In the field of contemporary architecture, curtain wall systems are used to transform buildings into eye-catching structures while helping achieve various efficiencies. These systems are usually made of glass or lightweight materials that just hang on the outside of a building like an envelope and serve various practical purposes in addition to creating beauty.
This architectural innovation originated in ancient times and has proven very effective in keeping buildings, especially those made of glass or non-structural exterior walls, safe from external attacks.
However, modern curtain wall systems offer more than just protection from attacks. They also improve thermal performance, noise control, daylighting, and privacy. Here is a detailed look at this architectural phenomenon.
If you have ever looked at buildings such as the Empire State Building, The Crystal Palace, and The Bank of China Tower, you've probably noticed that they have a non-structural fabrication, usually glass or lightweight material that just hangs on their exterior walls like a skin. The fabrication comprises a framing system (vertical and horizontal rails) that supports in-fills of glass or thin stone.
The framing itself is not load bearing but is attached to the building structure to transfer the system's gravity and wind loads to the building at the floor line. Different buildings use curtain walls for different reasons, including modulation of heat, light, wind, dust, and noise. They also absorb and distribute forces and pressure, preventing high-rise buildings from swaying in high wind scenarios.
If you are interested in these architectural phenomena, you'll be glad to learn that they are available in an assortment of styles and material combos, including glass and steel, glass and aluminum, glass and wood, plus textures such as brushed, smooth and matte and shapes such as oval, triangular and curved.
The point is that you can design a curtain wall system to match your building's style. Of course, most modern designs use aluminum in place of steel because its excellent machinability properties allow architects and engineers the carte blanche to develop designs that make their clients' buildings the talk of the town.
If you don't believe us, just check out the curtain wall system that adorns The Burj Khalifa, with thousands of prefabricated glass panels set within aluminum frames in a double-layer arrangement and accented with stainless steel fins shaped like the tips of an arrow. It's one of the most popular 22nd-century architectural marvels.
Of course, curtain walls aren’t a modern invention; even before the extrusion process was invented, folks experimented with glass and wood curtain walls. These were rather primitive systems and prone to a horde of problems, including water infiltration, wind loads, fire, and noise intrusion. Following the invention of the extrusion process, iron replaced wood as the framing material, but the systems still suffered from weight problems until aluminum extrusion became possible.
Aluminum has a high strength to weight ratio, allowing framing systems to remain sleek yet strong. Additionally, it’s now easier to address leakage, insulation, and noise infiltration issues thanks to technologies and techniques such as reflective glass, fiberglass, heat-tempered glass, PVC, rubber, resin sealants, etc.
Curtain wall systems comprise many different parts, but the framing, glazing, spandrel panels, and anchorage are the main ones.
The framing comprises the horizontal and vertical rails that support the panels. They are typically made of steel, aluminum, or composite materials. However, aluminum is the most popular choice because it's lightweight, highly malleable, and corrosion-resistant. The horizontal members are called transoms, while the vertical ones are called mullions. The most popular framing methods are stick-built and unitized.
The former involves assembling the mullions and transoms on-site and installing the opaque or glass panels. The latter involves complete individual panels with mullions, transoms, and glass already installed.
Expect to pay more for pre-fabricated systems than stick-built walls. However, prefabricated systems are easy to install and do not require much labor. That said, you won’t be able to put your ‘stamp’ on the design because the system arrives fully assembled. With stick-built designs, you can assemble the system one by one until you achieve the style you want.
Glazing refers to the panels that fill the space between transoms and mullions. These can be glass or opaque, depending on your privacy needs. They are important for functionality and aesthetic purposes. Different glazing options include single, double, and triple glazing. The former is the simplest because it only consists of one glass panel, while double glazing features two glass panels separated by an air space for improved heat and sound insulation.
Triple glazing consists of three panes of glass separated by two air spaces for even more energy efficiency and sound insulation. In any case, the glass type and thickness and the panels' size matter. Go for thicker and low-emissivity glasses for increased energy efficiency and noise reduction.
The other areas of curtain wall systems not occupied by glazing are filled with spandrel panels. These can be made of various materials, including glass, metal, stone, and concrete, and play functional and aesthetic roles such as adding color, texture, and pattern, concealing unsightly elements, improving energy efficiency, protecting against fire, and providing a visual transition between the windows and the surrounding walls.
Spandrel panels can also help achieve a visually striking facade by breaking up the monotony of rows of windows.
Just because curtain walls are a non-structural fabrication doesn't mean they don't need to be anchored. There are various ways to attach curtain walls to a building. Anchoring helps the system to support its own intrinsic weight and remain secure amidst seismic forces, wind load, thermal expansion and contraction, etc.
Anchorage options include F&T Clips, Dead Load and Wind Load Clips, F Perimeter and Embed Anchors:
●F&T Clips: T-clips anchor the curtain wall systems at the mullion, while F-clips do so at the jamb. They are easy to install and tape into place.
●Wind loading involves slotting the anchoring clips to allow movement but still makes them resistant to pressure and forces from the wind. On the other hand, dead loading uses bolts to set clips in place; movement is ensured via working splices.
