Our contemporary society has been witnessing a surge in skyscraper construction in urban centers worldwide for various reasons—including engineering advancements, increased urban density, space constraints, and, arguably, a competitive drive for building the tallest structures. The allure of all-glass facades and the pursuit of curtain walls with larger panes of continuous glass have often come at the cost of functionality.
In these towers, operable windows are sacrificed for aesthetics and expansive views, with a central core layout that maximizes 360-degree views while creating architectural "solar heat-gain monsters." Without natural or cross ventilation, these glass skyscrapers trap significant heat from solar radiation within habitable spaces, relying almost exclusively on mechanical HVAC systems to cool these spaces. This raises the question: is passive ventilation strategy becoming obsolete in high-rise design, or can operable systems be integrated effectively into our high-tech towers?
Continuous advancements in glass technology are part of the ongoing skyscraper trend. We've evolved from single-pane rolled glass to float glass and now to multi-layered glass that includes quad-layered systems with various air types within cavities that act as insulators. Modern glass has also improved light transmittance, offering less hue and colorations, becoming near invisible. Similarly, HVAC systems have advanced, with greater power and efficiency, and can manage thermal factors and moisture, which we now understand as critical to occupant comfort. Yet, as we invest heavily in glass and HVAC innovations, are we overlooking other budget-friendly solutions, materials, and strategies that could complement glass while reintroducing operability?
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Glass skyscrapers, in its essence, disregard fundamental orientation principles in building design. Their orientation is dictated solely by the view, as their glass-clad facades are treated as uniform on all sides. This renders any traditional wisdom on building orientation irrelevant. In conventional passive design, building orientation would minimize facade exposure on the west and east to reduce heat gain, favoring more glass on the north facade. However, this approach is irrelevant to all-glass towers, which dismiss basic strategies like using transparency selectively to manage heat gain on south, west, and east facades. This is not to argue that glass skyscrapers should be eliminated, but instead that they can be redesigned to be better integrated into the urban landscape. To achieve this, more passive environmental strategies can be reinterpreted and adapted for skyscraper design, opening the door to a new generation of high-rise buildings that balance operability with high-tech appeal.
Responsive & Operable Facades: Redefining Solar Heat Management in Skyscrapers
One effective strategy to mitigate solar heat gain in skyscrapers, particularly in hot climates, is responsive, operable facades. Incorporating an external shading element in front of the curtain wall glazing limits reliance on the glass and HVAC systems alone for temperature control. These shading elements, which come in various forms, can open or close to balance views with thermal protection. Unlike interior curtains or shades, external architectural shading blocks reflect sunlight before it enters the building, significantly reducing solar heat gain more effectively than interior solutions, which only intercept light after it has entered the space.
One notable example is Plaza 13 by Buesco-Inchausti & Rein Architect, where an additional layer of external shades is positioned before the glazing. This system of box roller external shades offers a controllable, passive way to regulate thermal comfort. It adds character to an otherwise uniform facade through the dynamic, canvas-like shading elements that open and close along thin steel cables.
Operable shading facades have been tested for decades, with Ateliers Jean Nouvel's 1987 Institut du Monde Arabe pioneering the concept in an innovative, mechanical manner, that also draws inspiration from traditional practices. Here, a layer of adjustable apertures—much like a camera's aperture—opens and closes depending on the need for heat insulation over visual views. While located between two layers of glass, this complex system avoided direct environmental challenges like wind load or rainwater, though it proved challenging and costly to maintain or repair.
Despite the maintenance challenges, this aperture system challenged conventional notions of glass skyscrapers, with its geometric, mechanical aesthetic offering a distinct alternative to traditional glazed towers. The influence of this concept can be seen in later applications, inspiring other adaptive facade designs, such as the Al Bahar Towers by Aedas.
The Al Bahar Towers, completed in 2012, pushed the boundaries of operable shading devices on skyscrapers. Their unique facade is a distinctive model of responsive architecture, utilizing shading elements that operate in sync with the sun's path to reduce heat gain and glare. The facades, composed of open and closed triangular elements, break away from the conventional all-glass appearance. Additionally, the shading system's selective application on sun-exposed facades recalls traditional building orientation designs, making it a well-executed blend of modern and time-tested design strategies.
Green Facades and Operable Windows: A Natural Approach to Skyscraper Shading
Another potential strategy for passive climate control is combining green facades with operable windows. By incorporating lightweight planting solutions, such as various types of vines and flowering plants, designers could wrap an all-glass skyscraper with a layer of natural habitat, softening the otherwise austere appearance of curtain wall glazing.
A common criticism of greenery on skyscrapers is the need for soil, which can increase the building's structural load and costs. However, certain plants, carefully chosen and minimally soil-dependent, can avoid these issues. Using planter slots instead of full planting beds can reduce weight, making green facades more feasible for skyscrapers. Vines and foliage, acting as natural shading elements, offer additional benefits like air purification and enhanced thermal and visual comfort within the building. A range of attachment methods allows for easy incorporation of green facades. Techniques include plant guides, stainless steel mesh, and structural frames that support climbing plants, creating a natural shading layer that traditional operable devices cannot replicate.
One Central Park in Sydney, also designed by Ateliers Jean Nouvel, exemplifies green facades as aesthetic features and thermal regulators, filtering sunlight before it reaches the building facade. While green facades may offer less control over specific shading needs compared to operable systems, their soft, organic appearance—enhanced by operable windows and French balconies—creates a scenic, inhabitable environment that no mechanical system could replicate.
In Ho Khue Architects' The Modern Village Office, a mix of local vines, banana trees, and yellow shrubs shields the building's glazed openings, balancing solar heat gain with natural views. Though this project uses more traditional planter beds and opaque facades, it illustrates an alternative green facade application that could inspire skyscraper facade designs.
The conversation around green facades is ongoing, with much to learn from pilot projects that explore this design strategy's strengths and limitations. Issues such as plant maintenance, growth control, and material weathering will continue to shape the future of green facades as a viable strategy for managing solar heat gain in skyscrapers. Whether we can achieve a sustainable version of James Wines & SITE's "High-Rise of Homes" remains an open question, but the potential for green facades to integrate with operable glass curtain walls is promising.
Beyond Glass: Innovating Facades for a Greener, Cooler Urban Future
The discussion around skyscraper facade systems is increasingly critical as urban centers grow denser, often overlooking the urban heat island effect and the high energy demands of HVAC systems necessitated by inoperable glass curtain walls. Rather than accepting these facades as inevitable and depending solely on engineering advancements in glazing and climate control, architects and designers have a responsibility to explore passive design solutions—such as operable shading devices and green facades—to develop facades more suited to the unique challenges of tall, slender buildings with extensive surface areas.
Exhibitions like MoMA's Emerging Ecologies will continue to push this conversation forward, inviting designers to rethink environmentally responsive facades that challenge the conventional glazed curtain wall. These innovations shall aspire to improved comfort, more sustainable building practices, and reduced reliance on mechanical systems for indoor climate control, ultimately supporting a more energy-efficient future for high-rise architecture.
