What is a façade? A façade is a building envelope or the exterior of a building, in laymen’s terms we can say that a façade is a cloth for a building, in the same manner, we use cloths for ourselves to cover our body, keeping us warm, protect us from injures and fashion statement. 3 major types of façades are popular these days: Stick System Façades, Unitized System Façades, and Rain Screens.1) Stick System Façades –
Stick System Facades are a type of façade structure where the mullion (vertical component) is first secured to the slab, and the transom (horizontal component) is connected to the mullion to provide structural rigidity to withstand both the load of the façade and natural loads such as wind pressure, etc. This kind of approach involves on-site manufacturing and piecemeal construction of the building. All types of fabrication in the Stick system are completed on-site, including cutting (which can also be done in a workshop), glazing, and sealing/joining.
Case Study: Spertus institute of Jewish
The Spertus Institute of Jewish Studies is built in Chicago, United States. It was designed by Krueck + Sexton Architects. The area of the building is 13471 m² with 161 feet tall and 80 feet wide. It was built in 2007. The building's exterior surface, mainly the front, resembles an exquisitely cut diamond placed into the wall. The building is an educational institution that operates vertically and has all the facilities of a typical campus, including a café, a shop, a library, etc. Additionally, it contains a meandering top-floor atrium and an auditorium with 400 seats. The building receives a lot of light, and sustainability is taken into account. The roof is designed with heat mitigation and rainwater collection features. The designs are made to be as efficient as possible and encourage the usage of only renewable energy. The building received LEED silver certification as a result of its comprehensive sustainability design. the front elevation of the façade, which is built on a stick system, is composed of 726 separate pieces of glass, each measuring an average of 1320 mm by 2133 mm and coming in 556 distinct forms. A crystalline façade (3D façade) is made out of parallelogram-shaped glass components rather than rectangular ones. 1.375" glass is being utilized insulated with a 0.5" air gap, a 0.5" laminated internal lite comprised of two 0.25" lite laminated together, and a 0.375" low-iron exterior lite (single panel) of glass.To save cooling expenses, a 40% ceramic frit pattern reflects light while dissipating heat [5] and a low-E coating is present on the inner surface of the outer glass lite 0.125" white specks. The modules are installed on Y-shaped aluminium stick-built mullions that span vertically from the floor that flex & twist in accordance with the structure. The current building can save 29% of energy [3]. Innovative design elements were used to preserve the horizontal sound isolation between the slanted glass panes and the vertical sound isolation along the jagged slab edges from floor to floor [6].
The building is valued at $55 million [7]. Given the budget and the aesthetics that the architects wanted to achieve, I believe that the stick system with curtain wall would be the best option. The reason for continuing with the stick system in this building as it is more cost-effective in comparison to the unitized system, the height of the building is low and has less momentum because it is next to another building, which also contributes to the reduction of momentum.
The building would have been more energy-efficient if it had included a thermally broken system. For instance, the product, SG-4-56 from Brital (brital.co.uk) (Image 7) is a thermally broken system. It has an effective U value since it was created for Gulf local climate, and it could be used in this project (the Spertus). The overall U value would be significantly lower with this system if Low-E double-glazed glass was used.Instead of top-to-bottom blinds, I would have chosen ones that go from bottom to top. Mr Davide from CWCT presented this concept during our presentation on heat gain.
If I had been the designer, I would have chosen high-pressure laminate (HPL) rain screens with a metal finish on the exterior surface for aesthetics. With high-pressure laminates, we can improve building performance and sustainability. In addition, the cost of the façade would have been less expensive than the usage of a curtain wall [8][9].
Advantages of high-pressure laminates (HPL) [10]:
· Wide selection of decorative panels
· Optimum modulation with various panel sizes
· UV resistant
· Durability
· Weather resistant
· Resistive to impact
· Panels are extremely resistant to cracking and do not decay.
· In tests conducted at 180° c, mechanical and chemical qualities were unaltered.
· Easy to clean and maintain
· Dimensional stability and flatness
· Lightweight
· Low static electricity, which does not attract dust.
· Quick and easy to assemble
· Minimal maintenance
· No thermal bridge
· Limits heat loss in winter and the transmission of heat in summer
· Overall lightweight substructure and façade
· Can contribute towards BREEAM credit
Unitized System Façades –
The unitized system is an upgraded/advanced version of the stick system. The panels are fabricated and sealed with the frame at the workshop and then delivered to the construction site. It is then hung on the structure of mullions and transoms. When momentum is taken into account, the unitized system is fundamentally more stable. The unitized system is utilized in high-rise structures primarily for this reason: the system may, to a certain extent, move with the building's momentum, which contributes to the stability of the structure.
