If you wear a hat that’s 12 inches higher than the top of your head, does that make you a foot taller? If you’re a building, the answer may be “yes.”

The business of measuring the height of buildings is not as elementary as one might expect. Concepts that seem pretty straightforward, such as “the ground” and “the roof,” are actually fairly nuanced.

For example, in many cities, the ground is not perfectly flat, and one street will often be higher than the next. In a place like San Francisco, this can mean a difference of several stories, but even in relatively flat cities like Chicago, it can still mean a difference of several feet. If the building has multiple doors on all four sides, or even two sides, at different levels, where do you measure from? The truck loading dock? The entrance to the observation deck? The fire exit?

At the top, things get even more complicated. Which “top” are we talking about? The highest floor where people can stand in an enclosed space? The interior ceiling of that space? The top edge of what is perceivable as the “roof” from the ground? What about spires, crowns, and antennae that give so many of our most famous buildings their character; are those part of the building?

Establishing Criteria for Measuring Height

The Council on Tall Buildings and Urban Habitat (the Council) was founded in 1969 to answer some of these measurement questions. At the same time that the U.S. and U.S.S.R. were leapfrogging each other with technological innovations on the way to the moon, so too were building designers, by coming up with new technologies to make buildings substantially taller than before.

About 40 years ago, the Council decided on a set of criteria that would settle the score between those who would claim they had the “tallest building in the world,” the “tallest hotel in North America,” the “highest observation deck,” and so on. With a few minor modifications, these criteria have held steady.

These are the three basic categories decided:

  1. Height to tip: Height is measured from the level of the lowest, significant open-air, pedestrian entrance to the highest point of the building, irrespective of material or function of the highest element (i.e., including antennae, flagpoles, signage and other functional-technical equipment).
  2. Highest occupied floor: Height is measured from the level of the lowest, significant, open-air, pedestrian entrance to the finished floor level of the highest occupied floor within the building.
  3. Height to architectural top: Height is measured from the level of the lowest, significant, open-air, pedestrian entrance to the architectural top of the building, including spires, but not including antennae, signage, flag poles or other functional-technical equipment. This measurement is the most widely utilized and is employed to define the Council’s rankings of the “World’s Tallest Buildings.”


Sculptural-Iconic Skyscrapers Complicate Matters

From the 1970s to the mid-1990s, when the vast majority of buildings being built were flat-topped, this system worked pretty well. However, beginning in the late 1990s architects began designing skyscrapers in more eccentric shapes than ever before, making what would seem like rudimentary decisions—such as where the “top” of the architectural height actually is—much more difficult. In recent years, these arguments have grown ever more contentious.

Environmental Concerns Rise Alongside Height

Buildings contribute to about one-third of all landfill waste on earth and consume about 40 percent of the planet’s energy. Concerns about climate change and the total amount of energy it takes to operate a building, as well as its embodied energy—the amount of energy it takes to make the building—have risen. And yet, curiously, it appears that the number of buildings designed with parts that have no purpose other than to achieve height, has risen too.

Introducing “Vanity Height”

In September 2013, the Council released a study called “Vanity Height: The Useless Space in Today’s Tallest.” The conclusions were stunning. The tallest building in the world, the Burj Khalifa in Dubai, has 29 percent “vanity height.” That is, 29 percent of the 828-meter building does not contain occupiable space. If the non-occupiable part of the Burj Khalifa were placed on the ground, it would be Europe’s 11th tallest building, all by itself. The biggest offender was the 321-meter Burj al Arab, also in Dubai, 39 percent of which is non-occupiable by humans.

Test Case of Criteria: One World Trade Center, New York City

In November 2013, The Council’s Height Committee convened to rule on the height of One World Trade Center (One WTC), the office tower in New York City. Designed to rise to 1,776 feet—in commemoration of the year of American independence from Britain—the structure would be capped by a spire extending 408 feet from the top of the roof.

The spire would also make the new One WTC the same height as the roof of the original building, destroyed by terrorist attack on Sept. 11, 2001. It was hugely important to the builders, New Yorkers, and the American public that this symbol of resilience be recognized for its intent. That meant it had to be 1,776 feet high. But was it?

It might not have been much of a question if the design of the tower had not changed during its tortuous path to fruition. The original spire was a distinctively solid mass that completed the architectural expression of the building – you could literally make it out from miles away. Then, budget concerns stripped the cladding from the spire, leaving something more spindly in nature. Now it looked more like an “antenna” – even the architect said so. According to the Council’s criteria, that would make a huge difference in its height – 408 feet, to be exact. That would mean its “height to tip” would be different than its “height to architectural top.” The symbolic gesture of 1,776 would be lost.

The One WTC spire was always intended to support broadcast equipment along some of its length, in both design schemes. In fact, the cladding that came off – supposedly saving millions of dollars – was called a “radome,” short for “radar dome.” The idea was that the folded plates of the radome would protect the structure and broadcast equipment inside. At the very top of the spire was a beacon, which was intended to remind viewers of the old lighthouses that once welcomed new Americans to New York Harbor. With the design change, the beacon stayed, and the radome was cut out. So what was that thing on top of the building?

It all comes down to “intent.” David Childs, the building’s architect, flew to Chicago to meet with the Height Committee of the Council to explain his intention and how he believed it had been executed. After a brief presentation, the Height Committee debated and concluded that, because the spire, even in its altered form, was intended as a permanent part of the building, never to be removed or altered, it would count toward One WTC’s “height to architectural top” – 1,776 feet.

This was not a judgment of the artistic merit of the spire. Instead, this was simply an act of defining it as one thing and not another. The structures on top of the Willis Tower (formerly Sears Tower) are antennae, and are not part of the building. Though they may seem immutable—any kindergartner would draw them as part of the silhouette—in fact, the antennae on top of Willis Tower have been altered several times to accommodate changes in broadcast technology. Through this distinction, the Willis Tower lost its designation as the “tallest building in the United States.” And yes, both the “spire” of One WTC and Willis Tower’s “antennae” support broadcast equipment. But the “spire” is not an antenna because it is meant never to be removed and is a critical part of the building’s architecture.

In the media, this was played as the central dramatic conflict of the issue, but One WTC was not designed to be 1,776 feet tall so that it could outstrip the “tallest in the U.S.” title. And the “world’s tallest” title had been lost by the U.S. in 1998, when Sears ceded it to Petronas Towers, in Kuala Lumpur, Malaysia, also on the basis of the “spire” distinction.

Why – and How – Should We Build Tall?

The bigger question is this: Why care about these statistics? Isn’t this all kind of silly? Perhaps so.  But isn’t building an entire category of economic enterprise on the practice of watching people toss a ball and run into each other on a field also silly? People like to see big achievements, and they like records. There are few better ways to get your city on the map.

Furthermore, how does the present interest in environmentally-responsible design reconcile itself into our skylines? Should the criteria for what is “tallest” be altered so that developers are discouraged from building “vanity” crowns and spires? Do we want to live in a world with only flat-topped buildings that are pure physical manifestations of economic equations? Do we want our buildings to be Priuses instead of Ferraris? To build tall in a way that maximizes energy efficiency, pencils out economically, and still has the jaw-dropping power of an icon – that is our challenge.

Further Reading:

Media coverage of the vanity height report.

Media coverage of the One World Trade Center Height Ruling.

Image credit: Daymin via flickr