A curtain wall is a wall that encloses a space within a building but does not support the structure in any way. It is the outer covering or skin of a building, in which the outer walls are non-structural but merely keep the weather out and occupants in. As the curtain wall is a non-structural cladding system for the external surfaces, it can be made of a lightweight material thus reducing construction cost. The most popular material used for this is glass which suffices not only creating an enclosure but lets the light in and therefore, creates large and uninterrupted areas with clear passage of light.
Other materials that can be used are Aluminium Composite Panels (ACP), metal panels or even thin stone, thus creating an attractive facade of a building whenever required. These materials, especially ACP and glass, are available in a wide spectrum of colours and choices.
The Story and Significance
English architect and civil engineer, Peter Ellis built Oriel Chambers (1864) and 16 Cook Street (1866) both in Liverpool, England. These two buildings are credited as the first curtain walls utilizing glass. Aluminium framed walled systems started developing rapidly after World War II, sometime during the 1930’s when the production and supply of aluminium became readily available. They became a cost-competitive and cost-effective alternative to other facade treatments. ACP was extensively used in the later part of the 20th century onwards, and soon became a staple of the modernist movement of which we all know so nostalgically: Bauhaus school, Hall Idie building, Seagram’s building etc.
But the real roots of curtain walls lie much more deeply within the fabric of not only architecture but even within the very psyche of the massive societal renaissance, transforming the world during that time (late 19th century) , which eventually blossomed into the modernist movement. During this intellectually tumultuous time, thinkers and philosophers rejected the certainty of enlightenment thinking and any religious beliefs. Modernism promoted the recurring critique of previous traditions and beliefs in various fields, advocating self-consciousness and experimentalism while incorporating individual expressions of humanism a.k.a what it means to be human. In short, modernism emphasized on improvement of the human condition (the user).
How the origin of the curtain wall is related to this broad movement? Curtain walls are symbolic of modernist experimentalism as for the first time architects and engineers toyed with the idea of doing away with traditional load-bearing walls since antiquity, which heavily reduced the flexibility of occupancy and focused more on the structure than the users. Instead, they started to experiment with beam and column structures which offered unprecedented flexibility of occupancy; for the first time, a building could have multiple functions suited to the changing needs of users.
For the first time, buildings could represent the dynamic conditions of a user instead of just an institution, religion, state or an abstract ideology. This particular structure warranted a suitable replacement for the wall. It now served as a portal merging the interior and exterior. Any innovation in the field of architecture is intrinsically tied to the user, the human being, right from its genesis throughout its lifespan. A curtain wall is one such innovation.
Anatomy and Installation of the Curtain Wall
Typically a curtain wall system comprises a spectrum of facade design. The various infill panels that can be used are various kinds of glass, aluminium or other light-weight metals, stone veneer, fibre-reinforced plastic, aluminium composite panels, louvers or vents and GI fabricated “jaali’s”.
These panels of curtain walls transfer the load back to the primary structure of the building as well as provide thermal insulation to it. They add to a stronger visual impact of the building but at the same time need regular maintenance and cleaning.
Adequate access systems for tall buildings are needed for regular inspection. It definitely creates a dust barrier for the building. They can be classified by their method of fabrication and installation into two basic categories: The Stick System, where the curtain wall frame and panels are installed and connected piece by piece on site, and, TheUnitizedSystem -where the entire curtain wall is fabricated and assembled in the factory before shipping.
The unitized system is limited to a typical module size of 5-6 ft. Both these systems are essentially with glazed panels. In the case of tall buildings, they are installed from the internal side. Careful integration with other elements such as wall claddings, roofs etc. is required for a successful installation.
The success of a curtain wall system depends on its effective ceiling, thermal performance, moisture protection, sound insulation and visual appearance. Any curtain wall system should be designed to collect any condensation on the exterior side. Careful detailing and designing of the curtain wall prevents any movement caused by thermal changes and wind pressure, therefore, the connections to anchor it to the building structure should be designed so as to allow differential movements.
This should be very well taken by good quality glazing gaskets which shall prevent the movement of glass within the frame.
Another very important aspect is fire safety. If designed well, these glazed panels offer easy access for firefighters. But they may trap smoke and poisonous substances within the enclosed space. So, curtain walls can play both the tormentor and saviour in case of emergencies.
The most common method of installation is a lightweight aluminium frame with infill panels made of glass fixed to the frame. This can be custom-designed and manufactured according to the colour, shade and tint thereby offering a wide choice of façade design.
Designing of the Curtain Wall
The success of a curtain wall system depends on two important features that are the quality of gaskets, and sealants and the quality of installation of the panels to the main frame. Therefore, curtain walls and sealants require regular maintenance to maximize their life. The typical life of any curtain wall generally is 10-15 years. The most common framing system is anodized aluminium which has to be cleaned from time to time to prevent corrosion of aluminium. Sometimes, it needs re-coating or re-anodizing also.
The Design Considerations
The material of the frame
Solar optical properties
Solar heat gain control
The type of installation
Regular maintenance system
The challenge for an effective, waterproof and long-lasting curtain wall system lies in designing and evolving the best strategy for sustainability of the same by employing good design practices to ensure an aesthetically pleasing façade apart from achieving durability, quality installation and good maintenance. Consequently, the curtain wall, not only serves a practical purpose but also advocates transparency, utilitarianism and flooding the interiors with light physically and altruistically at the same time. Flexibility in the fabrication and installation of the Curtain Wall with a dose of Creativity can transform a building’s façade into an impressive and iconic, landmark. Curtain walling thus helps architects, fabricators and installers to bring a creative answer for both new projects and refurbishments right to the doorstep of their clients. Moreover, not the least but connecting the soul of the building with the cosmos, the transparent glass becomes the interface between the connections.