The scheme proposed considers the entire perimeter zone of the building in terms of environmental sustainability and a healthy, productive work environment. Walled offices and meeting rooms are kept away from the perimeter of the floor plate to allow circulation along the façade mixed with flexible, unassigned workstations to be used by all workers. Here, access to light and views is a right for all employees.
The extra-large insulated glass façade provides completely unobstructed views and discourages any fixed walls to be framed into it. The façade is also thin and does not occupy valuable rentable floor area. In fact, by removing the perimeter induction HVAC system and replacing it with a ceiling integrated active chilled beam system, floor space has been regained. It is also assumed that the building has been built to the maximum zoning envelope and therefore no external façade elements have been added. Whereas for a different situation, or in new construction, the addition of exterior shading, daylight shelves, or a double or cavity façade might be appropriate, here the thinnest and highest performing skin is proposed to be the optimal solution.
Tenants are looking for amenity spaces. Recladding a building can also be an opportunity to reconsider the line dividing the interior and exterior space. This building’s massing provides a natural opportunity for an elevated terrace and amenity floor. The proposal is to offset the façade inward on the 12th floor to create a covered and open outdoor space, unobstructed panoramic views, and access to plants, flowers, and small trees.
As is with all architectural challenges, a total system approach is necessary to design the singular solution which strikes the appropriate and responsible balance between the conflicting motives.
The extra-large insulated glazing unit (IGU) system proposed here has the benefit of simplicity. Each column bay is enclosed by a single unit which offers unobstructed visual access to the outdoors and allows an abundance of daylight into the space. The height, orientation, and location of the building results in relatively minimal direct solar radiation throughout the year which can be sufficiently mitigated with solar coatings and internal roller shades. The shades are equal in size to the glass unit and at 5% openness they minimize glare but are sufficiently transparent to maintain exterior views while deployed. The increased daylight penetration and elimination of rooms against the façade facilitates a reduced electric lighting load across the floor. The lighting and window shades are controlled by daylight sensors, solar tracking, and vacancy sensors to ensure the most efficient light power density.
The minimal façade framing dramatically reduces thermal bridges and the reliance on error-free field labour as compared to more complex systems. Current state-of-the-art glazing technology includes vacuum insulated glass (VIG) which achieves extremely low conductivity rates within a thin assembly. The unit proposed here is a traditional IGU coupled with a VIG inner lite and includes two coatings to reflect solar radiation outward while maintaining heat radiation inward. The relatively small spandrel area is constructed to maintain a continuous thermal line and filled with mineral wool insulation.
It is insufficient to consider thermal performance alone. The total carbon impact of a building is what ultimately affects our environment. Therefore, it is important to weigh the operational and embodied energy of all building elements. The simplicity of the proposed glazing system is founded in this thinking. Though not quantified for this specific design, it has been found that higher performing and more complex facades which embody more energy or caused more greenhouse gas emissions from the time of resource extraction to its end-of-life do not necessarily have a reduced environmental impact. In other words, a complex system often demands more from the environment than it saves during its service lifetime.
Structurally, the glass resists wind pressures by spanning vertically between floors. To avoid overloading the existing slab edge and perimeter beams, the self-weight is supported as close to the columns as possible and the unit acts as a simple deep beam between supports. To reduce glass thickness and therefore cost and weight, the outer lite is extended below the slab and clamped in a shoe to create a moment-resisting continuous base support. The resulting torsional load is resolved by steel framing between the façade and the perimeter beam as well as the addition of diagonal bracing between the bottom beam flange and slab diaphragm.
Office buildings of this generation are typically heated and cooled with induction systems. These systems run continuously along the bottom 24-36 inches of the façade and utilized relatively small vertical shaftways between floors. The old induction systems lend themselves well to replacement with modern active chilled beam systems because the shaftways can be reused to run the piping for the chilled beams. Coupled with a much more insulative envelope, the temperature gradient near the façade is much less and therefore the demand on the system is far reduced as well.