C-1, C-2, C-3, D, OB-1 and OB-2 Districts. For the purposes of this chapter, all buildings in the C-1, C-2, C-3, D, OB-1 and OB-2 Districts shall be construed to be principal buildings. Unless otherwise provided in this chapter, there shall be a distance between buildings of at least 10 feet, but in no event less than the height of the shorter building.