Except as hereinafter provided, no land, building, structure or part thereof shall hereafter be used or occupied and no building, structure or part thereof shall be erected, moved, altered or extended (to expand its exterior dimensions) unless in conformity with the regulations herein specified for the district in which it is located.

With respect to the requirements of this chapter for the district in which it is located, no building shall hereafter be erected or altered:

No part of a yard or other open space about any building required for the purpose of complying with the provisions of this chapter shall be included as part of a yard or other open space similarly required for another building.

This chapter shall not apply to existing buildings and structures, nor to the existing use of any building, structure or land to the extent to which it was legally used at the time of the original enactment of this chapter. This chapter shall apply to any change in use, alterations, extensions or movement to a building or structure, and to any change in use of building or structure, and to any change in use of land subsequent to the enactment of this chapter.