Want a Breathtaking Building Façade? Compare These Curtain Wall System Options First

A building's facade, or exterior face, is often the first impression it makes. For modern commercial and institutional buildings, curtain wall systems have become a popular choice to create truly breathtaking facades that stun and inspire. But with so many design options, how do you choose the right curtain wall system for your project's visual impact, performance, and cost goals?

First, we'll define curtain wall systems and the role they play in facade design. Then we'll overview the main factors to consider when evaluating different system types. Finally, we'll do a deep dive comparison of the most common options--stick, unitized, and panelized--along with examples and pros and cons of each. Read on for the complete guide to picking the perfect curtain wall system for your next showstopper building.

Key Factors to Consider

While aesthetics are paramount, several technical factors come into play when specifying a curtain wall system. Keep these key considerations in mind as we examine the leading options:

Height and Accessibility

The building's height and accessibility constraints will impact whether an onsite or offsite fabricated system makes the most sense. For lower rise buildings, stick systems assembled piece-by-piece onsite are usually perfectly adequate. But for high-rises, unitized or panelized systems prefabricated offsite become more practical.

Structural Requirements

All curtain walls must withstand wind loads and accommodate movement from seismic and thermal activity. Point-fixed systems offer greater versatility for complex structures. Unitized assemblies can also achieve excellent strength through robust corner assembly designs.

Thermal Performance

Energy efficiency has become a foremost concern in facade engineering. Maximizing R-values through insulated spandrels, thermally broken frames, and low-E coated glazing enhances thermal performance. Advanced systems like double-skin facades take this even further.

Aesthetic Design

The opportunities for all-glass facades, colorful spandrels, and custom shapes are virtually endless. Frame sightlines, vertical mullion spacing, and horizontal vision glass spans all affect aesthetics. The glazing percentage, shadow boxes, curved elements, and more offer creative freedom.

Cost and Installation Factors

Budget will naturally dictate options. Unitized systems involve higher initial fabrication costs but faster onsite installation. Operating and maintenance costs also require consideration for replacements, equipment access, and cleaning.

Stick Systems

Stick systems get their name from the process of assembling curtain wall components stick-by-stick onsite. The key parts include:

• Vertical mullions spans floor-to-floor to provide structural support
• Horizontal transoms form the floors spandrels
• Vision glass or opaque panels set into the grid
• Silicone sealant creates weather-tight joints

Erecting the sticks one piece at a time allows for immense design flexibility. Stick systems adapt well to curved geometries and complex angles. On the downside, piecemeal installation is slower and more vulnerable to quality control issues versus prefabrication. These factors make stick systems better suited to lower-rise applications.

Notable projects featuring stick curtain walls include the Sydney Opera House, Milwaukee Art Museum, and Manchester Civil Justice Centre.

Unitized Systems

Unitized curtain wall systems take fabrication to a more sophisticated level. Entire assemblies are prefabricated offsite in a factory as discrete units. These units, typically 5 to 10 feet wide, are then trucked to the site and craned into place like giant glass Lego blocks.

Unitized systems provide the major advantage of faster curtain wall installation compared to stick systems. Quality control is also enhanced in the factory setting. For tall buildings, the unitized process is vastly more efficient. Offsite prefabrication does involve higher initial costs. The modules also pose some limitations in achieving complex curvature.

Famous buildings with unitized curtain walls include One World Trade Center, Shanghai Tower, and 30 St Mary Axe (the Gherkin) in London.

Panelized Systems

Panelized curtain wall systems offer a hybrid approach. They use factory-built panels for rapid installation but are assembled into stick-like grids onsite. Panels may consist of various infills like:

• Glass vision panels
• Aluminum composite spandrels
• GFRC or metal panels
• Stone veneer rainscreen systems

Attaching panels to structural members onsite avoids the size and transportation cost constraints of fully unitized modules. This allows panelized systems to offer the versatility of stick systems with improved performance. The main drawback is a longer installation timeline than purely unitized construction.

The New York Times Building and the San Francisco Federal Building rely on panelized curtain walls to realize their aesthetics and functionality.

Other Notable System Types

Beyond the big three covered above, other curtain wall assembly methods fall into more niche applications. These include:

• Semi-unitized: Upper floors unitized, lower floors stick-built
• Point-supported: Glass attached at discrete points
• Ladder: Horizontal rails with glazed vision glass
• Cable: Glass suspended from cable trusses

Specialized systems like structural sealant glazing, tension structures, frameless glass walls, and double skins also serve unique design visions.

Key Takeaways

When approaching a new curtain wall project, establishing the visual design goals, building parameters, and budget constraints are paramount. With those defined, engineers can narrow down suitable system types and assemblies.

Stick systems offer ultimate flexibility for lower rises. Unitized systems streamline construction of high-rises. Panelized assemblies bridge the gap with a modular-stick hybrid approach. Beyond these frontrunners, variations on assembly principles and material choices are endless.

The optimal curtain wall strikes the ideal balance between aesthetic design, energy efficiency, structural integrity, constructability, and cost. It's a complex engineering puzzle but immensely rewarding when all the pieces come together in a gleaming facade that makes a bold architectural statement.

Curtain wall systems have opened up a world of possibilities in building design. Stick, unitized, and panelized constructions all bring unique advantages. Hybrid assemblies combine methodologies for specialized applications.

Ultimately, selecting the right curtain wall system relies on aligning needs to performance. With so many choices available today, almost any architectural vision can become breathtaking reality. Understanding these leading options lays the foundation for facade engineering success.