Increasing Density

Though cities have evolved for over tens of thousands of years, it is the past 140 years where we witness the birth and, in several ways, the rebirth of the tall building now complete. What was historically an anomaly of the urban experience has now become something else entirely. We have now observed a radical density increase across most global cities and with that, an increase and interest in the tall building.

To illustrate this, NYC has seen 60% growth in the number of tall towers completed in the past 30 years (1991-2021) with around 627 new tall buildings. Based on these historic patterns, we can speculate that the share of tall towers may increase by 1,286 by the year 2050 in New York City alone (Fig. 01).  This trajectory can also be seen across other global cities, including Shenzhen, Mumbai and Lagos (Fig. 02).

The Troposphere

Troposphere speaks directly to the first level of the atmosphere, extending from the earth’s surface to a vertical height of roughly 6 miles. In addition, it denotes a new elevated urban understanding of how populations experience density through a city’s upper fabric. This includes a new responsibility for the wall of the tall, supertall, and megatall building as well as a renewed understanding of space and place within the vertical surface.

Historically, the focus on most tall buildings has arguably favored the dual terminus of base and top. This is not to suggest some of our greatest tall buildings have ignored the significance of their façade, but it is to probe that the importance of this tropospheric zone has not only profoundly increased over the past 30 years but will only continue to evolve into a more critical portion of the design of tall buildings as we further densify our urban conditions. Impacts of materiality, scale, environmental responsibility, contextual responsiveness, and place within the vertical surface have the potential to seek new meaning as we further investigate the tall building.

Facade Performance Responsiveness

The need to make high-rise buildings more environmentally responsive has resulted in a heightened sensitivity to the functional priorities of the exterior wall assemblies and components. This focus has become even more relevant as the building industry sets its sights on the goal of carbon neutrality.

In our current generation of work, regulations requiring greater thermal and environmental performance—which are common in many building codes around the world—are influencing our approach to façade design. High performance glass and façade shading devices—well-established measures to limit solar gain—are receiving increased emphasis in an effort to boost building performance. Additionally, window-to-wall ratios to limit the percentages of glazing and reflectivity analyses to control the wall’s influence on nearby properties are influencing the next generation of exterior walls. Similarly, designers continue to invest efforts in sustainable material selections for the reduction of embodied carbon emissions, as well as occupant wellness strategies such as green walls, increased daylighting and light transmission, integration of natural ventilation into the wall, and even measures to minimize bird strikes.

Solidity to Openness

The range of exterior wall strategies from the most solid to the most transparent can be seen in a number of recent projects, each with its own expressive potential.

At the more closed end of the spectrum is the wall of Spring City 66, where its solid elements bend and fold to produce a dynamic surface with plays of light and shadow. This relatively simple gesture allows for a great range of effects in daylight and the opportunity for dramatic lighting at night.

As the wall becomes more open, the use of vertical ribs or fins allows for a high degree of transparency when viewed from straight on, but collapses into a more solid expression when viewed obliquely. This allows both the transparent and solid qualities of the wall to co-exist in a dynamic relationship that changes as one moves around the building.  This effect can be seen in the recent examples of the Shanghai Greenland Bund Centre and the office tower in Kunming’s Spring City 66.

Materiality

While aluminum, glass, and stone continue to be at the core of our exterior wall design palette, we are regularly seeking ways to embellish the fabric of the urban troposphere by exploring richer colors, textures, and materials as part of the exterior wall’s components. In particular, material selection focuses more and more on the reduction of embodied carbon emissions, as fully recycled aluminum framing, low-emission insulation, and engineered timber assemblies become part of the contemporary palette of façade systems.

Occupying the Troposphere

Traditionally, public spaces in high-rise buildings were largely relegated to either the lowest or the highest floors. The desire to extend the vibrant and varied condition of the urban street to those occupying a potentially relentless grid of glass in the sky has driven innovation in programming at higher levels. Now there are greater opportunities for common spaces to be arrayed throughout the building, giving occupants the ability to engage in cityscape views and activity from the mid-levels as well. Occupied roof terraces that occur at building setbacks, such as those on Westlake 66 and the Greenland Bund Center have long been key amenities, but major public spaces are now occurring at multiple points in the height of the building. The Sky Galleries of Zhongmao Financial Center, for example, inject significant and iconic public space at the mid-levels of the towers.