Case Study: Burj Khalifa
The Burj Khalifa, the tallest skyscraper in the world, is built in Dubai, United Arab Emirates, and it was finished in December 2009. The architects behind it were Skimore, Owings, and Merrill. The skyscraper has 206 storeys and is 828 m in height. Architecture & design criteria, safety, quality, building plan & schedule of work, control procurement, logistics/limited access, working at high altitude/spire work, façade cleaning, and starting & finishing on time were the challenges that were encountered to finish the construction [11] [12]. The cladding panels are comprised of high-performance materials and are particularly constructed utilizing cutting-edge technical methods. The curtain wall will make the structure more recognizable and insulate the inside from outside heat, wind, moisture, and noise. The design is specifically made utilizing cutting-edge engineering methods.The facade is planned as a factory-assembled panelized system, guaranteeing the units are constructed with a high level of precision and uniformity. The geometry of the Desert Flower and the patterning schemes used in Islamic architecture were the inspirations for the Burj Khalifa's design. It blends these historical and cultural inspirations with state-of-the-art technology to create a high-performance skyscraper that will become the new benchmark for growth in the Middle East and serve as a blueprint for Dubai's future development [11].
Aiming to be the tallest building in the world, BURJ KHALIFA's design requirements were out of this world, but they were also full of challenges.
The following facts formed the basis of the design considerations [11]:
· Building movements (Inter-storey drift and sway)
· Thermal consideration to the hot desert climate at 52 degrees Celsius.
· IGU glazing barometric pressure
· Anchor system (with 3-directional adjustment)
· Frame member: mullion with steel reinforcement for high span and higher wind pressure.
· Seismic movement and thermal movement (Stack Joint)
· Water tightness (Stack joint self-drain system)
· Acoustic consideration
· Replacement of glass and replacement of the stainless-steel fin.
· Dead load, lateral load
The following conditions must exist for there to be maximum deflection and stress on the inner pane:
· Maximum wind pressure
· Low-altitude assembly and high-altitude installation
· Low temperature during the assembly and high temperature during the installation.
· High barometric pressure during the assembly and low barometric pressure during the installation. Wind: According to the architectural designs, the structural design of the curtain wall is based on wind pressures ranging from +/-2.0 kpa to +/-5.5 kpa. The façade's air infiltration rate cannot be greater than 1.09m3/h2/m2 at 300pa. With an 828-meter height, the Burj Khalifa is the tallest structure in the world. An aluminium façade with insulated glass modules will serve as the cladding [11].Glass deflection: The maximum centre deflection of all glass at design wind pressure should not exceed 33mm. The calculation is done with the finite element calculation program as a non-linear calculation. Concerning the stress and deflection analysis, this calculation will consider the wind loads, the variation in altitude, the rise in temperature in the glass cavity, as well as the variation in barometric pressure during the assembly and installation on the building.Building movement: Gaskets separate the joints of curtain wall members to prevent metal-to-metal contact and the sound of cracking caused by movement. The joints are designed to meet all performance criteria under a maximum movement of -20 mm and +30 mm. For spans under 4800, the members' deflection restrictions cannot be exceeded by more than Span/175 or 19 mm, whichever is less. Members with spans more than 4800 must not deflect more than Span/240 or 38 mm, whichever is less. the brackets were designed in a manner where a small degree of adjustment and space for momentum for all the axis are available. The space is quite small if we consider just one bracket but if we consider the space available in all the brackets it’s quite a large space to compromise for the momentum of the whole building.Water: No water infiltration should take place at 20% design pressure or up to a maximum of 800Pa. To meet the conditions, lots of physical testing was done. Silicon and custom gaskets were used to weather seal.Water drainage is necessary for addition to water penetration. Given the building's surface size, a well-designed system was created for it since it would be able to endure a lot of rain and storms. As you can see in the image below, in every panel there is a drainage provision and the water is then drained via mullions to the ground.Temperature Range: The façade system is built to withstand the forces of expansion and contraction caused by temperatures of 52ºC and ranging from +2ºC to +54ºC, which might cause the outer wall material surface temperature to surpass 82ºC.3) Rain Screens -
A rainscreen is a specific kind of over-cladding system that consists of a bearing wall, an insulating layer, and a cladding material that is secured to the building with the help of a supporting structure. Because of the way they are built, there is an air space between the load-bearing wall and the cladding material, allowing for constant ventilation and water to drain.
Case Study: **Reliance Mall **I personally visited the site for this project. The building is a four-story retail centre. The façade is made of single-laminate glass glazing and aluminium composite panels, as shown in the pictures above (ACP sheets). The building is located in the Indian city of Vadodara. The initial cost mattered at the time of construction, and the Reliance firm provided the aesthetic design to match the colour red with its corporate brand logo. To let natural light into the structure, a single glass façade was used in the centre. The wall on which the rain screen is built is merely a simple masonry wall; it lacks any type of insulating material to reduce building expenses.