No multiple dwelling shall exceed six stories with a maximum height of 65 feet, except that this height limitation shall not apply to ventilators, skylights, water tanks, bulkheads or similar features, a radio and television antenna installation for the use of all of the residents of the multiple dwelling, a swimming pool and/or solarium for the use of all of the residents of the multiple dwelling and necessary mechanical appurtenances usually carried above the roof level. However, such features shall be erected only to a height necessary to accomplish the purpose it is intended to serve, but in no case more than 14 feet above its lowest point of contact with the roof. Chimneys will be permitted to exceed the fourteen-foot height limitation. The total area covered by such features exempted from the height limit, except recreational facilities, shall not exceed, in cross-sectional areas, 25% of the area of the roof on which they are located. All such features shall be enclosed within walls of material and design in harmony with the main walls of the building on which they are located, except in the case of a swimming pool or solarium where no enclosure is required.