In most of the world’s big cities, the demand for land and space far outweighs the amount of land and space that is actually available. A high-rise is a building that helps to ease the tension between these competing demands. The high-rise is characterized by its height – usually at least twelve floors — and its density. A building that takes up the space of but a modest apartment house or office building in terms of actual landmass can easily house hundreds of units if built straight up.
When high-rises are used to house apartments or individual condo units, they are often referred to as “multi-dwelling units,” or MDUs. In Europe, they are also frequently called “tower blocks.” The regulations and restrictions for where high-rise housing units can be built, what sorts of safety precautions must be made for fire escapes and other evacuations, and the residential laws with which the building must comply vary by city. Some cities tightly regulate high-density housing, while others allow builders and rental companies much more freedom.
High-rise structures are also popular settings for urban offices. While an office building in the suburbs may sit on a campus of several low-lying buildings, it is not uncommon for city office towers to reach 60 or 70 floors. High-rise offices are synonymous with skyscrapers. One of the tallest high-rises in the world is the Burj Khalifa in Dubai, United Arab Emirates. The Burj Khalifa is 2,717 feet (828 meters) tall, and contains 206 floors. Slightly shorter than the Burj Khalifa, another of the world's tallest building is the Taipei 101 tower in Taipei, Taiwan, which stands at 1,670 feet (509 meters), and held 101 floors.
The benefits of high-rises, at least from the perspective of economy of space, are obvious. By maximizing vertical space, cities can accommodate tremendously more people than if they were limited to their horizontal landmass. More residents means more business and more consumption; more offices means more jobs and a more robust economy.
Urban planners have tried to maximize vertical space with high-rises for centuries. Still, much of the efficiency of a true high-rise depends on certain technologies, many of which are more modern. Steel framing was the first tool to revolutionize the art of building high-rises. In order to sustain floor after floor after floor, a building must have a structure that can withstand a tremendous amount of weight, and will not be compromised by a relatively high center of gravity. Of course, for towering floors to be useful and accessible, there must also be an easy way for people to get to them — which generally requires an efficient elevator system.
Some of the biggest criticisms of high-density buildings, whether they be offices or housing units, is evacuation safety. No matter how efficient a building’s elevators are, there is no realistic way for any elevator system to be able to carry every one of a tower’s many residents in a limited amount of time. Also, in most emergency situations, including fires, buildings lose power, and elevators do not operate. Even with emergency staircases, it is usually impossible for individuals on floors above seven or eight to be able to walk out of an occupied burning high-rise before it fills with smoke.
High-rise disasters are relatively rare, and the efficiencies are generally believed to far outweigh the risks. Every major city in the world is home to a range of high-rises. High-rise living is often considered a quintessential city-living experience.