●F perimeter anchors are aluminum extrusions used at the jambs to restrict deflection and reduce joint sizes.
●Embed anchors don't attach to parts of the glazing system but are set in place when the concrete is poured and help secure system clips.
Curtain wall systems can also come with features such as weatherproofing, sunshades, lighting systems, alarm systems, drainage systems, vents for air circulation, or flashing to seal joints and improve insulation.
At the very basic, building facades are used to stop water from seeping into buildings. Features of waterproof curtain wall systems include frames made with wept glazing and tilted pocket sills to direct any water that seeps through the glazing outside. Other features include perimeter sealants such as rainscreens, flashings, etc. These features also keep out air, preventing heat loss or gain depending on the prevailing external temperature conditions.
Even though curtain wall systems are non-structural add-ons, they still help against wind loading, thereby contributing to the overall stability of the buildings. They absorb any kinetic forces from high winds and disperse them throughout their structure and frames, thus eliminating any unwanted stress from the building. This stress-prevention property of curtain wall systems makes them very useful, especially in high-rise buildings. It prevents them from swaying due to high winds, thereby remaining comfortable for occupants.
In case of a building fire, a curtain wall system can help slow its spread between floors, reducing the work needed to put the flames out before they raze down the building. Depending on the system's materials, it can act as a barrier that keeps fires from jumping between floors.
This property is especially beneficial in high-rise buildings where fire would otherwise spread upwards quickly. Of course, do not forget to check the system's fire resistance rating. All curtain wall systems feature a fire-resistance rating, which simply is a measure of the duration of fires they can withstand before failing.
It all depends on the system material. Inspect the materials to see if they coincide with the system's assigned fire rating, and choose wisely.
Curtain wall systems can also contribute to a building's overall thermal efficiency, especially if glazed and treated properly. Curtain walls act as the skin of a building, minimizing heat loss in winter and temperature gains in the summer, thereby reducing the need for constant interior heating or cooling. Glazing also stops UV penetration, which would otherwise make items inside the building lose color and quality fast.
Curtain wall systems improve natural illumination inside buildings, enhancing the working environment and reducing the need for artificial lighting. This helps reduce eye strain, improve mood, and reduce monthly lighting bills. The system also makes the interior of a building appear bigger and more spacious, helping building owners optimize space usage.
Curtain walls can also help reduce noise, especially in buildings in urban setups prone to noise pollution. Curtain wall systems use glazing, infills, and internal seals to keep noise from getting through. Some designs also use thick double glass panels with a polyvinyl butyral interlayer to absorb vibrations and stop them from propagating through the structure.
The noise-reducing and natural lighting advantages of curtain walls are very useful for achieving an ambient working environment.
There's no denying that enveloping a building in glass or lightweight material helps make it aesthetically pleasing. You can experiment with different shapes, colors, textures, and patterns to achieve the look you want. Glass options include float, annealed, tempered, laminated, tinted, reflective, and insulated glazing units. On the other hand, aluminum options include painted, polished, and anodized products.
As already mentioned, some iconic buildings worldwide feature curtain wall systems. Be sure to check out the following buildings to see how they utilize curtain wall systems for practical and aesthetic purposes.
●London's Crystal Palace. The first architectural structure to feature a glass curtain wall
●The Empire State Building in NY, with its glass and steel curtain wall
●The Willis Tower in Chicago with a steel and glass curtain wall, too
●Dubai's Burj Khalifa with an aluminum and glass curtain wall
●The Petronas Twin Towers in Kuala Lumpur with aluminum and glass curtain wall
When designing and constructing curtain wall systems, engineers face various challenges, alright! Not only do they have to consider factors such as wind load, corrosion, water infiltration, debris impact, and thermal expansion and contraction, but also the environmental impact of the curtain walls.
Materials such as aluminum and glass are reverentially friendly. Both can be recycled at the end of the structure's lifespan, keeping them from landfills. Plus, aluminum is a naturally abundant resource that doesn't require huge amounts of energy to mine and process. Of course, curtain walls also improve natural lighting and energy efficiency, helping live a greener lifestyle.
Advancements in technology have also produced materials such as PVC rubber and shape memory alloys to help with some of the performance issues. Some curtain wall designs use PVC and rubber thermal breaks to improve insulation. Others use shape memory alloys designed to change shape according to the prevailing temperature and environmental conditions.
Additionally, an explosion in computer-aided design has made it possible to design and analyze curtain wall systems for weaknesses easily.
If you plan to add a curtain wall system to your building, work with a renowned manufacturer to select a curtain wall that suits your needs and budget and install it in a way that maximizes performance and cosmetic function. JMA is a sheet metal factory with decades of experience in aluminum extrusion and fabrication.
We produce about 600,000 tons of aluminum products annually, including doors, windows, and industrial materials. We also specialize in the study, development, fabrication, and supply of curtain walls. Whether you want a stick-built or unitized curtain wall system, we can help.
We also offer designs in thermal break and ordinary options to suit your project's requirements. Visit our products page for a good look at some of our products, and let us know what you need to achieve your curtain wall system project.
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