Curtain Wall Innovations

As efficiency demands rise, modern curtain walls are becoming critical in achieving project sustainability and long-term energy goals. When properly designed and installed, they can help mitigate air infiltration, enhance indoor thermal comfort and reduce operational energy demands.

Even with these benefits, some still ask are curtain walls environmentally friendly?

Based on how they are engineered and perform over time, steel-framed glass curtain walls offer distinct advantages that support environmental goals in ways traditional systems, such as aluminum curtain walls, may be unable to match.

How can steel curtain wall elements reduce air infiltration and energy consumption?

Controlling air leakage is one of the most impactful ways a curtain wall system can support environmental goals. Uncontrolled air infiltration allows conditioned indoor air to escape while drawing unconditioned outdoor air inside. This forces HVAC systems to work harder, increasing energy consumption and operational emissions.

Modern steel-framed curtain walls can be particularly effective at mitigating air infiltration, especially in cold or highly variable climates. These systems can incorporate advanced gasketing strategies. Gasketing on the face of the steel frame isolates the steel from air within the glazing channel, while carefully detailed perimeters and compatible infill panels, such as glass or metal panels, work together to create a highly effective air and water barrier. The result is a tighter envelope that supports consistent indoor temperatures and improved energy performance.

This in conjunction with steel's low coefficient of thermal conductivity, which is approximately 74 percent lower than aluminum’s, minimizes heat transfer to help HVAC systems maintain a comfortable indoor environment more efficiently.

Performance drives sustainability in steel-framed glass curtain wall

At the most basic level, the materials and glazing that comprises a curtain wall influence its ability to contribute to sustainability goals. That said, for both steel and aluminum curtail walls, performance-driven design often determines long-term environmental value.

When specified with robust, high-performance glazing, structurally efficient framing and well-detailed air and water barriers, steel-framed curtain walls can be an effective component of an environmentally responsible building envelope. In addition to supporting operational efficiencies, steel’s strength allows larger lites of high-performance glass with fewer and narrower sightlines. This can help projects achieve LEED credits for Daylighting and Quality Views.

Properly engineered and installed systems help buildings use less energy, improve occupant comfort and perform better throughout their service life. For this reason, it is important to evaluate these systems as components of a building as well as building performance as a whole when answering the question are curtain walls environmentally friendly.

Continuous gasketing with ultra-wide gasket faces helps modern steel curtain wall systems seal and protect buildings from air and water exposure. The extruded silicone gasketry covers the face of steel and completely isolates it from contact with water. When paired with precise perimeter detailing and compatible materials, this configuration also makes air infiltration nearly nonexistent. With such a highly durable barrier against air and water infiltration, leading prefabricated steel curtain wall systems contribute long-term performance and façade integrity.

Air Infiltration

A curtain wall minimizes air infiltration when the gaps between framing components are filled with a continuous, extruded silicone gasketing.

To quantify their ability to resist air infiltration, these systems are tested to ASTM E283/E283M, Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Skylights, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen.

Prefabricated steel-framed curtain walls, like Technical Glass Products’ (TGP) SteelBuilt Curtainwall® System, demonstrate air leakage rates of 0.01 cubic feet per minute per square foot (cfm/sq. ft.) or less at a pressure differential of 6.24 psf. This is partly due to their ultra-wide silicone gaskets and partly due to their single-source fabrication, which leads to a consistent fit and finish.

This single-source approach to prefabricated curtain walls mitigates air infiltration by maintaining consistent fitting across the co-extruded, perimeter silicone sheet flashing, steel framing, ultra-wide gasket faces, intersection compression plates and other components. Further, when these systems include sliding shear clips, they ease installation challenges without compromising air infiltration resistance.

Water Infiltration

The same continuous gasketing and perimeter silicone sheet flashing also protect against water infiltration by creating a sealed barrier between framing components.

The barrier these extruded and co-extruded silicone components create directs any water that contacts a prefabricated curtain wall towards the vertical mullions to be efficiently drained from the system. Enabling the glazing to resist water penetration at 15 pounds per square foot (psf) or higher, this engineered water management system meets ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors and Curtain Walls by Uniform Static Air Pressure Difference.

For added protection, installers seal the lapped gasket joints at horizontal-to-vertical connections, preventing water from reaching steel back members and interior occupied spaces.

As more projects look to reduce embodied and operational carbon, building professionals are increasingly holding each element of a building’s façade to higher scrutiny. This includes curtain walls.

While the design and installation of these systems is critical to achieving long-term sustainability goals, the materials that comprise them can be equally important. For most modern glass curtain walls, the options for framing are either aluminum or steel. When answering the question are curtain walls environmentally friendly, it is important to quantify the material capabilities of the systems to make the best decision for a project.

Embedded energy and recyclable content: steel and aluminum curtain wall compared

Although both steel and aluminum framing systems are fully recyclable, their embodied carbon profiles differ.

Primary steel production generates approximately 2,540 lbs of carbon dioxide equivalent per short ton of material, compared with roughly 7,530 lbs of carbon dioxide equivalent per short ton for primary aluminum. Steel framing typically contains 15 percent to 25 percent recycled content, while aluminum curtain wall framing profiles may include up to 30 percent recycled material. The limited global availability of scrap metal influences these percentages.

