I am in the process of digging out footings for a double storey side extension. There is an existing manhole in my side driveway which my neighbours foul waste passes through and on into my other neighbours property. I had intended to install a double sealed manhole and tile it into the floor of my new utility room. My builder contacted Thames Water who advised him that the manhole must be relocated outside the property a minimum of 200mm from the boundary and 500mm from any new walls. Add to this the 450mm or so for the actual manhole and I have lost almost half of my proposed 2100mm extension. Please see the attached plans. Any thoughts or experiences gratefully received.