No building shall exceed a height of 30 feet. Height limitations of this section shall apply to chimneys for central heating plants and antennae, if any, but shall not apply to ventilators, skylights, bulkheads, building chimneys, water tanks, cooling towers, necessary mechanical appurtenances, and similar features related to the functioning of the building and usually carried above the roof level, provided that:
A. The aggregate area covered by all such features shall not exceed 25% of the area of the roof of the building on which they are located;
B. The height of each such feature shall not exceed 15 feet above the level of such roof; and
C. Such features as water tanks, cooling towers and bulkheads shall be enclosed within walls of a material and design in harmony with that of the main walls of the building of which they are a part.