For SteelBuilt Curtainwall® Systems from Technical Glass Products (TGP), the frames contain around 25.8 percent recycled material, 21 percent is post-industrial and 4.8 percent is post consumer. This percentage puts it within LEED references for steel use and may support prerequisites for credits.

While recycled content is an important consideration, it should be evaluated alongside long-term performance to fully understand a curtain wall system’s environmental impact.

Steel frames support high-performance glazing better than aluminum curtain wall framing

One effective way curtain walls contribute to energy efficiency is by accommodating high-performance insulating glass units (IGUs).

In these scenarios, the structural capacity of aluminum curtain walls may limit design potential. The lightweight material has a lower modulus of elasticity, roughly one-third that of steel. So while aluminum is more flexible, it is more prone to sagging or bending under heavy loads. Supporting thicker, larger IGUs may require reduced glass lite sizes or free spans to manage deflection demands. This increases the amount of framing material, negatively impacting both aesthetics and performance.

Steel-framed curtain walls can accommodate glazing infills up to 3 inches thick and weights up to 23 pounds per square foot (lbs/sf). For comparison, a typical triple-glazed unit measures approximately 1.7 inches thick and weighs around 10 lbs/sf. This capability enables project teams to specify robust glazing systems that significantly improve thermal efficiency without compromising glazing area, transparency or design intent.

NFRC 100 computer simulations further underscore this performance potential. These models recorded U-values as low as 0.19 Btu/h·ft²·°F for steel framing systems with triple glazing, clear glass and non-gassed airspaces. While these values are approximate, they demonstrate how steel framing can support exceptional thermal performance.

Materiality plays a role but does not tell the complete story of sustainable curtain wall design

The answer to are curtain walls environmentally friendly involves evaluating a system’s materials. This is an important first step in determining how it will contribute to a project’s sustainability goals. However, it is not the only one.

In addition to material, project teams are encouraged to examine the design, context and suitability of a curtain wall to completely understand how these systems can support a more environmentally friendly approach to design.

Gone are the days where every building conformed to completely vertical lines. Today’s advanced steel curtain walls can accommodate these contemporary design sensibilities. They can be used to create angles, slopes and achieve great free spans, creating truly dramatic results.

A curved curtain wall aesthetic can be achieved by using steel mullions to create a segmented curtain wall system. Typically with standard steel systems the degree of turn is limited to a maximum of 10 to 12 degrees at any single mullion, while larger turning angles require variations on extruded aluminum cover caps or glazing adaptors and gaskets. With custom modern steel systems, design teams can have a greater degree of turn to achieve a tighter radius.

Design professionals wishing to achieve a seamless, “frame-free” look on the exterior side can use structural silicone glazed (SSG) steel curtain wall systems (see SteelBuilt Curtainwall® SSG System). These systems eliminate the need for pressure plates on either two sides or all four sides. They use silicone to support the “free” or uncaptured glass lite’s edges via other strategies, such as with a cassette / toggle system. The latter is a beneficial solution since most silicone manufacturers do not permit adhesion to carbon steel profiles for structural silicone applications. Steel SSG systems require a face gasket applied to the steel framing, which ensures a two-line air- and water-defense strategy. Notably, the gasket, if the structural silicone were applied directly between glass and steel profiles, would short-circuit that 2-line defense and allow water contact with the steel inside the glazing pocket, potentially leading to corrosion.

Fully- or partially captured systems, regardless of the number of sides encapsulated, have a snap-on cover to conceal pressure plate screws, creating a sleek, modern look, much like their aluminum counterparts.

Steel framing is also compatible with point-supported glazing systems. In these assemblies, steel mullions function as the structural component. The glass is supported by custom connectors (i.e. ‘spiders’), which in turn structurally attach to the steel supporting member. This helps ensure the structural component has a narrow sightline and a smooth, monolithic exterior.

Every year, curtain walls continue to soar higher, form angles that are more challenging and push the building envelope closer towards total transparency. Here’s a look at popular trends that are allowing architects to reimagine these design-forward systems.

More glass

Glass manufacturers, from float line to fabrication operations, are able to create larger lites (often referred to as “jumbo” lites), incorporating many of the features of the past. From thermal shading, Low-E and reflective coatings to heat treating and lamination, they can combine them into all aspects of insulating glass unit (IGU) production. Floor-to-ceiling glass sizes are now the bottom of the spectrum of the glass that can be accommodated in these steel systems, creating even greater soaring free spans of glass in today’s curtain wall and window assemblies. The benefits of these large expanses of glass are daylighting and clear views to the outdoors, which lend to helping architects achieve LEED requirements.

Curtain walls of the past were often only 13 feet tall, now it is not uncommon to see more than 14 feet or higher ceilings. Glass is also getting thicker to meet deflection limits and aid in its ability to meet higher wind loads for the increased area of individual lites. Some builders are even pushing the envelope through the strength of steel framing in curtain walls to use larger pieces of glass.

