In “Why skyscrapers are so short” Brian Potter explains why the height of skyscrapers remains well below what it’s technically possible today, why height limits are far stricter than necessary, and why this matters.
Here is a brief summary:
Roman builders were capable of constructing buildings over 48 meters in height, about 13 modern storeys. The Colosseum is 48.4 meters tall, and the Pantheon 43 meters tall. Legal limits were sometimes lower to reduce the risk of collapse (which was apparently common). Augustus limited the height of buildings to 70 Roman feet, then further restricted by Trajan to 60 feet.
Two technologies allowed these limits to be exceeded. The first was the metal skeleton (first iron, later steel). In 1889, the Eiffel Towe reached a height of 300 meters. The second was the elevator, which made it feasible to reach those upper floors. These two developments dramatically increased the height that buildings could economically reach, enabling the construction of the first skyscrapers.
The impact of these technology changes are most clearly visible in New York and Chicago, two cities undergoing enormous population growth at the turn of the 20th century and which had no previous history of building height regulations. New York passed its first zoning code in 1916, which placed limits on building massing. Chicago had passed a maximum height limit of 39.6 m for buildings in 1893, which was adjusted several times over the next few decades.
The basic physical limitations on building height have not changed substantially since the early 20th century. In The Tall Buildings Reference Book, the authors state that under pure gravity loading, a steel-framed building could perhaps reach 3,000 meters in height, dropping by half once lateral requirements were taken into account. Modern legal restrictions on building size are complex and vary greatly depending on things like the type of building, where it’s being built, what materials are being used, what air rights can be secured, and what the jurisdiction (and the public) will approve.
Building height can be thought of as a technology for using a given plot of land more intensively, to squeeze more usable space out of it. Ideally, legal restrictions on building height would be just strict enough to properly account for the negative impacts of excess building height. But evidence suggests current legal restrictions are often far in excess of that.
Building height restrictions make us all poorer – not only do they cause a deadweight loss by artificially restricting the supply of available building space where it’s needed the most, but they also screen off the potential agglomeration benefits that accrue from increased density.
Reading Brian’s post, which I recommend, I can feel that building height is a beautiful metaphor for Mind The Post central hypothesis that we are performing as a society well below our collective potential.