Special height regulations: In the districts where the height of buildings is restricted to two (2) or three (3) stories, cooling towers, roof gables, chimneys, and vent stacks may extend for an additional height not to exceed forty (40) feet above the average grade line of the building. Water stand pipes and tanks, church steeples, domes and spires, and school buildings and institutional buildings may be erected to exceed three (3) stories in height in residential areas restricted to two (2) or three (3) stories in height, provided that one (1) additional foot shall be added to the width and depth of side and rear yards for each foot that such structures exceed three (3) stories in height.