Less Framing

With the rise of new-generation steel curtain wall framing, a building can now handle approximately 40-foot free spans in a single member without splicing, additional internal reinforcement, or more frequent connections to the building structure. This helps provide uninhibited sightlines into and out of the building and requires less framing. Additionally, since steel framing is three times stronger than aluminum assemblies, its profile size can be nearly two-thirds that of a comparable aluminum profile while still meeting the same curtain wall performance criteria. This helps to shift viewers focus off the frames and onto the glass and what is behind it.

Complex Framing

Individual glass lites no longer need to be limited to rectangles. Because of the production efficiencies realized by modern fabrication methodologies, the use of trapezoidal, parallelogram, or triangular lites (or other “patterned” glass shapes) can be easily framed by steel systems.

Electrochromic Glass

Electrochromic glass is smart-technology glass that automatically tints in response to the outdoor climate and lighting conditions. This helps occupants inside the building enjoy a comfortable, well-lit interior. Electrochromic glass is becoming more popular as green requirements get more stringent. The glass can be used on curtain walls to create long-term savings that include the glass’ potential to cut back energy costs by blocking unwanted solar energy and / or glare. With this glass, occupants don’t need blinds or shades because the glass does the shading adjustment automatically for them.

Glass curtain walls have become a defining feature of modern architecture, used in everything from storefronts to multi-story facades and interior applications. Over the years, these glazing systems have featured larger expanses of glass and sleeker framing profiles than was previously possible. These expansive curtain walls with more glass and less frames are a pictorial representation of what the advantages of steel in curtain walls are today.

As a high-performing material, steel’s strength is capitalized through advanced material forming methodologies that make it possible to have narrower frames support larger loads. This has transformed the design and performance capabilities of glass curtain walls today. For example, SteelBuilt Curtainwall Infinity™ System by Technical Glass Products (TGP) leverages steel’s high modulus of elasticity (three times greater than aluminum) and can span up to 40 feet (ft) free spans in a single member without splicing. The glazing system can use any type of custom steel member as a back mullion almost, allowing architects and designers to use larger areas of glass, smaller frame profiles and greater free spans.

Because SteelBuilt Curtainwall Infinity frames are precision-engineered using laser cutting and welding techniques, they are narrower than comparable systems and have well-defined edges rather than rounded profiles. Additionally, some profiles can eliminate the need for visible weld beads or fasteners at the vertical-to-horizontal framing joints. With these properties, TGP’s steel curtain wall systems can maintain uninterrupted sightlines.

Furthermore, today’s steel profiles are highly resistant to corrosion, thanks to durable primers and protective color coatings. Fabricators can further enhance the durability of a curtain wall by incorporating moisture protection technologies, such as continuous gasketing, to prevent water from coming in direct contact with steel.

With these advancements, steel can not only improve the structural and thermal performance of glass curtain walls but also offer greater design flexibility. By leveraging the SteelBuilt Curtainwall family of frames, architects can marry aesthetics with high performance in a way that pushes the needle forward for modern architecture.

As architects evaluate façade strategies for commercial projects that aim for higher performance and sleeker aesthetics, one question often surfaces early in the design phase: Why do architects prefer curtain wall over window wall systems? The answer starts with understanding the distinctions between glass curtain walls and window wall systems, both of which play important roles in modern building envelopes.

A glass curtain wall is a non-load-bearing system, used on the building exteriors as well as interiors. On the façade, the glazing system is supported from the building’s structural frame, typically spanning multiple floors. Glass curtain wall delivers a continuous, visually uninterrupted surface. When paired with the strength and slenderness of steel framing, glass curtain walls can support larger expanses of glass with fewer intermediate members than comparable aluminum-framed system, enabling the lean profiles and seamless transparency many commercial buildings strive for today.

Additionally, glass curtain walls enable thermal efficiency. Because they span multiple floors continuously, curtain walls can incorporate uninterrupted thermal breaks or advanced gasketing systems along the framing. This continuity reduces thermal bridging, helping to maintain consistent interior temperatures and improving energy efficiency.

By contrast, window wall systems are generally installed slab-to-slab, with each unit sitting between floor plates. This creates a modular configuration that breaks at every level and naturally introduces horizontal sightlines. While this can simplify certain detailing and improve installation efficiency, the segmentation can also limit the openness and visual purity designers often seek in contemporary projects today.

Furthermore, it also introduces more horizontal and vertical joints, which can be points of thermal bridging as well as air and water leakage. As a result, even with high-quality glazing, window wall systems may not be able to match the thermal performance and airtightness of a well-designed curtain wall.

Ultimately, both curtain wall and window wall systems can bring generous daylight deep into building interiors and modern glass expression to a project. That said, curtain wall systems generally perform at higher levels for air, water and structural loading than that of most commercial window systems. For instance, Fireframes® Curtainwall Series might have more meaningful impacts on overall façade design than a fenestration of Fireframes Designer Series with monolithic glass, rated or non-rated. Understanding the strengths and limitations of each approach can help project teams select the glazing solution that best aligns with their building’s goals, scale and design intent.