Architecture and glass facade

Glass Façade

Introduction

Glass is becoming an essential component of many facades. This material is easily shaped and installed, allowing for the creation of gripping and dominating structures. However, a contemporary construction must meet a number of criteria in addition to esthetic standards to create enough comfort within a structure. It is vital to imagine a structure with an “interactive” shell to improve occupant comfort by increasing the quality of interior space and optimizing natural resources[footnoteRef:1]. Modern glass constructions have progressed from single-layered framed window glazing to load-carrying, high-performance structural elements that significantly impact modern architecture’s aesthetic attributes. Due to the complexities of using glass elements in modern buildings, several façade consulting considerations must be made to achieve a high-quality solution[footnoteRef:2]. Therefore, this paper seeks to determine the various attributes of glass facade and further elaborate the discussion by case analysis of The Shard glass facade. The discussion will cover why glass is used in facades, the history of using glass facades, the benefits and attributes of glass facades, and the sustainability features. [1: Jelena Savi?, Danijela ?uri?-Mijovi?, and Veliborka Bogdanovi?. "Architectural glass: Types, performance and legislation." Facta universitatis-series: Architecture and Civil Engineering 11, no. 1 (2013): 35-45.] [2: Muhammad Tayyab Naqash, Antonio Formisano, and Ehsan Noroozinejad Farsangi. "Structural assessment of glass used in façade industry." In Structures, vol. 33, pp. 4817-4827. Elsevier, 2021.]

Background

Glass is one of the earliest manufactured materials that has been used continuously since its inception. Although the exact period of glass history is unknown, the earliest date discovered is 7000 B.C., during the Neolithic period. It was first employed in Egypt for decorative purposes before 3000 B.C., primarily as a colorful glaze on stone, pottery, and beads, but Romans pioneered its use in windows[footnoteRef:3]. A glass facade must have coincided with the change from conservative brick and concrete wall to a curtain wall. In the early years of the 19” century, there was a progressive shift away from traditional load-bearing masonry toward a framed structural system with steel and concrete parts[footnoteRef:4]. This gave rise to the possibility of replacing a masonry facade wall with a lightweight, transparent one. Because the facade on framed constructions no longer had a bearing duty, the facade wall took on the job of a façade window. The development of lightweight facade systems began and progressed simultaneously with the development of the skeletal system. [3: Alice T. Friedman, American Glamour and the Evolution of Modern Architecture. New Haven, CT: Yale University Press, 2010.] [4: D. D. Mijovic, D. Milanovic, and S. Jelena. "Curtain walls: history and a continuing challenge." In XVIII Int. Sci. Conf." Construction Archit. VSU 2018, pp. 1-6. 2018.]

The Crystal Palace (figure 1 below), built by Joseph Paxton in London in 1851, heralded a shift in architecture’s customary opaqueness by introducing transparency through the glass. He took glass from the greenhouse into the architectural domain for the first time. One of the main goals of this project was to create a consistently lighted indoor area using daylight as the sole source of light. As a result, translucent screens of calico were hung externally in-between the ridge beams of the roof glazing. They covered the whole surface of the highly exposed horizontal section of the roof to reduce the harsh sunshine and glare caused by this excessive transparency.

A

B

Figure 1: The Crystal Palace in London, 1851, shows glass façade, (A) Exterior and (B) Interior. Adopted from Mijovic, Milanovic, and Jelena[footnoteRef:5] [5: Ibid, at 2]

The idea of transparent, all-glass buildings piqued the interest of architects. Chicago architects constructed America’s first high-rise glazed building in the first half of the twentieth century. At the same time, Ludwig Mies van der Rohe of Germany envisioned and crafted models of hypothetical 20 and 30 story skyscrapers clad entirely in glass, resembling buildings today. Technology didn’t allow for the building of multi-story glass facades like those on Bunshaft’s Lever House and Mies van der Rohe’s Seagram Building and the many other glass skyscrapers that make up Manhattan’s skyline until the middle of the twentieth century.

