Photo courtesy Technical Glass Products (TGP)
As building envelopes grow more visually and functionally complex, glazed curtain wall designs have evolved to meet diverse and demanding requirements. No longer just a means of holding glass in place, today’s glass curtain walls are sophisticated systems that integrate advanced framing technologies, exterior cladding strategies, and protective finishes to meet diverse aesthetic, energy efficiency, and code requirements.
To meet these goals, architects are revisiting the fundamentals with fresh eyes. This includes exploring the possibilities of different framing system types, evaluating material pairings, and refining the details that support complex cladding strategies. The innovations transforming exterior clad curtain wall systems are not just about what is visible on the surface—they begin with the frame.
All in the frame
Steel and aluminum are the most specified materials for curtain wall framing systems. While steel is stronger than aluminum and can support larger free spans of glazing, corrosion issues have long plagued the hardworking material. In the wake of these concerns, aluminum rose to prominence with its lightweight, corrosion-resistant, and adaptable form. Today, advances in steel manufacturing are changing the landscape.
No longer prone to rust, steel profile systems can be made to be highly corrosion-resistant, protecting against dynamic and static water penetration, thanks to a continuous gasket that prevents water in the glazing cavity from coming into direct contact with the steel back members. Utilizing cold-roll forming and laser cutting/welding techniques developed in Europe, the profiles can be fabricated in longer spans and more complex shapes than ever. The possibility of spanning longer distances with fewer intermediate supports makes steel frames an excellent choice for expansive, high-performance facades.
Architects and facade engineers are also exploring innovative framing materials beyond traditional metals. These include mass timber curtain walls and glulam systems, as well as composite materials like fiber-reinforced plastics and carbon fiber, which offer exciting aesthetics and weight reduction opportunities.
Ultimately, the fundamental role of a glazed curtain wall’s framing system is to support and safely transfer all loads acting on the assembly. These loads include the weight of the glass infill, exterior cladding materials, framing components, and lateral pressures such as wind loads. In addition, the framing system must accommodate dynamic structural movements caused by live load deflection, thermal expansion and contraction, seismic activity, and any column foreshortening. It is necessary to account for vertical loads from snow accumulation in colder regions.
Ensuring structural integrity means a glazed curtain wall’s framing system must effectively transfer these loads to the building’s main structure through properly engineered connections. Beyond structural performance, curtain wall framing systems must meet applicable building codes and industry standards. In some regions, these codes can define deflection limits, movement tolerances, and seismic performance requirements, all critical factors in the design and specification process. Together, these factors make the choice of framing material extremely crucial to the performance and aesthetics of the facade.
Framing, cladding, and the details in between
As facade design gets more elaborate, architects are integrating a broader range of exterior detailing over glazed curtain wall systems. These can be purely decorative, highly performative, or both, contributing to the building’s visual identity. Materials such as metal, terracotta, glass fiber reinforced concrete (GFRC), fiber cement, high-pressure laminate (HPL), and even natural stone can be used to create decorative cladding elements that partially shield or entirely obscure portions of the glass curtain wall in a facade. These can be installed as rainscreen assemblies, patterned overlays, or sculptural attachments to give depth and variation to building design.
For example, perforated windscreens can help reduce wind pressure and harsh sun glare while adding dimensionality to the design. Similarly, to mitigate solar heat gain, metal sunshades and vertical louvers can be strategically placed over glazed surfaces that receive intense solar exposure, such as south—or west-facing elevations. Such design interventions help balance thermal performance and contribute to the facade’s rhythm and texture.
Manufacturers offer standard aluminum extrusions, or pressure plates, to secure glass infills within the frames using compressing gaskets. Typically, this helps create an air- and water-tight curtain wall. For added visual depth, designers may place decorative caps over these pressure plates. These larger caps can help achieve bold shadow lines or more sculptural effects. However, as layering additional cladding or large decorative elements over a glazing system becomes more ambitious, the detailing between cladding and curtain wall becomes a key design and engineering challenge.
