Tips for Selecting Higher-Performing Windows

Oct. 1, 2007
Balance exterior and interior architectural elements and technical issues when selecting windows that work

By Greg Lusty

With the explosion of sustainability, building design has become more of a challenge. We now need to design commercial buildings with more glass and larger openings to allow for more daylighting. Higher-performance glazing is being specified in commercial buildings. Now, more than ever, glazing energy-efficiency values typically only found in residential windows are being specified in commercial applications. Many specifications are even referencing ENERGY STAR® window U-value numbers as low as 0.35. The challenge in designing façades and selecting windows in commercial buildings becomes a balancing act between the exterior and interior architectural requirements and various technical issues such as energy efficiency, structural integrity, moisture control, acoustics, and security.

These marketplace and building trends have created quite a challenge for window manufacturers. The size, configuration, and energy-efficiency demands on windows have led to the development of various technologies that can drastically improve the energy efficiency of a window system. The majority of the focus in the past has been on technologies that improve the energy efficiency or solar heat gain of the glass, such as tints, hard- and soft-coat low-E coatings, and gas fills. More recently, manufacturers have been focusing on other areas of the window system. Much like the design of a green building, the design of a window system is only as good as its weakest link.

In improving window performance, consider the following:

  1. Warm-edge insulating glass. Warm-edge technology is one technology that is helping window systems contribute to the overall energy efficiency needed in today's sustainable design. Warm-edge spacers are primarily used to provide a better thermal insulation between the two lites of glass in an insulated glass unit. The most effective warm-edge spacers do not have any metal in the spacer itself. When a nonmetallic material is used as a thermal separator, less heat or cold will pass from one side of the glass unit to the other, especially at the edge zones, when compared to an insulating glass unit with a metallic spacer.
  2. Thermal barrier technology. Another important factor when looking at the overall energy efficiency of a window system is the thermal barrier system. This is especially important in commercial applications where aluminum windows are often used. There are a number of methods of creating a thermal barrier in the frame of an aluminum window. One of the most efficient and effective technologies is a glass-reinforced polyamide system that allows for a larger gap between the exterior and interior of the frame, and can significantly improve the overall energy efficiency of the window system when compared to a traditional polyurethane thermal break. Another interesting non-energy-related benefit is that this system allows architects/designers the ability to specify different exterior and interior colors or finishes.

Commercial aluminum windows have traditionally been thought of as less energy efficient than alternative materials such as wood, vinyl, and fiber glass. With the implementation of thermal-improvement technologies like the ones mentioned, aluminum windows have the ability to reach U-values only attained previously by other materials.

Windows can have a positive effect on much more than just energy bills - they can contribute to the satisfaction, health, and productivity of occupants in buildings as well. Windows are also increasingly being viewed in the life-cycle context that accounts for their impact on long-term operational, maintenance, and replacement costs. Yet the challenge continues in communicating the value of installing these highly energy-efficient products. Even with the dynamic growth in green building and LEED certification, owners, contractors, developers, and architects are hesitant to invest in superior products if it means they have to spend more. The primary challenges have been communicating and demonstrating return on investment.

Energy-efficient glazing systems do lead to a return on investment. The key to realizing that return is finding the right product for your project. Involving a window manufacturer early on in the project will only increase your chance of successful sustainable design. 

Greg Lusty is product manager at TRACO (, Cranberry Township, PA.

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