Benefits for glass façade

A glass façade provides a strong and weather-resistant exterior for the building. While some people may not realize it, the materials used in glass facades are exceptionally sturdy and long-lasting. They’re built to withstand severe weather, such as heavy winds, rain, snow, sleet, and everything in between. Glass will not only repel these elements, but it will do so without altering its appearance. Unlike some other materials, it does not rust or otherwise erode due to exposure to the elements; thus, it will not be a problem for those constructions that employ glass.

A glass façade has a major benefit in delivering green buildings and conserving energy usage, especially lighting[footnoteRef:6]. This benefit is especially appreciated in large buildings where a significant fraction of energy consumption is in lighting. With a glass façade, a building will use the sun’s natural light to light up the building’s interior. In huge constructions, contemporary glass is amazing at managing temperature. It’s wonderful to assist businesses in meeting the stringent commercial energy use standards. It’ll become much more popular in the coming years as these regulations tighten in response to public demand. These two properties of glass can save a lot of energy that would otherwise be utilized for artificial lighting and temperature control. [6: Constro Facilitator, “Glass facade; An overview of advantage and types.” 2021, December 7. ]

The other and probably the most important benefit of glass façade is the aesthetic value it confers to a building. Glass facades are some of the best-looking solutions available, in addition to being functionally strong and incredibly beneficial in a variety of practice areas[footnoteRef:7]. Glass building facades give off a sleek, modern vibe that appeals to a wide range of potential customers. The customizable pieces allow architectural designers to create any design building-owners choose, resulting in a modern aesthetic that will stand out from afar and up close. [7: Ibid]

Shortcomings of glass façade

Due to the high temperatures required for processing the raw materials, glass manufacturing is a very energy-intensive operation. Compared to the other materials used in construction, glass is a costly material. As a result, the overall cost of the structure may rise.

Glass is a fragile, stiff, and rigid material. When put under stress, it snaps without causing undue strain. As a result, glass is less impact-resistant, and its ability to endure an immediately applied load is limited. When it comes into contact with an object, it will immediately break. Glass is extremely hazardous in earthquake-prone areas[footnoteRef:8]. Unfortunately, there has been no technological innovation that can make Glass an earthquake-resistant material. It can, however, be adjusted to a degree so that it can resist small-scale earthquakes with some pricey treatment. Finally, broken glass can be exceedingly sharp, increasing the risk of injury. [8: Mehran Arbab and James J. Finley. "Glass in architecture." International Journal of Applied Glass Science 1, no. 1 (2010): 118-129.]

Types of glass used in facades

Curtain wall

Curtain walls are non-load bearing curtain-like constructions linked to the building’s floor where the façade will be installed. Such facades must only support their weight, not the dead load imposed by the structure[footnoteRef:9]. The curtain wall is connected to the building’s columns and floors, allowing the weight of the wind to be transmitted from the façade. Wind and water resistance are provided by these sorts of facades, which are aesthetically beautiful and useful. Glass facades give resistance to seismic stresses and are a heat barrier. [9: AISwebapp, “AN ARCHITECT’S GUIDE TO GLASS FAÇADE.” AIS, (2020, Feb. 1) < https://www.aisglass.com/an-architects-guide-to-glass-facade/>]

Figure 2: Curtain wall glass facade. Adopted from Constro Facilitator[footnoteRef:10] [10: Constro Facilitator, “Glass facade; An overview of advantage and types.” (2021, December 7)]

Storefront wall

This is another non-load-bearing façade that is predominantly used on the bottom floor. When constructed with specialized glasses, it extends between the ground and the roof of the building above it, providing maximum thermal and acoustic insulation. It is a cost-effective alternative that may be tailored to the client’s preferences.

