RIDA provides foul water drainage design for residential, commercial, industrial and mixed-use developments across the UK. Our work can cover foul flow calculations, pipe sizing, gradients, invert levels, sewer connection design, pumping requirements and detailed drainage drawings.
We support projects from early planning and feasibility through detailed design and construction information. Public sewer connection work can include design information for Section 106 applications and Section 104 adoption agreements.
A foul water drainage system carries wastewater from toilets, kitchens, bathrooms, utility areas and sanitary fittings to a public sewer, private treatment system or another approved discharge point.
A workable foul drainage design coordinates the proposed building layout, site levels, expected foul flows, connection level, pipe gradients, cover, access points and sewerage undertaker requirements.
RIDA develops foul drainage layouts that fit the site and the wider civil engineering design. The work can start at planning stage with a connection strategy and progress into detailed foul sewer design for construction.
We coordinate with project teams that need drainage support for architects and drainage support for planning consultants, including layout, levels, planning information and technical submission requirements.
Sites with limited fall, deep connection points or restricted routes may need hydraulic checks, a foul pumping station or a rising main.
For wider drainage advice from planning through technical delivery.
For combined foul and surface-water detailed drainage design.
For planning-stage surface-water and foul drainage strategy work.
For surface-water SuDS design and technical drainage proposals.
We calculate proposed foul flows from the development type, occupancy, sanitary fittings and the design basis set for the project. The calculated flow is used to size the network and check available capacity.
Pipe diameters are selected to carry the design flow with suitable hydraulic performance. Checks can cover capacity, depth of flow, velocity, gradients and downstream constraints.
The foul drainage layout sets the network route, manhole positions, pipe sizes, gradients and invert levels. The design is coordinated with buildings, roads, foundations, utilities and proposed site levels.
Inspection chambers and manholes are positioned at junctions, changes in direction, changes in gradient and other points where maintenance access is needed.
For developments connecting to the public sewer, we can develop the proposed connection route, connection level and design information for sewerage undertaker review.
Where gravity discharge cannot be achieved, RIDA can assess pumping requirements and prepare a foul pumping station design and rising main design.
Foul drainage design calculations confirm that the proposed network can carry the design flow through the available levels and pipe gradients.
For larger developments or constrained networks, hydraulic modelling can be used to test network performance under the design loading and assess restricted downstream conditions.
The calculation package can be issued with the drainage drawings as part of the technical design submission.
Foul drainage falls and pipe gradients affect network performance. A pipe set too flat can produce low velocities and a greater risk of solids deposition. Steep gradients can create separate hydraulic and construction issues on sites with tight levels.
The design gradient is set from pipe diameter, design flow, available cover, upstream levels, downstream invert level, access requirements and the receiving sewer.
RIDA sets proposed invert levels and gradients as part of the drainage layout, then checks the network against the project design criteria and approval requirements.
Technical guidance on foul drainage falls, pipe sizes, design flows and foul water drainage regulations can sit in a separate foul drainage design guide. Do not create a second service page for this topic.
Section 106 of the Water Industry Act 1991 covers the right to communicate a drain or sewer with a public sewer, subject to the statutory process and the sewerage undertaker’s connection requirements.
RIDA can prepare foul drainage design information for a Section 106 sewer connection application and coordinate the technical information needed for the proposed connection.
Existing sewer records, invert levels or connectivity may need survey confirmation before the final connection detail is fixed.
A Section 104 agreement can provide for the adoption of newly constructed sewers by the sewerage undertaker. Adoptable sewer design is prepared against the current Sewerage Sector Guidance, Design and Construction Guidance and the sewerage undertaker’s published local practices.
RIDA can prepare foul sewer design information for Section 104 technical review.
For projects with adoptable and private drainage, the design can define the interface between the two systems and the proposed point of connection.
Gravity drainage is preferred where site levels allow a practical connection. A development below the receiving sewer level, or a site with a restricted gravity route, may need a foul pumping station.
