One component of high-rise building facades is the curtain wall system, which includes window walls, cladding elements, and the curtain wall itself, all of which make up the building’s exterior envelope. The importance of different types of curtain wall systems in the building’s structure is now comparable to that of other structural elements. Due to its increased exposure to the external environment, proper design, installation, and maintenance are necessary to ensure its functionality and sustainability.
Curtain Walls in Buildings
In contemporary architecture, curtain walls are essential components, especially for high-rise buildings, functioning as the building’s cladding to enclose and protect the interior spaces from external factors like wind, rain, and temperature changes. Apart from providing necessary insulation and weatherproofing, curtain walls also offer aesthetic advantages, enabling architects to design visually appealing facades that reflect the building’s purpose and style.
Now let’s take a deeper look into the functions of all types of curtain wall systems.
Prevention of Water Penetration
Preventing water penetration is a primary function of a facade, and achieving a completely impermeable sealed curtain panel system is not always feasible. Therefore, two stages of prevention are employed. The first level aims to provide complete water defense, and if that fails, a secondary level is implemented to facilitate the drainage of percolated water.
Air Impermeability
The function of air impermeability is primarily an environmental concern aimed at reducing the emission of carbon dioxide resulting from the rate of heat loss or gain between the external and internal environments.
The Ability to Withstand Wind, Thermal, and Acoustic Forces
Building cladding systems transfer wind forces to the floors, acting as linear supports. Large panel curtain cladding systems are typically one-way spanning, with each floor level supporting one level of wind load. A crucial function of facades is thermal insulation to reduce energy consumption and CO2 emissions. Both opaque and transparent areas of the facade require insulated materials. In addition, acoustic insulation is necessary for buildings located in city centers to isolate the interior from external noise. Massive structural elements such as masonry or concrete structures provide higher levels of acoustic insulation.
Solar Level Control
To reduce solar levels, a selective solar control coating can be applied to one glass surface, allowing certain wavelengths of solar radiation to pass through. This coating is termed “selective” because visible wavelengths of light can pass through more easily than infrared wavelengths. Ultraviolet radiation can cause degradation in certain spaces, such as an exhibition or material display areas. To prevent this, a UV-inhibiting film can be applied to the surface of the glazing glass.
Primary Types of Curtain Wall Systems
The types of curtain wall systems include:
- Stick or framed systems
- Unitized system
- Ladder system
- Rainscreen principle
Stick Curtain Walls
This type of curtain wall system involves assembling components piece by piece onto the building’s structure. It is typically employed for low-rise buildings or in smaller areas, as accessing higher elevations requires exterior access. The system offers flexibility, allowing for on-site adjustments. Although it offers the benefit of low shipping costs, the associated labor and time consumption should not be underestimated, as they tend to be quite high.
Unitized Curtain Wall Systems
The unitized curtain wall system requires pre-assembling the components in the factory and delivering them as a single unit to the site for installation, which removes the need for individual installation. Moreover, the size of the unitized curtain walls is in direct proportion to the building’s floor-to-floor height.
They are particularly popular in high-rise buildings, as they do not require external support such as cranes or scaffolding, only mini-cranes or temporary hoists. This system provides the benefits of rapid construction and good quality, as the components are produced in a factory environment. However, the shipping costs for this type of curtain wall system tend to be higher due to the need for larger and better protection during transportation to the site.
Ladder Curtain Cladding
The ladder curtain wall system is similar to the stick curtain wall system in that it can be constructed offsite and then transported to the building site. The ladder system is constructed in a manner similar to an aluminum ladder, with its components attached to the building’s structure. Once the ladder curtain wall system is securely connected to the building, glazing, and glass can be installed.
Components of Different Types of Curtain Walls
The complete curtain wall unit consists of the following elements:
- Transom
- Mullions
- Vision Glass
- Anchor
Transom:
A transom is a horizontal component that separates the glazing panels of a multi-story curtain wall system, forming a grid-like pattern and offering structural reinforcement. Typically composed of sturdy materials such as metal, transoms attach to the vertical mullions supporting the curtain wall system and vary in size and spacing depending on engineering and design specifications. These horizontal members also facilitate drainage and ventilation within the curtain wall system through features like weep holes or vents.
Mullions:
Vertical elements known as mullions connect and sustain the glazing panels or “lights” of a curtain wall system. Usually composed of durable materials like metal, mullions offer structural reinforcement for the entire wall.
