Select Page

So what is an “adopted drain” anyway?

Drainage is typically a highly time critical part of any construction project as it is usually one of the last things an architect will consider as part of their design, but the first thing a contractor will want to get in the ground, as it forms the deepest part of the site’s infrastructure. On top of this, the legal agreements required to interact with the public sewer network, or change it, can take a considerable amount of time and money to obtain.

Depending on whether a drainage network is designated public or private has implications for how it is constructed and maintained. A public sewer network – an adopted drain – is one operated by the local water company, with maintenance of the infrastructure paid for through charges to customers, while private drainage is wholly the responsibility of the landowner and their delegates. Private drainage can range from a short lateral connecting a single dwelling with the public sewer, to an entire network, treatment plant and discharge points in a location not served by public sewers.

Agreements between an individual or an organisation and the local water company to make amendments or additions to the public drainage network are administered through several different legal instruments that refer to sections of the Water Industry Act 1991. The four most commonly used are Section 104, 106, 98 and 185 agreements.

Section 104

The Section 104 agreement defines how a drainage network is “adopted” by a water company, adoption being the process whereby a previously private network becomes part of the larger sewer network, with the water company taking responsibility for its ongoing maintenance. The process of adoption should begin before construction commences with the preliminary designs being submitted to the water company for checking to ensure it conforms to the relevant standards, in this case a document called Sewers for Adoption, as well as checking whether the existing network being extended has sufficient capacity to accommodate the additional flows. Sewers for Adoption defines how every aspect of the drainage network should be constructed, including manholes, pipework, and pumping stations, to make the network resilient and the ongoing maintenance straightforward. Once the water company has given technical approval to the submitted designs site inspections will be coordinated between the developer and the water company at critical phases of the construction process to ensure that the work is of an appropriate standard. Once construction is completed a 12-month period elapses where the developer is responsible for the maintenance of the network before the water company takes ownership.

If a drainage network is to remain private the relevant document defining how it should be constructed is Part H of the Building Regulations which is less stringent and more limited in scope than Sewers for Adoption, and can be obtained free of charge through the Planning Portal. The bodies responsible for overseeing the design and installation of private drainage are the local authority’s building control department, and the Environment Agency (or NRW/SEPA/NIEA) if the final discharge point is not into a public sewer.

Section 106

If a single connection is being made to a public sewer with everything upstream remaining private, then a Section 106 is used. In many cases a Section 106 agreement is a more appropriate method by which to connect to a public sewer than a Section 104 agreement. The connection can be made to an existing public manhole, inspection chamber or sewer; if the sewer being connected to <300mm in diameter the pipe will need to be cut and a new T- or Y- junction installed to make the connection, if the sewer is ≥300mm a saddle connection can be used instead.

Section 98

In circumstances where connection to mains drainage is possible, but only via third party land, and an agreement cannot be arrived at between the developer and the owner of the third-party land, then a requisition can be requested from the water company. In essence, a requisition is where the water company uses their statutory powers to create a connection on behalf of a developer.

Usually it is better for both the developer and the owner of the third-party land if a private agreement is arrived at instead, and a connection is made under a 104 or 106 agreement. This a preferable approach as it reduces the cost to the developer, and allows them to offer a larger compensation payment to the third-party landowner than the one they would receive from the water company for the disruption created by the construction work, which is coming out of the developer’s pocket either way.

Section 185

If a proposed structure is to be installed over an existing sewer it will require diversion so that the foundations of the structure do not damage it, either during construction or as a result of the increased loads. A common problem encountered with diversions are a need to cross into third party land with the concomitant legal wrangling that entails, especially if the third-party land is in the public domain, for example a footway or road, or in the hands of a private third-party who is resistant to having extensive excavation work conducted in their land. If necessary, water companies can use their statutory powers to force a diversion in third party land in a similar way to a requisition, but this entails time and financial costs. Another problem encountered is complying with minimum gradients and depths for the diverted pipework, especially if the drainage run being built over is already at a shallow gradient and the diversion, by necessity, makes this even shallower.

In some cases, where there are no other options, a build-over agreement can be obtained where the structure is designed to bridge the pipework, so that the loads are transferred either side of it. Water companies are loath to issue these agreements given the risks involved with construction work around a sewer that is in service, and that the sewer cannot be maintained or replaced in the future through a straightforward excavation.

Please call us on 01984 623404 or get in touch via the Contact Form to talk to us about support with the design and adoption of your drainage.