Prior to World War II, most skyscrapers had walls of stone or masonry. This was partly a holdover from the days when buildings were built with load-bearing exterior walls. The development of the steel frame at the end of the 19th century allowed buildings with non-load-bearing exterior walls, but codes were slower to change than technology, and still often required a thick layer of stone, brick, or terra cotta on the exterior. But by the late 1940s and early 1950s, building codes were beginning to omit these requirements.
As codes were changing, other technological developments were making thin exterior walls made of metal and glass practical. Air conditioning was becoming common, making it possible to cool buildings with large expanses of windows that might otherwise get too hot in the summer. Aluminum production had risen enormously during the war due to the needs of the aircraft industry, driving down its cost, and after the war manufacturers hunted for new markets that could absorb some of this capacity. Aluminum building cladding and window framing soon became an important new market. [...]
Glass, too, was getting cheaper. In the 1950s, British glass manufacturer Pilkington invented the float glass process, which produced glass by casting it on a pool of molten tin. The resulting surface was nearly defect-free, eliminating the costly grinding process flat glass had previously required and greatly reducing the cost of high-quality window glass. Between the late 1950s and the 2010s the cost of flat glass fell by 75% in inflation-adjusted terms.
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A glass and metal curtain wall wasn’t necessarily all that much cheaper than one made of brick in terms of the materials themselves, but it was much thinner and lighter. Its thinness meant that for two equally sized floor plates, the curtain wall framed one would have more rentable square feet than the stone or brick one. This more than made up for the fact that the thin curtain walls had worse insulation and were more expensive to heat and cool than masonry walls.
Similarly, the fact that a glass and metal curtain wall was so light meant that less structural framing was required to support it. Beams and columns could be made thinner, foundation sizes reduced. Not only did this reduce the cost of the building itself, but it reduced the cost of constructing it: all else being equal, a lighter structure is easier and cheaper to erect.
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The elimination of ornament also comes down to economics. As we noted earlier, developers place a great deal of weight on what tenants want, and what they’re willing to pay for. And the reality is that while tenants care a great deal about what the inside of the building is like, they pay much less attention to the exterior of the building. [...]
From the article:
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