Structural considerations for exterior cladding
When oversized decorative caps or layered elements exceed the structural limits of the cladding extrusions, careful evaluation is needed to determine how their added mass and loads are transferred back to the building’s structural system, usually through the glazed curtain wall or windows. Without this, the structural stability and performance of the wall system can be compromised. Horizontal elements must also be detailed to manage snow and ice buildup in colder climates, while vertical loads, uplift, and moment forces from the cladding must be addressed.
Cladding extrusions can be integrated over a steel-framed glass curtain wall or any framing system. Steel’s excellent strength, with a Young’s modulus Ε of approximately 207 million kPa (29 million psi), as compared to aluminum’s 69 million kPa (10 million psi), allows it to carry heavier cladding loads without requiring oversized profiles or more frequent supporting members. Mechanical reinforcement, such as supplementary anchoring, may be necessary to ensure secure cladding attachment, especially in areas subject to high wind pressure.
When the decorative caps’ size and weight exceed the retaining pressure plate’s load-bearing capacity, more robust strategies may be required to ensure a structurally stable facade. One way is to specify through-wall anchors positioned at the glass joints to tie the decorative cladding back through the glazing system to the structural frame. These anchors help ensure the layered system works in tandem with the underlying curtain wall framing, distributing loads safely and preserving the long-term integrity of the entire facade.
Managing dissimilar metals in facade design
For the cladding extrusions themselves, aluminum remains the standard due to its lightweight properties. Yet, designers may enhance the facade with thin-gauge sheet metals over glass curtain walls for added visual character or durability. For example, stainless steel offers excellent strength and finish variety, from polished to brushed to patterned, allowing it to complement a wide range of architectural styles. Brass, though less common, introduces a warm, golden hue but comes with higher costs and greater density. Copper and zinc add visual interest through their natural patinas and weathering behavior, which can be desirable in expressive facade designs.
However, using multiple metals in one elevation risks galvanic corrosion. This electrochemical process occurs when dissimilar metals come into contact with an electrolyte, such as condensation or rainwater, and can degrade one of the metals over time. Although steel-framed curtain walls are engineered to limit moisture intrusion with continuous gasketing, no system is completely impervious, making corrosion control a key consideration in detailing.
Although specifying a single metal type throughout a project would simplify corrosion control, this is often impractical due to factors such as material availability and the varying performance requirements of different building components. When combining metals is unavoidable, designers can reduce the risk of galvanic corrosion by selecting materials close to each other on the galvanic series. For example, hot-dip galvanizing the steel can reduce the electrical potential between the metals when connecting aluminum-framed curtain walls to structural steel.
If aligning materials on the galvanic scale is not feasible, corrosion can still be mitigated by electrically isolating the metals. This can be done by inserting non-conductive spacer materials with low moisture absorption properties, such as neoprene, nylon, plastic, or rubber. Also, corrosion-inhibiting pastes, sealants, or dried adhesives can be effective barriers. When choosing spacer materials, it is crucial to consider their design life and thermal expansion properties to ensure they are compatible with the primary metals and do not compromise long-term system performance.
Specifying finishes for the facade
Beyond the structural and material detailing, finish selection plays a critical role in the aesthetics and durability of the clad elevation. Anodized aluminum provides a durable, color-stable finish, while painted finishes, including liquid and powder coatings, broaden the range of color options available for aluminum and steel framing systems while adding protective layers.
Decorative metal finishes for thin-gauge materials range from polished and bead-blasted to brushed, rolled, or patterned textures and formed or brake-formed profiles, each contributing distinct visual and tactile qualities.
The case for integrated design thinking
In facade systems that incorporate cladding over glass curtain walls, the successful integration of framing, material selection, and finish detailing depends on early and sustained coordination across disciplines. Architects, structural engineers, glazing system manufacturers, and exterior wall consultants are critical in aligning structural requirements with aesthetic goals and constructability.
By proactively addressing challenges such as galvanic corrosion, load transfer, and long-term material compatibility during design development, design teams working with metal facades can mitigate costly redesigns and ensure that the envelope performs as intended.
Chuck Knickerbocker is the curtain wall manager for Technical Glass Products (TGP), a supplier of fire-rated glass and framing systems and specialty architectural glazing products. With more than 44 years of curtain wall experience, he has successfully worked with numerous architects, building owners, and subcontractors from the development of schematic design through installation.