First ask whether diversion is necessary
Compare the verified sewer route with the proposed building and foundations. A change to the building layout may avoid the asset, while some work to an existing property may be assessed through a build-over agreement. New development and particular sewer types can need a different approach. [2] [3]
Thames Water's guidance says that new properties should use a diversion route rather than assume a build-over agreement is available. It also identifies special restrictions for strategic sewers and rising mains. Raise those matters before assuming that any pipe can be bridged beneath the development. [2]
Understand the statutory route
Thames Water's diversion guidance refers to section 185 of the Water Industry Act 1991 and the position of a person with an interest in land proposing development or improvement. The company assesses the request and the diversion arrangements. This is not permission for the landowner's contractor to alter the public network without approval. [1]
Where the project involves another owner's land, identify the issue at the outset and obtain the required agreement through the proper process. A line drawn outside the site boundary does not establish a right to construct or maintain the proposed sewer there.
Information needed for feasibility
Provide the existing sewer position, the proposed building arrangement and the suggested diversion route. Establish pipe size, levels, connections and the space needed for maintenance access. Use the water company's asset records and an appropriate site investigation rather than designing only from an assumed route. [4] [2]
Ask Thames Water which design, construction and checking responsibilities will sit with it and which may be undertaken by your appointed team. Its published process describes routes involving developer-arranged work as well as company involvement. [1]
Budget and programme
The charge depends on the agreed work and the company's current charging arrangements. Do not substitute a simple build-over application fee for the cost of constructing a diversion, arranging access or completing associated checks. Thames Water publishes a separate developer-services charging framework. [5] [6]
Request a written scope, payment arrangement and programme after the feasibility requirements are understood. The programme and cost will differ between a straightforward local alteration and a complex public-network diversion.
Coordinate the final approvals
Reflect the approved route in the structural and drainage design, agree inspections and surveys, and retain the completed records. Building control drainage requirements and the sewer owner's consent are separate matters; both need to describe the same proposed work. [7] [1]