In Closing

There are several issues relating to the enclosure system for this building. Because the building will be an adaptive re-use and addition to two existing stone buildings, and because some of the building addition will have to be above the smaller of the two existing buildings, the enclosure system will have to be extremely lightweight in order to not require dramatic structural encroachment upon the existing spaces. Where the new structure interfaces with the old will be a special condition, requiring careful consideration to make it both appear and behave appropriately. The trading floor should be a very open space with minimal interruption from columns; therefore the roof structure needs to be able to span larger lengths (50 to 100 feet). In addition, no direct light or views in from the street should be allowed within the trading floor space for security purposes.
For proposes of this assignment, I will talk specifically about the enclosure system of the new trading floor space itself, since it is the part of the building that requires the greatest amount of special consideration.
One option for the trading floor wall system is a curtain wall. In order to meet the requirement that no direct light or views are present, however, none of the glass of the curtain wall may be transparent. A variety of roofing systems could be used, for instance, a flat truss roof with a bituminous coating or a pitched roof with standing seam metal cladding, but regardless of which roofing system is used the combination of the roof and wall systems would weigh enough to require significant structural interruption of the space in the existing building below.
Another option is to use a tensile fabric structure to enclose the trading floor space. This system could be used for both the wall and roof planes. A fabric enclosure would have the potential to allow diffuse light into the space while remaining lightweight enough to reduce the structural interruption of space below.

If a tensile structure is selected for the enclosure of the trading floor space at the roof and walls, several issues must be thusly considered, including aesthetics, energy efficiency, durability, economy, constructability, and maintenance/service life considerations.
Aesthetically, a tensile structure would be more interesting, and feel even more lightweight, than a steel and glass enclosure. It would represent architecturally the idea or creative innovation that is inherent in the project itself. A steel and glass enclosure is very much the language of modernism, a temporal distinction in architecture that this project seeks to transcend.
Energy efficiency is a major issue for this building; it is an energy exchange, the driving idea of which is that energy, and by extension natural resources, are precious and deserving of our consideration. Because of its large number of occupants and heat loads created by machines in the space, the requirement for conditioning on the trading floor will be for cooling. Therefore, the minimal insulatory value of a fabric tensile structure will be advantageous, as heat will be allowed to escape from the building envelope. In terms of energy performance, a tensile fabric structure seems relatively equivalent to a glass curtain wall, and perhaps better for heat loss than an asphalt or metal roof.
The potential durability of a tensile structure could be called into question. Leaks will happen and can only be delayed, as with any other enclosure system. It is possible, however, to create a system that is not one but two layers, the equivalent of a rainscreen.
Repairs to a tensile fabric wall system would be roughly as difficult to maneuver as to a glass curtain wall, however, the roof repairs would be seemingly more difficult than for asphalt or metal roof system.