soak into the ground comes first, then discharge to a watercourse, then to a surface water sewer, with a combined sewer as the last resort. Whether soakaways will work depends on the ground, which is why an infiltration or percolation test is often needed alongside the strategy.
In Wales, Scotland and Northern Ireland
This guide describes the rules in England. Building regulations are devolved, so here is how drainage strategy (suds) works in the rest of the UK.
In Wales, most new developments need separate approval of their sustainable drainage from the council’s SuDS Approving Body (SAB), as well as planning permission. Check whether the threshold applies to your project before you start work.
SuDS are generally expected for new development in Scotland, and surface water discharges are regulated by SEPA. Check your council’s requirements and Scottish Water’s rules for sewer connections.
Councils in Northern Ireland may ask for drainage details with a planning application, and NI Water deals with sewer connections. Check your council’s requirements.
Common questions
Does my house extension need a drainage strategy?
Most householder extensions do not need a full strategy, though Building Regulations still apply to the drainage itself. Check your council’s validation list if the extension adds a large roof or hard surface, or the site floods.
Is a drainage strategy the same as a flood risk assessment?
No, though they are often done together. A flood risk assessment looks at the risk of flooding to and from the site. A drainage strategy shows how water from the development will be managed. Some councils accept both in one report.
What are SuDS?
Sustainable drainage systems: ways of managing rainwater that copy natural drainage, such as soakaways, permeable paving, ponds and green roofs, so water is slowed down and cleaned before it leaves the site.
Do I need a percolation test as well?
Often, if the strategy relies on soakaways or other infiltration. The test shows whether the ground drains well enough. Your engineer will say whether one is needed.
How much does a drainage strategy cost?
It depends on the size of the scheme, the ground conditions and how much modelling the council expects. Engineers set their own prices, so compare quotes and check what each one includes.
Who approves the drainage?
The planning authority approves the strategy as part of the application or a condition, often taking advice from the local flood authority. Building control checks the drainage work itself. In Wales, a separate SuDS approval is also needed for many new developments.
New to the jargon? See our glossary of terms, from air permeability to TrustMark.