Yard Adjacent to District or Borough Boundary Line. Along any Residence District boundary line or Borough boundary line, a buffer yard shall be provided which shall be not less than 100 feet or two times the height of the building located in the PI District, whichever is greater, in width measured from such boundary line, and in no case shall be less than the required tract perimeter setback. Where a street constitutes a boundary line, the yard shall be measured from the street right-of-way line adjacent to the property.