Chimneys (other than chimneys for central heating plants), flues, ventilators, skylights, towers, bulkheads, water tanks, cooling towers and all other decorative features and necessary mechanical appurtenances and similar features usually carried above the roof level, but excluding telegraph, radio and television transmission or broadcasting antennas, shall be exempt from the height provisions of this chapter, provided that:
The aggregate area covered by all such features, but excluding solar-heating features, shall not exceed 20% of the area of the roof of the building of which they are a part.
The height of each such feature shall not exceed 15 feet above the level of such roof measured at the highest point of such roof.
All such features shall be constructed or enclosed within walls of a material and design deemed by the Planning Board or Building Inspector to be in harmony with that of the main walls of the building of which they are a part.