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By Sara Hart

The structural silicone glazing (SSG) was factory-installed. It was clear in this case that bonding double-glazed units to an inboard aluminum framework of horizontal and stainless-steel vertical mullions was best done in the clean and controllable environment of the shop. Over the past 30 years, structural sealants have earned a reputation for reliability, given that in many cases, such as during earthquakes, they have prevented glass from falling. Structural sealants also protect against other outdoor environmental factors such as sunlight, thermal changes, water, and atmospheric pollutants. “The silicone, therefore, acts structurally to hold the glazing in place, resisting positive and negative wind pressures,” explains Winser. “The vertical load of the glass, however, must always be supported by discreet supports sited along the glass unit’s bottom edge.”

Does unitized construction cost more than stick built? “Not necessarily,” is the answer from Winser. “This procurement strategy is not unusual for preassembled facade systems, as shipping costs are very competitive, and the cladding industry supply chain is fairly fragmented. It is the responsibility of the cladding contractor to organize this logistical network. In Ireland, this challenge is exacerbated by the lack of expertise with this type of preassembled facade system. Hence the partnering arrangement with a U.S. company [Kawneer].”

The hybrid solution

One Plantation Place is a multitenant development in central London, and at over one million square feet, it is unusually large for that part of town. In contrast to the Burberry and George’s Quay projects, the client here, the British Land Company, was very specific about function and maximum flexibility, as it expected to attract up to 70 individual tenants.

The program mandated that Arup Associates, the international engineering firm’s full-service architecture subsidiary, provide the highest quality of internal air quality, with the additional requirement that the design must accommodate the particular needs of a variety of tenants. Facade design, then, played a major role in providing flexibility while regulating the internal environment, which, in addition to air quality, addressed the need for maximum daylight penetration.

 

Plantation Place, London, England Two Plantation Place (above) is sealed and air-conditioned. However, air-conditioning intakes are as high as possible in order to maximize the freshness of the outdoor air. CFD modeling helped determine the environmental conditions throughout the year in both buildings. Blinds incorporated in the wall cavity are opened and closed by local photo sensors. Wind sensors lift the blinds in windy conditions to protect them from damage.

Whereas the facades for Burberry and George’s Quay are best described as unitized high performance, Arup facade engineers chose an unusual strategy for Plantation Place. They created a hybrid curtain wall—or perhaps a series of independent systems—that acknowledges that the environmental conditions existing at street level are different from those at the upper floors. For instance, the base of the building is sealed by a high-performance system and fully air-conditioned. It made no sense to promote natural ventilation where floor plates were too deep for fresh air to circulate through, and where the noise from the traffic would be uncomfortably loud. However, mechanical engineer Michael Beaven notes that, while he assumes the windows will remain closed, they are indeed operable, reflecting a cautious optimism that we may enjoy “silent, clean transport in the future.”