Hello I am looking to build an extension. I have done a bit of research myself, there is a public sewer drain running approximately 1.5 m parallel to the end of the proposed extension. I understand that if I am to build within 3 m of a public sewer, I must get a build over agreement from my local water authority. (the drain is less than 160mm in diameter). The guidance stipulates that for foundations that are more than 1m from a sewer, an angle of 45 degrees can be taken to determine the required footing level. I don’t really understand that, does that mean that I simply take a 45 degree line from the bottom of the foundation, draw a line outwards at that angle, and the sewage pipe must simply be above that line? Also, the guidance stipulates that they prefer to see strip foundations used, but I don’t understand why trench foundations can’t be used? Finally, am I correct in assuming that as a public sewer is effected by the proposal, I cannot go down the route of a building notice and instead must put a full building control application in? The guidance states ‘For work which will be built close to or over the top of rain water and foul drains shown on the 'map of sewers'. Can someone explain that to me?