Civil Engineering London: Drainage, SuDS, Retaining Walls and Infrastructure

Homeowners and developers needing below-ground drainage, SuDS or retaining wall design for an extension or new build; architects requiring civil engineering input to support a planning submission; and contractors coordinating sewer build-over agreements or external works. If your project involves ground levels, water, drainage, retaining structures or utilities, it needs civil engineering input alongside the structural design.

We design below-ground foul and surface water drainage systems sized and laid out in accordance with Building Regulations Part H. Drainage runs are coordinated with the foundation design so that trenches, inspection chambers and connections do not conflict with the structural frame. Where discharge is to a public sewer, we provide the information needed for the water company connection agreement.

Sustainable Drainage Systems (SuDS) manage surface water at source rather than discharging it to an overloaded sewer network. Planning applications for larger residential developments and most commercial schemes are now expected to include a SuDS strategy.

We carry out infiltration testing and soakaway design to BRE 365, calculate storage volumes for the design storm event, and prepare the SuDS strategy report that supports the planning submission and the subsequent drainage condition discharge.

Retaining walls are designed to Eurocode 7, with stability checks against sliding, overturning and bearing. We design gravity, cantilever and reinforced concrete retaining walls, as well as masonry garden walls where the retained height makes them structural rather than decorative. Where a retaining wall is close to a boundary or supports a neighbour's ground, the design also addresses party wall considerations.

External works include hardstanding for vehicle loads, paved areas, levels and the interface between the building and the external ground. We design external slabs and hardstanding for the anticipated loading, coordinate the falls and drainage, and integrate the external works with the below-ground drainage design.

Where a public sewer runs within three metres of proposed foundations, a build-over or close-to agreement with the sewerage undertaker is normally required. We prepare the structural and civil engineering information the water company needs, including the foundation design in relation to the sewer, protection measures and method statements, and we manage the technical correspondence through to approval.

Residential and commercial developments frequently interface with existing infrastructure: public sewers, water mains, highway drainage and adoptable roads. We coordinate the civil engineering elements with the wider utilities and highway authority requirements, including Section 38 and Section 278 technical approval where relevant, so that the below-ground design is consistent with what the adopting authority will accept.

Civil engineering does not sit in isolation. Drainage trenches, retaining walls and external levels all interact with the structural foundations and frame. We hold both disciplines in-house, so the drainage layout and retaining wall design are coordinated with the structural design from the outset, reducing the risk of clashes, rework and Building Control queries.