Double skin façades. Almost a self-explanatory name for façade systems consisting of two layers, usually glass, wherein air flows through the intermediate cavity. This space (which can vary from 20 cm to a few meters) acts as insulation against extreme temperatures, winds, and sound, improving the building's thermal efficiency for both high and low temperatures. Perhaps one of the most famous examples of double-skin facades is Foster+Partners' 30 St Mary Ax Building, "The Gherkin." The airflow through the intermediate cavity can occur naturally or be mechanically driven, and the two glass layers may include sun protection devices. While the concept of double-skin façades is not new, there is a growing tendency for architects and engineers to use them. Particularly in skyscraper design, they are favored for their transparent façade, thermal and auditory comfort, reduced air conditioning costs, and elimination of the need for window-specific technologies.
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