Figure 3:Storefront wall glass facade. Adopted from Constro Facilitator[footnoteRef:11] [11: Ibid]

Framing systems

1. Stick systems

Vertical support mullions frame these sorts of glass facades. These extrusions are normally built wholly away from the installation location. The mullions are then transported to the construction site and installed glass panels. Vertical extrusions are typically supported by horizontal frames, resulting in glass framed on both sides. The mullions used in stick systems are often formed of aluminum, steel, concrete, or wood. All of these materials can be used, depending on the stylistic preference. Because of their high prices, structured silicone, toggle-locked, bolted, or pressure-capped stick systems are used in mid-rise or low-rise buildings.

Figure 4: Stick system glass facade. Adopted from Constro Facilitator[footnoteRef:12] [12: Ibid]

1. Unitized system

As the name implies, such glass facades are often manufactured in a factory and then transported to the installation location. This means that unitized systems arrive at the building ready to be installed. In tall buildings, the continuous system might span numerous floors. Unitized-framed facades can also have vents and windows fitted. Because the complete framing system is built in a factory under regulated climatic conditions, elements such as moisture and air resistance may be included. The completed systems are typically transported to the site using mobile street cranes, tower cranes, or monorails.

Figure 5: United system glass facade. Adopted from Constro Facilitator[footnoteRef:13] [13: Ibid]

1. Semi-unitized system

Semi-unitized systems combine the best characteristics of both stick and unitized systems. This sort of glass facade is encased in a stick-made aluminum cassette. At the plant, the glass is filled into the cassettes. Individual cassettes are then transported to the construction site and assembled with other cassettes. Gaskets seal one metal casing to another, allowing for quick and safe assembly and installation. Structural silicone is required for these types of systems during the installation procedure.

Frameless system

Frameless glazing is an effective approach to increase the amount of natural light transmitted through a structure while minimizing the impact on both the internal and external aesthetics of the glass structure.

Figure 6: frameless facade. Adopted from Constro Facilitator[footnoteRef:14] [14: Ibid]

Tension system

These facades use high tension cables or stainless steel rods to put weights on the main structure. As a result, the amount of solid structural parts visible on the project is reduced, boosting the facade’s transparency. Tension rod facades and cable net walls are the two most used forms in the industry.

Figure 7: Tension glass facade. Adopted from Constro Facilitator[footnoteRef:15] [15: Ibid]

Sustainability of glass in buildings

Glass is a long-lasting, entirely recyclable material with numerous environmental benefits, including helping mitigate climate change and conserving natural resources. Glass is 100 percent recyclable and does not degrade while being recycled. Consequently, it can be recycled multiple times without sacrificing quality or purity. Its inert nature and commitment to safeguarding the health and well-being of inhabitants are likewise highly valued in many applications[footnoteRef:16]. However, the widespread use of glass in buildings may work against worldwide attempts to create sustainable and green structures. Most experts agree that glass façade buildings do not match most climates because they need a lot of energy to cool and heat. Because heat is transported to the exteriors very slowly, opaque walls result in decreased energy use. [16: N. Sudharsan, T. Palanisamy, and S. C. Yaragal. "Environmental sustainability of waste glass as a valuable construction material-A critical review." Ecology, Environment and Conservation 24 (2018): S331-S338.]

Case study of The Shard

The Shard is a mixed-use structure. It’s designed to be a vertical metropolis where people can live, work, and relax. One of the Shard’s most distinctive features is open vents between sloping glass faces. The visual quality and shape of the tower are defined by eight “splinters” of glass. The massive 36.000M2 double ventilated façade uses low-iron crystals with a mechanical roller blind in the hollow to give sun protection[footnoteRef:17]. 11,000 glass plates were utilized to coat the walls, providing natural ventilation to the winter gardens. Many of these are slanted solar panels properly oriented to the sun deck, resulting in a wide area of renewable energy. [17: Leslie Tijerina, A. Silvas, H.J.A. Mahmoudi, S. Sadri & B. Yaghmaei. “The Shard at London Bridge.” ARCH-631 (Fall 2016). ]

