Introduction and Overview

The Importance of Windows

Windows are one of the most significant elements in the design of any building. Whether there are relatively small punched openings in the facade or a completely glazed curtain wall, windows are usually a dominant feature of the building's exterior appearance. Windows can appear highly reflective, darkly opaque, or transparent, revealing or hiding activity within the building. Their color, transparency, and reflected patterns can change with the time of day and weather.

Although exterior appearance is important in architectural design, the traditional purpose of windows is to provide light, view, and fresh air for the occupants. As completely sealed, mechanically ventilated, and electrically-lit commercial buildings became the norm in the last half of the 20th century, the importance of windows in meeting the needs of occupants was diminished. There is a growing recognition, however, that even though light and air can be provided by other means, the benefits of windows are highly valued and contribute to the satisfaction, health, and productivity of building occupants. In addition to the trend toward more human-centered design, there is an urgent need for significant improvements in building energy performance in the immediate future.

The challenge in designing facades and selecting windows in commercial buildings is balancing many issues and criteria. Technical issues such as structure, moisture control, acoustics, and security require complex tradeoffs--cost is always an concern. Increasingly, costs are being viewed in a life cycle context that accounts for the impact of a window on long term operational, maintenance, and replacement costs as well as the initial expense. A critical concept that weaves together all of these concerns is high performance design, also referred to as sustainable design or green design. Generally, high performance design is intended to produce buildings that are energy efficient, healthy, economical in the long run, and use resources wisely to minimize the impact on the environment. An important concept to achieve these goals is integrated design that regards the entire building and its occupants as an interactive system.

The purpose of this web site is therefore to provide designers with more complete information on the energy, interior environment, technical, and life cycle cost impacts of window design decisions in commercial buildings. To do this, the current advances in window technology and tools for evaluating choices must be understood. The building industry has been in need of a comprehensive reference that both describes the fenestration design options and the performance of such systems in commercial buildings. This web site provides such critical information and performance data so that designers may begin to understand the implications of design choices on building performance. It is not enough to know that window choices have an impact on energy use and environmental quality -- the critical question is to what degree compared to other conventional design options? A fundamental barrier to the implementation of high performance facade design is this lack of information and knowledge, particularly at the early design stages, and the lack of design tools that allow designers to quickly understand complex, interrelated building performance issues.