No lot shall be so subdivided or reduced in area as to cause any open space required by this chapter to be less in any dimension than is required for the zone and lot in question.

Where a lot is formed from part of another lot and occupied by a building, such division shall be effected in such a manner as to not impair any of the requirements of this chapter with respect to the existing building or yards and open spaces in connection therewith. No permit shall be issued for the erection of a new building on a new lot thus created, unless it complies with all the provisions of this chapter.