Drainage & SuDS Design in Brighton & Hove

Below-ground drainage, soakaways, SuDS and drainage strategies for extensions, new homes and small developments across Brighton, Hove, Portslade, Patcham, Rottingdean and Saltdean. Because we’re structural engineers too, the drainage and foundations are designed together, which matters on Brighton’s chalk.

Get a drainage quote or call 020 3835 2633

Who approves drainage in Brighton & Hove
• Brighton & Hove City Council is the Lead Local Flood Authority as well as the planning authority, so the same council reviews your drainage strategy and decides the planning application. Drainage details are often required through a planning condition before work starts.
• Southern Water is the sewerage company for the whole city. New sewer connections (Section 106), adoptions (Section 104), diversions (Section 185) and building over or near a public sewer all need its approval.
• Building Control checks that the drainage for the building itself meets Approved Document H.

Soakaways on chalk
Most of Brighton & Hove sits on chalk, which often drains well, so a soakaway is usually the first option to test. But chalk can soften, wash out or form voids where water is concentrated, so in chalk we typically keep soakaways at least 10 metres from all foundations, rather than the usual 5 metres in other soils. On a tight terraced plot, that can rule a soakaway out, and we’ll design an alternative, such as permeable paving, attenuation with a controlled discharge, or rainwater harvesting.

The chalk beneath the city is also an important source of drinking water. Much of Brighton lies within groundwater Source Protection Zones, where infiltration needs extra care to avoid polluting the aquifer, particularly from driveways and parking areas.

Other local issues
• Older sewers: much of central Brighton and Hove is served by Victorian combined sewers, which carry both foul and rainwater. Southern Water expects rainwater to be kept out of them wherever possible.
• Terraced streets: shared sewers often run behind or beneath terraces, so rear extensions frequently need a build-over agreement. Build-over agreements explained →
• Steep sites: on the hills of Hanover, Elm Grove and the Downs, getting the levels right, and sometimes pumping, decides whether drainage can reach the sewer.
• Basements: Regency basements sit below the sewer, so they need pumped drainage and protection against sewage backing up in heavy rain.
• Groundwater: in very wet winters, groundwater in the chalk can rise, and parts of the city’s dry valleys have flooded from groundwater in the past. We check this before relying on infiltration.

What we provide
• Drainage strategies and SuDS design for planning applications
• Percolation testing to BRE 365 and soakaway design
• Below-ground foul and surface water drainage layouts for extensions and new homes
• Discharging pre-commencement drainage conditions
• Southern Water applications: sewer connections, adoptions, diversions and build-over agreements
• Off-mains drainage for sites with no sewer, such as package treatment plants and drainage fields, which we specify and coordinate with the manufacturer
• Flood risk assessments where the site needs one
• Structural design for the same project, so the foundations and drainage work together

Our drainage work in Brighton & Sussex
• Rotherfield Close, Brighton: new below-ground drainage for an infill new-build house, and a Section 106 sewer connection application to Southern Water.
• Combermere Road, Hastings: below-ground drainage for a new-build house, and help discharging the planning conditions.
• Meads Court, Bexhill-on-Sea: structural and below-ground drainage design for a mixed-use building.
See our projects →

Common questions

How far does a soakaway need to be from my house in Brighton?
On chalk, we typically keep soakaways at least 10 metres from all foundations, including your neighbours’. In other soils the usual minimum is 5 metres. A percolation test on site confirms whether a soakaway will work and how big it needs to be.

What if there isn’t room for a soakaway?
We’ll design an alternative, such as permeable paving, an attenuation tank that releases water slowly, or rainwater harvesting. Where none of those works, we agree a limited connection to the sewer with Southern Water.

Do I need a drainage strategy for one new house in Brighton?
Usually, yes. Brighton & Hove City Council will normally ask how surface water will be managed, either with the application or through a planning condition.

Can I connect my extension’s rainwater to the sewer?
Only once the options higher up the drainage hierarchy, such as a soakaway, have been ruled out, and then usually to a surface water sewer rather than a combined sewer, at a rate Southern Water agrees.

My extension is over a public sewer. What do I need?
Southern Water’s approval to build over or near it before work starts. We check the sewer records, design the protection or diversion, and make the application.

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Get in touch or call 020 3835 2633