While building some fuel generators I noticed that they use much more space than they should. I couldn't build a fuel generator because always it said "Encroaching others clearance". I had to remove many foundations and walls because they touched the invisible part of the building. You may think it's only the little tower/chimney in the middle of the generator needing space in the height, but in fact it is the complete buildings volume (floorarea x height) and so you can't build in the empty space around the chimney.