Building envelope
The building envelope is a crucial architectural element that serves as the barrier between a building's interior and the external environment. It encompasses various structural components, including walls, roofs, doors, and windows, which work together to provide protection against weather elements such as wind, rain, and sunlight. This enclosure plays a significant role in regulating indoor temperatures, with its design tailored to suit specific climates; in hot areas, it helps reduce the need for cooling, while in colder regions, it prevents heat loss. Furthermore, it contributes to indoor comfort by managing daylight, sound insulation, and moisture control.
The materials used in constructing the building envelope can range from natural materials like wood and stone to advanced synthetic products, influencing its thermal and acoustic properties. Effective design is essential, as it can mitigate the impacts of solar radiation, precipitation, and wind, which can lead to condensation and dampness if not properly addressed. Historically, various societies have adapted their building envelopes to cope with local climatic conditions, a practice that continues today with modern technology allowing for more sophisticated solutions. Ultimately, a well-designed building envelope not only enhances comfort and energy efficiency but also minimizes the environmental impact of heating and cooling operations.
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Building envelope
Summary: A building envelope is the enclosure of a building that separates the internal spaces from the external environment and provides physical protection from wind, rain, sun, and other weather events.
The structures that separate the interior and exterior of a building are collectively known as the building envelope, sometimes also called the building enclosure. Essentially, this concept defines the distinction between interior, environmentally conditioned space and the exterior environment. In hot climates, the building envelope protects internal spaces from excessive heat and moderates the need for mechanical cooling, whereas in cold climates it serves to prevent heat from escaping out of the building and helps to reduce the indoor space heating required. In addition to maintaining thermal comfort, a building envelope serves the functions of providing daylight to indoor spaces to limit the artificial lighting needed in the daytime, sound insulation of the interior from the external environment, and control of moisture or humidity for maintaining indoor comfort. Structural integrity and aesthetics of a building also depend on the design and materials used in the construction of the building envelope. According to the US Department of Energy, about 30 percent of a building’s energy consumption occurs in the building envelope.
The elements of a building envelope include walls, floors, roofs, doors, and windows directly in contact with the external atmosphere. Each of these elements is made up of assemblies of materials and individual components, which determine collectively the desired properties of the building envelop. Each assembly may consist of natural materials, such as stone and wood, or manufactured and highly processed materials, such as cement, steel, and specially engineered glass. For example, a building’s fenestration (window structure) may be entirely of specialist glass such as a structural glass cladding with a supporting steel structure, or traditional windows that are made up of wood or metal framing with single-, double-, or triple-layered glass panes. Thermal properties of each of these elements are aggregated to give a collective heat transfer coefficient, which indicates how well an assembly conducts heat, expressed as the U-value or U-factor of the window or cladding assembly. Sound insulation is also a collective property of the assembly, whereas the moisture-repelling capability depends primarily on the properties of the external surface and on the detail design of the assembly.
The main climatic (that is, diurnal and seasonal) changes that affect a building envelope are solar radiation, precipitation, and wind. These factors have an impact on both the external and the internal surfaces of the building envelope, although internal surfaces are affected mostly by seasonal changes because they are sheltered from daily climatic variations. Solar radiation in the daytime is responsible for heating the external surfaces of the building (facades), enabling them to radiate heat until arrival of cooler air in the evenings and night. The temperatures of the external facades thus fall to below the ambient temperature of the surrounding humid air, resulting in condensation on the facade surfaces. External building surfaces also directly receive moisture from the precipitation falling on them. Such water-soaked external surfaces may have the moisture driven to the internal layers of the envelope elements by the wind, causing interstitial condensation.
Repeated occurrences of external surface condensation and interstitial condensation, leading to internal dampness in the building envelope, can affect indoor air quality and hence internal comfort. Similarly, overheating of the building envelope will cause heat to be conducted to the internal surfaces of the envelope elements, causing overheating of the indoor spaces. Such weather-related effects can be managed by designing the elements of the building envelope to withstand the expected climatic effect on them. For example, adding insulation to the external walls prevents overheating of the internal spaces by preventing heat from flowing from the external heated surfaces to the interior. Similarly, designing an effective rain-screen cladding for the external walls can minimize the impact of precipitation on external walls, thus reducing moisture-related problems indoors.
Design of the building envelope to mitigate extreme climatic effects is not a new concept and has been conducted by traditional societies through the ages. Even though the desired functions of the building envelope remain the same—to prevent overheating, dampness or moisture, and excessive cold in the internal spaces—the methods of achieving these goals through the design of the building envelope have significantly changed. The materials used in the construction of building envelope elements are now highly advanced and suited to today’s high-rise and technically complex structures, in contrast to the natural and local materials used in traditional low-rise, passive architecture.
It is worthwhile to remember that achieving indoor comfort by mechanical means, such as air-conditioning and mechanical forced-air heating and ventilation, can overcome some weather-related problems. However, the energy used in mechanical systems is an expensive way of dealing with climate effects that can be completely eliminated, or at least reduced to a manageable level, through effective design of the building envelope. Passive environmental design of buildings not only helps to make healthier spaces to live and work but also reduces the carbon impact caused by the day-to-day operations of buildings.
Bibliography
American Institute of Architects. The Building Envelop. Washington, DC: American Institute of Architects, 1982.
Brookes, Alan, and Chris Grech. The Building Envelop: Applications of New Technology Cladding. Boston: Butterworth-Heinemann, 1996.
"Building Envelope." Better Buildings, 2024, betterbuildingssolutioncenter.energy.gov/building-envelope. Accessed 29 July 2024.
Kubal, Michael. Waterproofing the Building Envelop. New York: McGraw-Hill, 1993.
Morales, Arthur. The Building Envelop. Master’s thesis, New York Institute of Technology, 1999.
“Building Envelope Design Guide." National Institute of Building Sciences, 2024, www.wbdg.org/design/envelope.php. Accessed 29 July 2024.