The importance of external windows in buildings
2026-06-10
In any architectural project, windows are one of the most important elements. Whether openings in the building envelope or continuous glazing in the form of a curtain wall, windows are usually the dominant feature of a building's exterior. Windows can be highly reflective, dark and opaque, or provide a transparent effect, revealing or hiding what's going on inside. The color, degree of transparency and nature of reflections in windows may vary depending on the time of day and weather conditions.
Although the appearance of windows is critical to the architectural appearance, their traditional function is still to provide occupants with natural light, views and fresh air. In the first half of the 20th century, as sealing, mechanical ventilation, and electric lighting technologies were introduced into commercial construction, the role of windows in meeting the needs of building occupants decreased somewhat. However, there is a growing recognition that although light and air can be obtained through other means, the benefits of windows for human comfort, health and productivity remain clear. Currently, in addition to the trend towards human-centric design, there is an urgent need to significantly improve the energy efficiency of buildings in the near future.
One of the challenges when designing curtain walls and selecting windows in commercial buildings is finding a balance between design and human issues, as well as numerous technical criteria and cost. Technical aspects include issues such as design, humidity control, acoustics and safety, all of which require difficult trade-offs. Gradually, along with the initial investment costs, life cycle assessments begin to take into account the costs of long-term operation, maintenance and replacement of windows. A new concept that brings all of the above factors together is high-performance design, also called sustainable design or green design. Overall, the goal of high-performance design is to ensure the long-term energy efficiency, health and economy of the building, as well as the efficient use of resources to reduce environmental impact. An important concept for achieving these goals is integrated design, in which the entire building and its occupants are considered as a single interactive system.
To do this, it is necessary to have some understanding of the current progress in window technologies and methods for assessing their performance. The construction industry requires comprehensive reference materials covering the selection, design and performance of operable windows in commercial buildings. This book provides important information and performance data in this area, helping architects and engineers understand how design decisions affect building performance.
It is not enough to simply know the impact of window choices on energy consumption and environmental quality. The key question is how much impact do windows have on these factors compared to other traditional design decisions?
A major barrier to high-performance window, door and curtain wall design is a lack of information and knowledge, especially at the early design stage, and a lack of tools and tools that allow designers to quickly understand the complex and interconnected characteristics of a building. Part of the basic knowledge required to create such tools and methods must be obtained by assessing actual existing buildings.
1 Energy saving
In addition to determining the building's appearance and interior environment, windows are one of the most important building components affecting energy use, peak energy demand and the environment. Solar heat gain and heat loss through windows account for a significant portion of the heating and air conditioning load of buildings. By providing natural light, windows can reduce electrical lighting loads if lighting fixture dimming is effectively controlled. Smart window design and selection can reduce peak electricity demand and air conditioning loads, thereby avoiding high electricity costs and reducing the need to build new power plants. In addition, high-efficiency windows have an impact on the building's utility systems: they not only reduce operating costs, but also make it possible to reduce the size of equipment, which saves capital investment.
Commercial building energy consumption accounts for 16% of total energy consumption in the United States (about 15.4 quadrillion BTU①, with total community energy consumption about 92.6 quadrillion BTU). Meanwhile, 1.1 quadrillion BTUs of commercial building heating and cooling energy consumption are lost through windows, while lighting energy consumption is 3.83 quadrillion BTUs. If we assume that 25% of lighting energy consumption (about 0.96 quadrillion BTUs) is due to natural light issues through windows, then the total annual energy consumption associated with windows is about 2 quadrillion BTUs. This means they account for about 2% of total community energy consumption and more than 12% of total commercial building energy consumption in the United States. If residential buildings are included, the total energy consumption through windows will reach 5 quadrillion BTUs, representing more than 5% of the total social energy consumption of the United States.
① Note: Quad = quadrillion BTU = 10¹⁵ BTU ≈ 34.8 million tons of fuel equivalent. Btu (Btu) - British Thermal Unit, the amount of heat required to heat 1 pound of water by 1 degree Fahrenheit, 1 BTU ≈ 1055 J.
2 Human-centered design
In the United States, many buildings continue to be designed with large interior spaces and relatively little glass area. Over the past 50 years, windowless office and school buildings have become commonplace. Even if there are windows, they rarely open and therefore do not provide natural ventilation. These windows are often equipped with tinted or mirrored glass to reduce glare and solar heat gain, but this also reduces the softness of the light and limits the view of those inside. This trend continues and sometimes even worsens. For example, glare can make working on a computer screen uncomfortable, leading to the need for even darker glass as a countermeasure.
Because light and air can now be obtained through electrical and mechanical systems, the traditional role of windows has been weakened, reducing their importance in most modern commercial buildings. Of course, this shift overlooks the key role windows play in creating healthy, productive, inspiring and attractive indoor environments, although these factors are sometimes difficult to quantify. Natural lighting has many characteristics that electric lighting cannot replace. Changes in the intensity, direction and color of light connect us to the weather, seasons and time of day. Window views, especially of wildlife, play an important role in maintaining people's physical and mental well-being, as well as improving their sense of orientation and space. The ability to open a window to breathe in fresh air not only gives building occupants a sense of control over their environment, but also establishes a connection with the outside world. In fact, windows add variety and sensory stimulation that is lost in a confined space.
In some European countries, legislation requires that all workers be kept a certain distance from the window and that the windows must be operable. Of course, achieving the many benefits such as natural light, views and natural ventilation is only possible with careful design, which must also prevent and control the potential negative effects of windows such as excess glare and reduced thermal comfort. Modern research shows that windows and natural light play an important role in creating a positive indoor environment, which in turn improves productivity and health.
3 Life cycle cost
Of course, windows are an important component of a building in terms of their cost. The initial investment costs for windows are usually higher than for opaque building envelopes of the same area, but demand or subjective requirements for certain types of windows often do not need to be justified. However, the more important question is how to justify the additional cost of increasing the glass area and using high-efficiency windows. The operating energy consumption and maintenance costs of a building typically exceed the initial investment costs by more than ten times. Moreover, the costs of construction for residents are many times higher than the costs during the operation of the building. The initial cost of windows influences many decisions, but compared to other aspects it is only a small part.
Because windows have a significant impact on building operating costs and the health, productivity and well-being of occupants, it is necessary to use a life cycle approach when selecting and designing windows. Life cycle analysis includes the impact of architectural design and material selection on economics, the environment, and human well-being. Window frames, glazing and sealants all have different service lives, so durability is a key factor in any life cycle analysis. However, windows typically have a life expectancy of 20–30 years and are more expensive and difficult to replace than other building systems, so maintaining energy efficiency throughout the life of the windows is also a fundamental aspect of their longevity.
