Nothing herein contained shall restrict the height of agricultural accessory buildings such as barns and silos or of the following accessory structures: church spires, cupolas, domes, belfries, clock towers, flagpoles, chimney flues, elevators or stair bulkheads, water tanks, air-conditioning or heating units, stage towers or scenery lofts, or similar roof-mounted rails, parapets, screens or structures, exclusive of utility transmission lines, utility towers, radio towers, telecommunication towers and television towers.