Today’s designers have many façade options available to increase daylighting in commercial buildings. In the past, it was easier for designers to select a system based on its application. Curtainwalls, for example, were used for multistory buildings, while storefronts were used for one- or two-story buildings. Just as buildings have advanced in their designs and applications, fenestration systems have also advanced to meet market demands. Manufacturers now have expanded options across their product portfolios, which can make it difficult to determine the type of system that should be specified in certain locations. There are many differences within curtainwall systems that form a complex matrix of options.
Determine the level of performance
Curtainwalls provide a wide range of performance options. Standard curtainwalls provide an economical way of creating large spans of glass walls to clad the building envelope. They can typically meet the requirements of most codes as they include a thermal barrier to reduce heat flow. However, as building codes have evolved a new generation of curtainwalls has been developed to address higher performance requirements.
Curtainwalls now must incorporate more advanced forms of thermal barriers to greatly reduce energy flow through the framing product. Often referred to as advanced systems, they increase the interior surfaces of the framing system so that occupants can be more comfortable when sitting near them. They also greatly improve the system’s resistance to condensation and improve the building’s thermal envelope to reduce energy demands. Over time, these systems will become the new standard of curtainwalls.
Determine the desired exterior aesthetic
Only curtainwalls can support foursided captured, two-sided captured and four-sided structurally glazing applications. All three options provide the same level of daylighting; the difference is in the façade’s exterior appearance. A four-sided captured system mechanically captures the glass to the structural members, providing the designer with an opportunity to customize the exterior grid and achieve a unique element on the building’s façade.
Two-sided captured systems mechanically capture the insulating glass unit to the structural members along two sides of the unit and use a chemical bond, such as structural silicone or structural tape, on the other two sides. The designer has the same options available in customizing the exterior metal covers to achieve unique design traits along two sides of the glass.
Four-sided structurally glazed curtainwalls have increased in popularity with the advancement of structural silicone and structural tape systems. This method relies on a chemical bond to attach the glass to the structural framing members. Contractors typically apply structural silicone sealant or structural tape between the insulating glass unit and framing system to provide a system that can resist adhesive and cohesive failure for the specified design pressure. This method provides the appearance of a solid glass wall on the building’s façade that becomes part of the building’s identity.
Evaluate the Installation Method
There are three basic types of curtainwall installation methods: stick built, pre-assembly (screw-spline), and unitized. Each system offers benefits and limitations that must be considered.
Stick built systems are pre-fabricated in a controlled environment and shipped to the job site in pieces. Field labor then puts these pieces together based on a set of “tag drawings,” which identifies where each “tagged” piece goes on the building. This method requires strong material management on-site so that material delivered is organized and positioned strategically to maximize field labor efficiency. Another option is how the glass will be installed: from the exterior (outside glazed) or from the interior
(inside glazed). Outside glazing provides some level of efficiency because staging of the glass is less burdensome. However, one must have the capability of staging the building exterior to set the glass, so typically this option is only used on lower levels of a building. Inside glazing allows the contractor to stage the glass on each floor so that the glass can be installed into the glazing system from the inside. This is commonly used on high-rises and where access to the outside of the façade is limited.
Pre-assembled curtainwall systems are typically constructed from screw-spline curtainwalls. The basic geometry is the same with the exception of the vertical mullions having reveals in the back face of the mullion due to the vertical mullion being split. These systems are pre-fabricated and preassembled in a controlled environment and shipped to the job site in ladders. These ladders are lifted into place and anchored to the structure to await glass installation. Depending on the size of the units and available on-site lifting equipment, units may also be pre-glazed. In this case, the head and sill members of the curtainwall will feature a filler plate in the mullion to allow anchorage of the system. This is the most efficient installation method and allows rapid dry-in of the building envelope once the units are on-site.
Curtainwalls evolve to meet market needs
Curtainwalls are an essential part of the overall façade since it maximizes daylighting and allows occupants to connect to the environment and live healthier and happier lifestyles. Their evolution to improve the speed and efficiency of installation, meet new design challenges, and improve their overall performance keep curtainwalls an important part of a commercial buildings façade.
Mike Turner is the vice president of marketing at YKK AP America Inc., Austell, Ga. For more information, visit www.ykkap.com.com.