If you plan to build over, or within three metres of a public sewer, you will need to apply for permission from Thames Water. We can handle all aspects of your application, including structural calculations and architectural drawings. Thames Water needs to assess any building work that may affect its sewers, in order to: Prevent sewer collapse, damage to buildings and possible waste-water flooding, and interruption to drainage from other properties. Ensure that Thames Water staffs have proper access to sewer. The Application Process, although your Local Authority Building Control department is responsible for informing Thames Water about possible building over or near to public sewers, contacting Thames Water beforehand, can speed up Building Regulations applications. Upon receipt of application, Thames Water will carry out a technical review of your plans. If necessary, they will contact you to discuss and agree upon changes to the design before they issue consent. Thames Water recommends that you hire an experienced architect or engineer to ensure that your design complies with their rules and meets their standards. While class I build overs will just be inspected by the Building Control Officer, a CCTV survey/inspection is necessary for Class II and III build overs. When Can't I Get Build Over Permission? Build over permission cannot be granted for newly constructed detached buildings. The same applies if you intend to build over any of the following: Pumping/Rising Mains Manholes Strategic Sewers When build over permission cannot be acquired, Thames Water may consent to the sewer being diverted instead.