Within the restricted residence district there shall be a front yard of not less than twenty (20) feet (measured from the front lot line), except as follows:

   1.   Between Existing Buildings. Where a building is to be erected on a parcel of land that is within one hundred (100) feet of existing buildings on both sides, the minimum front yard shall be a line drawn between the closest front corners of the adjacent buildings on the two (2) sides, or

   2.   Adjacent to Existing Building. Where a building is to be erected on a parcel of land that is within one hundred (100) feet of an existing building on one side only within the same block, such building may be erected as close to the street as a line drawn from the closest front corner of that building to a point twenty (20) feet back from the front lot line measured at the center of the lot on which the proposed building is to be erected.

   3.   Double Frontage. Where lots have a double frontage, the front yard as required herein shall be provided on both streets.