A single skin on the outside and a sealed double-glazed unit on the interior were used to create triple-glazed panels. As “wing walls,” the shards were extended beyond the margins of the floor plates, giving the individual façade planes more visual character. Each floor level has a 300 mm wide outside chamber that is aired. When the sun heats the air in the cavity, it rises and escapes out the top of the panel’s vent, pulling cool air in at the bottom[footnoteRef:18]. A roller blind is also installed in the cavity, controlled by the building management system (BMS) to limit solar gain further. Users of the shard can raise a blind to see the vista, but the BMS lowers it after a brief time. [18: Ibid]

Use of glass façade

The tower boasts all-glass facades on all four sides, with 11,000 façade pieces totaling 80,000 square meters of glass[footnoteRef:19]. The Shard’s panels are comprised of low-iron glass with internal blinds, which provide additional external strength to the skyscraper. Furthermore, the glass facade helps maximize daylight, attain the highest BREEAM certification for the building (which examines and verifies its sustainability), and improve the working environment for staff. Moreover, the Shard’s glass exterior offered more visual value to the London skyline. As a result, architectural engineers have characterized the structure as a lovely addition to the London skyline. [19: “The Shard,” Permesteelisa Group, (n.d.). < https://www.permasteelisagroup.com/project-detail?project=791>]

Justification for the glass façade

Design, architectural, and technical criteria

The primary features that the glass façade brings for The Shard are high performance and transparency. The Shard’s plan is an irregular, eight-sided polygon, with each glass segment, or ‘shard!’ sloping in a different direction and being exposed to the sun differently. The eight glazed facades gradually taper as they approach the building’s top. They resemble a massive deck of cards, with each layer tilting inwards at different angles. The unique characteristic of this glass castle is that the shards never come into contact with one another, allowing the wind stress on broad stretches of converging flat glass surfaces to be avoided. A double-skin facade is created by wrapping an inner curtain wall around the structure, filling in the spaces left by the outer fragments. The ‘fracture’ sections, where the external shards shattered, are occupied by winter gardens and conference rooms.

The Shard’s asymmetric volume required a highly sophisticated glazed envelope design. Around 11000 units were designed, engineered, manufactured, and installed across the eight ‘shards,’ many of which were one-off production elements. The Shard’s envelope is a double-skin passive system. This was required to meet the exceptionally high transparency requirement, which would have been impossible to achieve with an active double-skin facade with a mechanical ventilation system. The envelope’s beauty comes in its complexity, as it is far from a straightforward design with numerous execution obstacles.

Aspects of the buildings

The other justification for using the glass façade was the prominent position The Shard occupies in the London Skyline and the London landscape. The structure is among the tallest buildings in London, and thus, there was an architectural need for the structure to present the skyline with the aesthetic value it needed, thus making a glass façade the best option. Second, the structure is located in the neighborhood of the London Bridge, the Westminster Hall, and the Parliament Building. These structures hold a prominent position in London’s structural and architectural image of London and the U.K.; thus, it would go without saying that the visual value that comes with a glass façade was justified.

Disadvantages and advantages

The primary disadvantage of The Shard’s glass façade is that the exterior surface of the façade has to be cleaned manually, considering there are 11,000 panels of glass. This is a security concern for the glass cleaners, especially bearing in mind the cleaner who was left dangling on the 72nd floor when his cradle developed a mechanical fault due to high winds, a few days to the official opening date.

Despite this concern, the futuristic glass casing of the structure is triple-glazed and low-iron laminated, meaning it has a colorless low emissivity that reduces infrared heat loss. Computer-controlled roller blinds eliminate the need for air conditioning to avoid excessive heat buildup from solar energy. These glass fiber blinds are integrated into the glass facade and covered by single glazing, lowering solar radiation by 95%[footnoteRef:20]. When night falls, the blinds are rolled up to enable the day’s heat to escape. The Shard’s passive sun-shading mechanism has helped it to exceed the Part L directive’s 2006 standards by more than 25%. [20: Ben Hoskin, “How the shard was built and the problems they faced.” (n.d.).]