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By Sara Hart

Above the seventh floor, where the building begins to clear the surrounding buildings, Arup introduced a double-skin facade. Above the noise and carbon monoxide, it exploited the potential for natural ventilation and maximum daylighting, while remembering the client’s instructions to give tenants options. Generally, a double-skin system consists of an external screen, a ventilated cavity, and an internal screen. Solar shading is placed in the ventilated cavity. The external and internal screens can be monolithic glass or a double-glazed unit; the depth of the cavity and the type of ventilation depend on environmental conditions, the desired envelope performance, and the overall design of the building, including systems.

The ventilation in the cavity can be either natural (buoyancy driven), forced (mechanically driven), or mixed (both natural and forced). The direction of the airflow (upward or downward) depends on the type of ventilation and the general system design. The internal screen can be operable for cleaning and maintenance. Depending on the system design, an operable inner screen allows for natural ventilation of the indoor environment.

Two Plantation Place is a separate, but connected, 10-story building—a discrete element of the larger Plantation Place scheme—and it adheres to some of the principles developed for the site as a whole, while establishing a clearly distinct identity for itself. The building is linked through its entrance to established public routes. Its massing is derived from its prominent corner location and the architects’ desire to respond to the surrounding context without losing the building’s visual and functional obligation to the greater whole. The use of load-bearing masonry in the perimeter wall is an innovative approach to the energy-led requirement of minimizing glazed area in similar office buildings. In terms of environmental control, this project is much more complex than the other two. Embedded with wind and photo sensors for natural ventilation, the facades have a certain autonomy because they can operate independently from the other building systems.

These three projects show decisively that “unitized” does not mean “uniform.” Each is very different from the others. Burberry’s strategy was explicitly tied to the craftsmanship associated with the Burberry brand. The designs of George’s Quay and Performance Place, being speculative projects, were driven by client demand for flexibility and energy conservation. In virtually all cases, when “high performance” is the demand, “unitized construction” in a controlled environment will continue to be the answer.