RIDA can develop the pumping station design from the proposed inflow, storage requirement, pump duty, static head, friction losses and rising main route.
We review the proposed development layout, topographical survey, available sewer records, planning information and previous drainage work. This stage identifies the likely connection point, available levels and constraints that could affect the design.
We calculate the expected foul discharge from the development and set the design flow used for the network. Phased or mixed-use schemes can be assessed by area before flows are combined.
We set pipe routes, sizes, gradients, manholes and invert levels. The foul network is coordinated with buildings, roads, utilities, proposed site levels and the receiving sewer.
For a public sewer connection, we prepare the agreed technical information and respond to sewerage undertaker comments within the commission scope.
The final issue package is prepared for the agreed project stage, from planning-level foul drainage information through detailed construction design.
The issue package is agreed at appointment so the design matches the planning, technical approval or construction requirement.
The foul drainage information needed at planning stage differs from the information needed for construction. Planning work may focus on a feasible foul drainage connection, expected discharge and site constraints. Detailed design moves into pipe routes, pipe sizes, gradients, invert levels, manholes, calculations and construction drawings.
For larger schemes that need foul and surface-water strategy work at planning stage, see our drainage strategy for major developments.
RIDA can take a project from early foul drainage strategy through detailed foul sewer design, subject to the agreed commission and available project information.
Foul water and surface water serve different functions and normally need separate design checks. Foul drainage carries wastewater from toilets, kitchens, bathrooms and sanitary fittings. Surface-water drainage manages rainfall from roofs, roads, parking areas and other impermeable surfaces.
A project can need both systems at the same design stage, but the design basis, discharge hierarchy, calculations and approval route are different.
For current planning context, see our August 2026 NPPF drainage requirements, the surface water planning data update and our guide to the Flood and Water Management Act 2010.
Kentwode Green, Barnes required a site drainage strategy that integrated new foul sewer pipework and manholes with the wider drainage design. The project is a useful proof point for foul and surface-water coordination on a live development.
RIDA provides engineering-led foul drainage design from planning through technical delivery. Our work is focused on practical layouts, clear calculations and drawings that can be coordinated with the wider project team.
Foul drainage design is the design of the pipe network that carries wastewater from a development to a public sewer, private treatment system or another approved discharge point. It covers flows, pipe sizes, gradients, invert levels, access points and the proposed connection.
Foul drainage carries wastewater from toilets, kitchens, bathrooms and sanitary fittings. Surface-water drainage carries rainfall from roofs and external impermeable areas. The two systems are assessed against different design criteria.
The design flow is based on the proposed development and the design method selected for the project. The calculated flow is used for pipe sizing, capacity checks and connection design.
The foul drainage fall depends on pipe diameter, design flow, available levels, cover and the receiving connection. The gradient is set as part of the network design rather than from one isolated rule.
Section 106 of the Water Industry Act 1991 provides the statutory route for communication of drains or private sewers with a public sewer. The proposed connection still needs to follow the sewerage undertaker's application, notice and technical requirements.
A Section 104 agreement can provide for a sewerage undertaker to adopt qualifying new sewer infrastructure. Adoptable drainage is designed and submitted against the current Sewerage Sector Guidance, Design and Construction Guidance and the undertaker's local requirements.
A foul pumping station may be needed where the development cannot reach the receiving sewer by gravity. The need is driven by site levels, sewer levels, route constraints and the proposed foul flow.
Yes. The scope can include foul flow calculations, pipe capacity checks, gradients, invert levels, hydraulic checks and pumping calculations where needed.
Yes. RIDA can prepare planning-stage foul drainage information and continue into detailed foul sewer design for technical approval or construction.
Send us your proposed site layout, development details and available sewer or drainage information. We can confirm the scope for foul water drainage design, sewer connection work, Section 104 or Section 106 support, pumping requirements and detailed design.
Send us your proposed site layout, development details and available sewer or drainage information. We can confirm the scope for foul water drainage design, sewer connection work, Section 104 or Section 106 support, pumping requirements and detailed design.