Continuous facades: types, materials, and benefits of the construction system that has revolutionized the appearance of contemporary buildings
With its glass surface that appears to blend with the surrounding environment, the continuous facade has made it possible to achieve complete integration between the interior spaces of buildings and the surrounding landscape. To successfully design an attractive continuous facade that ensures the comfort and safety of occupants, various aspects, including architectural, structural, and energy-related, need to be balanced and assessed. Therefore, in the design phase, adopting the BIM methodology and using building design software to model the building in 3D, evaluate the aesthetic impact of this construction system, and perform accurate structural and energy analyses can be of great support.
Let’s find out more in this article!
What is a Continuous Facade?
The continuous facade, or “curtain wall” in English, is a vertical enclosure that resembles an uninterrupted curtain made of lightweight materials (such as glass) and performs the typical functions of an external wall. This structure has no load-bearing function; it supports no weight other than its own and must only deal with horizontal forces, such as wind. The load-bearing function is entirely entrusted to the structure, usually consisting of steel or reinforced concrete columns and beams.
The continuous facade is known for its versatility, as it can be constructed with both transparent and opaque panels, combining all the features of a traditional building enclosure with distinctive design. Additionally, it can be designed to be fire-resistant and capable of withstanding projectiles, often by using bullet-resistant glass.
Its appreciation began with the global spread of rationalism and Le Corbusier’s five points of architecture, becoming increasingly symbolic of architectural evolution and the affirmation of modernist design and aesthetics.
Today, “curtain walls” are commonly made with extruded aluminum structures. However, some applications involve the use of steel structures due to their physical and mechanical properties, allowing for wider spans and manageable thermal expansion.
These metal structures, consisting of vertical mullions and horizontal transoms, are typically glazed with high-performance glass, promoting the entry of natural light and environmental control.
In practice, these glass continuous facades have redefined the relationship between the interior and exterior spaces of buildings, allowing for greater integration with the surrounding environment.
The main types of continuous facades vary depending on the method of attaching the cladding panels to the framework. These include:
- Mullion and Transom Facades: This is the most common type of continuous facade and consists of horizontal and vertical components that remain visible. The enclosure is assembled in parts and includes:
- Vertical mullions attached to the building’s supporting structure;
- Horizontal transoms anchored to the vertical mullions;
- Opaque or transparent panels (non-openable);
- Openable elements also attached to the mullions and transoms;
- Structural Glazed Facades: The distinctive feature of this system is the planarity of the glazed surfaces, which conceals the load-bearing metal structures. The surface continuity is interrupted only by the joints between the glass panes, barely noticeable from the outside. The system consists of glazed elements, both openable and fixed, with the glass connected to the underlying framework through structural adhesives (structural silicone) that transmit all loads to the framework itself. Some systems also use mechanical elements (not visible from the outside) in addition to the adhesive silicones to secure the glass panels;
- Modular Facades: This system is constructed using components similar to mullion and transom systems, but unlike the latter, it is assembled as a set in which basic elements are prefabricated into modules (or cells) in a factory, transported to the construction site complete with opaque and transparent panels, and then installed. This system is particularly useful for construction sites where the erection of external scaffolding is unfeasible or uneconomical, such as in tall tower buildings. The assembly of modules in the factory provides greater quality assurances but, compared to a mullion and transom system, requires more physical storage space and specific transport methods. The system is also known as “Precast”;
- Double-Skin Facades: Comprising an enclosure with two parallel transparent walls, creating an air gap in between. This solution allows for better thermal transmittance and acoustic insulation than single-skin continuous facades. Within the air gap, the heating of the air due to the greenhouse effect generates airflows that are directed outward or inward into the building (chimney effect). The accumulated heat can be used for heating the building in cold seasons or expelled in the summer to control overheating. To control summer overheating, the system is equipped with sunshades placed within the gap between the two “skins”;
- Point-Supported Facades: This type can be divided into two subsystems:
- Independent panes (VEA, vitrages extérieurs attachés, or suspended curtain walls). The system consists of transparent panes supported by mechanical anchoring devices that fix them near the corners. These devices, typically made of metal pins, transfer the weight of the glass to a distant underlying structure away from the transparent surface. The supporting structure can be made of metal alloys or other materials (there are systems that use mullions made of glass plates positioned perpendicular to the facade). The category of point-supported facades also includes suspended facades, where the panes are anchored near the corners (similar to the previous system) and interconnected without a rigid supporting structure. In this system, the own weight of each glass element is transferred to the one immediately above it until reaching the upper structural elements (the building’s supporting structure). The transparent surface becomes self-supporting, while horizontal forces (dynamic wind forces) are controlled by internal bracing systems (typically) placed inside the facade and consisting of a set of “tensioned” cables.
The Evolution of Continuous Facade
During the 19th century, a widespread adoption of metal and glass structures was observed, including structures such as railway stations and greenhouses. This trend was facilitated by a series of factors, including the abolition of the glass tax, the importation of tropical plants that required suitable cultivation spaces, the advancement of construction science allowing precise material behavior analysis and sizing, and industrial developments.
One of the iconic examples of this trend is the ‘Palm House’ at the Royal Botanic Garden in Kew, London, built between 1845 and 1848 by Richard Turner and Decimus Burton, and the Crystal Palace, a massive Victorian-style glass construction erected in London in 1851 to host the first World Expo.
However, the real turning point in the evolution of the continuous facade came with the contribution of the Chicago School in the late 19th century. Architects such as William Le Baron Jenney, Louis Sullivan, and the Holabird & Roche studio played crucial roles. The ‘Tacoma Building’ of 1884 was the first building where the continuous facade was applied to the structural framework of the building itself, introducing the concept of the ‘spandrel,’ an opaque panel that covers the view of structural elements, typically positioned at the floor level and harmonized with transparent panels to maintain facade continuity.