Mullions can have varying dimensions and intervals, depending on the engineering and design specifications of the wall. Additionally, they may have different cross-sectional shapes, like rectangular or I-shaped, and can be either solid or hollow, depending on the desired performance and appearance of the curtain wall system.
Apart from offering structural reinforcement, mullions may also integrate drainage channels or thermal breaks to enhance the functionality of the curtain wall system. Additionally, they may have links to other building elements, such as floors, roofs, or walls, to ensure a sturdy and stable overall structure.
Vision Glass
Vision glass is a crucial element of curtain wall systems, as it consists of transparent or translucent glazing panels that enable occupants to have an unobstructed view of the outdoor environment and allow natural light to enter the building.
The materials used to create vision glass in curtain wall systems can vary and may include tempered or laminated glass, insulated glass units (IGUs), or polycarbonate. The choice of materials for vision glass is based on factors such as the building’s desired performance, thermal and acoustic insulation, and safety requirements.
Depending on the design and engineering requirements of the building, the positioning of vision glass panels in a curtain wall system may differ. For instance, vision glass can be stationary, or it can be designed to provide ventilation. The size and shape of the vision glass panels can also be modified to suit the intended aesthetic and performance of the curtain wall system.
Anchors in Different Types of Curtain Walls
Anchors in curtain walls are crucial components that connect the curtain wall system to the building’s framing or structure. These components are essential for transferring the weight of the curtain wall system to the building’s foundation and for withstanding wind loads and other external forces.
The type of anchor employed in a curtain wall system is contingent on the building’s design and engineering specifications. In certain curtain wall systems, anchors may be hidden within the mullions or other structural components of the wall, while in others, they may be visible from the exterior.
Depending on the building’s construction materials, such as concrete, steel, or wood, the type of anchor employed in a curtain wall system may vary. Examples of typical anchors include plate, channel, and rod anchors, each with its own benefits and drawbacks.
The choice of anchor for a curtain wall system is influenced by several factors, including the building’s location, the intended performance of the wall, and the building’s architectural style.
Let’s Take a Look at More Details
Panel Framing Details:
The split mullions and panel perimeters with visible transforms can distinguish a Unitized Curtain Wall system. On the other hand, a Sticky Curtain Wall system is a single unit with no splits. For longer spans, an intermediate transom may be necessary to split the entire vertical panel into two. Mullions and transoms are thermally broken to prevent condensation and avoid cold bridging.
Weather Tightness of Curtain Claddings
The issue of water permeability is a major concern when it comes to weather tightness. To prevent water from seeping in, impermeable insulating units, also known as glazed units, are used. Moreover, a gasket is provided to create a rebate. If any water manages to enter the gasket, it is directed towards the rebate and then drained out through the transom joints or mullion ends.
Support Conditions
Different types of curtain wall systems are suspended from the top and laterally supported at different floor levels. The majority of these supports are anchored at the edge beams.
Therefore, having a highly rigid edge beam is crucial to minimize larger deflections that could disrupt the entire curtain wall system. Proper edge beam design is especially important for highly glazed systems to prevent curtain wall damage and cladding damage. Alternatively, steel strong backs can be utilized to span between perimeter columns, eliminating the need to connect to edge beams or floor slabs. These strong backs typically consist of hot-rolled sections.
Structural Behavior of Different Types of Curtain Walls
Previous studies have indicated that different types of curtain walls can withstand lateral forces, such as earthquakes to some extent, but damage can still occur. While the damage can be repaired, it results in economic losses and business activity delays.
Curtain walls are considered to be structural elements of a building because they act as a barrier between the building’s exterior and interior environments and play a role in transmitting loads for structural stability. They transfer wind loads to the primary structure, resist seismic forces to keep occupants comfortable and support gravity loads.
In terms of building durability, curtain walls are effective at adapting to different temperature ranges, which is particularly important in high-rise buildings where temperatures can become elevated with increasing floor numbers, posing a risk to occupants. Curtain walls must also be resistant to water penetration to prevent corrosion.
What Type of Curtain Wall is The Best For Your Project?
Choosing the best curtain wall system for your project depends on various factors, including the building’s height, location, and orientation, as well as your design requirements, budget, and schedule. It is recommended to consult with a professional architect or a curtain wall contractor to help determine which system would be the most suitable for your specific project. They can assess your project’s unique needs and constraints and provide you with options and recommendations based on their expertise and experience. Additionally, reviewing case studies and examples of similar projects can better understand the strengths and weaknesses of different curtain wall systems and help inform your decision-making process.
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