Except as hereinafter specifically provided:

4.1.

No building shall be erected, converted, enlarged, reconstructed, moved or structurally altered, nor shall any building or land be used, except for a purpose permitted in the district in which the building or land is located.

4.2.

No building shall be erected, converted, enlarged, reconstructed or structurally altered except in conformity with the height, area, parking and loading regulations of the district in which the building is located.

4.3.

The minimum yards and other open spaces, including lot area per family required by this chapter for each and every building existing at the time of passage of this chapter or for any building hereafter erected, shall not be encroached upon or considered as part of the yard or open space required for any other building, nor shall any lot area be reduced below the requirements of this chapter for the district in which such lot is located.

4.4.

Every building hereafter erected or structurally altered shall be located on a lot as defined in this chapter and in no case shall there be more than one main building on one lot except as specifically provided hereinafter.