All buildings and structures shall be subject to height limitations specified in the Schedule of District Regulations except spires, belfries, silos, domes, cupolas, scenery lofts, masts, chimneys, flues, ventilators, elevator penthouses, water tanks, skylights, bulkheads and similar decorative features and necessary mechanical appurtenances usually carved above roof level, provided that the following requirements are met:
(1) The total horizontal area covered by such features shall not exceed 20% of the area covered by the principal structure. Agriculture buildings located on an active farm shall not be subject to the horizontal area limitation.
(2) The excess height of any structure shall not be greater than the shortest distance from such structure to any required yard, nor shall the total height exceed twice the building height limitation in the district in which it is located.