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A previous edition of Explainer described how exterior sun-shading devices, or brise soleils, have the ability to greatly reduce the solar heat gain of a building. When this particular architectural element is used in tandem with a double-skin facade, energy performance is optimized. Consisting of two building envelopes, an outer and inner layer, a double-skin facade creates an intermediate space that serves as a ventilating cavity, supported naturally or mechanically. The system acts as a thermal buffer that moderates occupant comfort, promoting air flow through the cavity and reducing energy consumption by providing heat in the winter and shading in the summer.
The concept of the double-skin facade was first explored and employed by Swiss-French architect Le Corbusier, who inserted heating and cooling pipes between large layers of glass, a system he called a mur neutralisant (neutralizing wall). Architects experimented with the system around the world but it never quite penetrated the industry to reach mainstream status. However, a recent drive for energy-efficient and environmentally friendly buildings has sparked a renewed interest in double-skin facades, with high-profile skyscrapers like 30 St Mary Axe and Shanghai Tower (above) adopting the practice.
Compared to a conventional glazing configuration, double-skin facades achieve a higher insulation value, helping to regulate the temperature of a building while improving on acoustic separation as well. Solar heat gain captured within the cavity between the inner and outer skins can be circulated throughout the occupied space to offset heating requirements in cooler climates or times of the year, while the cavity can be vented out to reduce heat buildup in warmer climates or times of the year. The efficiency and performance of the system is highly dependent on consistent maintenance.
The 1998-completed, 20-storey Stadttor in Düsseldorf, Germany, is another building where the technology is employed. In the image below, edges of both the outer and inner skins can be seen when looking through a corner of the building. Designed by Petzinka Pink und Partner, the building also features a 15-storey atrium within. Natural ventilation in the cavity between the skins and in the atrium allows windows to be opened throughout the structure for access to the moderated air.
The former Occidental Chemical Center in Niagara Falls, New York, below, essentially a nine-storey glass cube, implemented the first double-skin facade in North America in 1980. An independent energy analysis predicted that the structure would use only two percent of a conventional building's energy for winter heating and 19 percent annually for cooling. Grossly inadequate maintenance, however, meant that the mechanized louvers became nonfunctional, while air-intake grilles were covered to prevent the cavity from accumulating dirt and particulates from a nearby excavation site. The system was effectively rendered useless and now serves as a cautionary tale for owners who habitually ignore and defer building upkeep.
Critics contend that similar insulation values can be attained by using conventional high-performance, low-e windows, instead of having to sacrifice usable floor space for the cavity. The material and design costs of enacting the system can also be prohibitive; as a result, double-skin facades continue to be found almost exclusively on high-profile and big-budget projects.
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From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We are publishing or updating and republishing Explainer on a weekly basis. This article is an update of one by Marcus Mitanis that was originally published in 2017.
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Do you have other planning terms that you would like to see featured on Explainer? Share your comments and questions in the comments section below!
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