What do you do when a manhole is in the way of your extension? My last two projects have been afflicted with the problem of public sewers running across the property – right in the way of the project.
The answer is simple. You need Sewer Build Over permission granted by Thames Water. If your proposed development comes with in three (3) metres of the pipe then you need permission to build near it. It may sound strange, and you may argue that it’s your property, however if you check the paperwork and title deeds from the sale all will be clear.

Thames Water owns and is required to maintain and have access to the pipes as long as they are connected to their network of sewers. To build over or near their sewers you then require their agreement in writing, which must be passed on when the property is sold. This agreement assures Thames Water that the foundations of the new development does not impact the sewer system. Building Surveyors will ask to see the agreement before they sign off the Completion Certificate. Extra weight from the foundations can cause the sewer to collapse and cause waste water flooding which may cause structural damage to the nearby building. To prevent further damage to sewers and buildings and to reduce disruption to waste water services, the new building may have to be knocked down. Thames Water will not allow you to build a new detached property over a sewer.

In this case, a sewer diversion (at your cost) is required, but it must be built to Thames Water specifications. These public sewers are in three (3) classes and three (3) different sizes which require different application processes and different fees. Class I is 160mm diameter or smaller, Class II is greater than 160mm, but less than 375mm and Class III is greater than 375mm diameter. For Classes II and III, a CCTV camera survey is required inside the pipe before work can commence. This is to ensure that no repair work is required, and is repeated after to confirm that the works have not damaged the pipe.