The height and setback regulations of the designated Residence and M1 Districts shall not apply, except for permitted obstructions pursuant to Sections 23-62 or 43-42, as applicable. In lieu thereof, all buildings or other structures shall comply with the regulations set forth in Sections 117-531 (Street wall location) and 117-532 (Setback regulations for buildings that exceed the maximum base height). Such regulations, however, shall not apply along the street frontage of that portion of a zoning lot occupied by existing buildings, unless the street walls of such existing buildings are vertically extended by more than 15 feet. The height of all buildings or other structures shall be measured from the base plane.