Le Corbusier continued to develop and refine the concept of the continuous facade in his works, using it as an architectural element to create modern, functional, and aesthetically advanced spaces. His idea was to create ‘rationalist’ architecture that addressed the needs of modern life and efficiency, with a clear separation between the building’s structural framework and the facade, made possible by the adoption of reinforced concrete structures.
In the 1940s and 1950s, due to high material demand, manufacturers of metal components and fixtures began experimenting with new systems, such as bronze and aluminum. The 1960s and 1970s witnessed the development of structural silicone as a connection system between cladding components and the frame, enabling the creation of fully glazed facades with no visible profiles. A notable example of this evolution is the ‘860-880 Lake Shore Drive Apartments’ in Chicago, designed by Ludwig Mies van de Rohe between 1948 and 1951.
Starting in the 1990s, the continuous facade took on a role beyond mere enclosure, becoming a kind of ‘filter’ between the interior and exterior environment. Advanced solutions were developed, including double facades, those suitable for heat recovery, and photovoltaic facades. Furthermore, facades became a significant medium for visual communication, used in the so-called ‘media buildings.’
In conclusion, the continuous facade has undergone a significant evolutionary path over the decades, transitioning from a functional architectural element to an innovative and sustainable design expression that plays a key role in creating modern and cutting-edge buildings.
Construction of a Continuous Facade
The construction of a continuous facade requires carefully planned design and engineering. Here are the key construction details:
- Glass: Glass is the most common material for a continuous facade. Tempered or laminated glass is often used for safety and durability.
- Metal structures: Often made of extruded aluminum for its lightweight and strength. Steel may also be used for specific applications.
- Structural adhesives: Structural silicone or other adhesives are used to connect the glass to the frame, transmitting loads to the structure.
- Co-planarity: Design must ensure that all glass surfaces are co-planar, creating a uniform exterior surface.
- Insulation: Adequate thermal and acoustic insulation is essential for occupant comfort.
- Strength: Continuous facades must be designed to withstand wind forces, thermal fluctuations, and, in some cases, even fire or projectiles.
- On-site assembly: Continuous facade units are assembled on-site, often lifted vertically and attached to the building’s frame.
- Sealing: Accurate sealing of joints between glass panels is essential to prevent water infiltration and thermal leakage.
Purpose of a Continuous Facade
A continuous facade serves several crucial functions:
- Insulation: It provides thermal and acoustic insulation for the building, contributing to maintaining a comfortable indoor environment and reducing energy consumption.
- Protection: It shields the building from weather elements like rain, wind, and snow, keeping interiors comfortable and secure.
- Aesthetics: The continuous facade adds a modern and elegant aesthetic touch to the building, strongly defining its visual identity.
- Lighting: It maximizes the entry of natural light into interior spaces, reducing the need for artificial lighting and enhancing visual comfort.
- Sustainability: Continuous facades can be designed to improve the energy efficiency of the building, reducing environmental impact.
Benefits of Continuous Facades
The continuous facade can be highly advantageous for various reasons:
- Aesthetic Appeal: Continuous facades allow for innovative and eye-catching designs. They often serve as a canvas for architects to showcase their creativity. The seamless, uninterrupted appearance provides a modern and attractive aesthetic.
- Natural Light: The extensive use of glass in continuous facades promotes natural light penetration, reducing the need for artificial lighting during the day. This not only enhances the indoor environment but also contributes to energy savings.
- Energy Efficiency: When designed with energy efficiency in mind, continuous facades can contribute to better insulation, reducing heating and cooling costs. Double-skin facades, for instance, can improve thermal performance significantly.
- Environmental Integration: Continuous facades facilitate a strong connection between the building’s interior and its surroundings. This integration with nature can enhance the overall occupant experience.
- Customization: These facades offer a wide range of options for customization, including glass types, colors, and configurations, allowing architects and designers to tailor the appearance to meet specific project requirements.
In conclusion, continuous facades represent an innovative and functional architectural solution that has transformed the face of modern construction. With careful design and the use of appropriate materials, these facades offer a range of aesthetic, functional, and ecological advantages that make them a winning choice for many contemporary construction projects.
Creating a Continuous Facade with BIM Software
As we have seen, designing a continuous facade requires evaluating a series of fundamental parameters for the successful execution of the project. Let’s explore how, with the BIM methodology, you can manage all these aspects in a virtuous manner.
First and foremost, you need to start with the 3D modeling of the building. Using specialized BIM software for building design, you model the continuous facade in 3D using the appropriate BIM parametric object. In practice, you outline the building’s perimeter and select the type of continuous facade that meets your project requirements. You have a rich library with numerous models at your disposal, which you can also customize to suit your design needs. Furthermore, you work with parametric BIM objects to which you can associate data and technical information that can be useful at every stage of the building’s lifecycle.
For example, you can attach product technical data sheets, price lists for quantity surveying, maintenance notes, special specifications for achieving the work according to the rules of the art, and more. These pieces of information can also be updated over time and used during the maintenance and demolition phases of the building.
Another crucial aspect of BIM modeling for a continuous facade is the ability to visualize its aesthetic impact before actual construction. With renders, virtual tours, and real-time videos, you can navigate through the model as if it were real and analyze it in all its details to choose the most compelling design solution.
Finally, the 3D model can be used for other critical assessments, such as structural calculations, thanks to structural engineering analysis software, and energy assessments, using dynamic energy analysis and simulation software.