In the picture above, the older buildings mostly have brick or limestone-veneer facades, while the new buildings mostly have glass facades. That’s partly the result of changes in architectural styles over the course of the twentieth century, party the result of advances in glass technology, and partly the result of construction economics. What’s notably missing from that list is energy use, which has only recently become an issue that has been discussed as a public concern. Buildings that are wasteful of energy used to be seen as problems for their owners; they are now seen as environmental problems.
The simple fact is that glass is naturally a terrible insulating material, and the cleverness of the building industry in making insulating glass doesn’t improve the situation all that much. There are ideas that can be used to turn glass curtain walls from huge energy sinks into less-bad energy sinks; similar ideas can also be used to turn heavier materials from fairly good insulators into great insulators. Thanks to recent research, we can now speak about this issue quantitatively.
New York’s Local Law 84 has had owners of big buildings in the city recording energy use. The benchmarks can then be used as the basis to see how things are changing. When the data was first examined, it became clear that the first generation of glass curtain-wall buildings had the worst energy-efficiency.
Energy audits of the city have also shown that buildings are our primary contributor to greenhouse gases. We rely less on cars (per capita) than any other city in the country and we have little heavy industry, so buildings are what’s left. That, of course, means that improving our energy efficiency means looking at buildings, and that may mean looking at the use of glass curtain walls. So the stylistic goals and unobstructed views that can be met by using glass curtain walls are in conflict with reducing energy usage from buildings.