It may not feel like it, but we’re likely experiencing the largest construction booms in history. According to one estimate, the world will build the equivalent of a New York City every month from 2020 to 2060.
Even this may not be enough to meet the growing demand for housing. The United Nations estimates 96,000 affordable units should be built a day to house the three billion people who will need them by 2030.
Many countries facing explosive population growth are creating entirely new cities that combine environmental ambition with striking architecture. Egypt is constructing a capital east of Cairo for 6.5 million residents featuring Africa’s tallest skyscraper. To take the pressure off Greater Jakarta’s 30 million residents squeezed by rising seas, Indonesia is building a new capital on the island of Borneo.
Perhaps most famous of all is Saudi Arabia’s NEOM, which includes a mountain ski resort, a floating logistics hub and a city known as “the Line” with two parallel skyscrapers connected by walkways that will stretch across a desert and mountains. Though the government recently scaled back the first phase of construction, it has allocated billions of dollars for the project, which could one day house some nine million people.
The ultimate statement of ambition, wealth and technological advancement, the city is planned to be about 655 feet wide, 1,640 feet high and some 106 miles long — a distance about eight times the length of Manhattan Island.
The Line offers a hedonistic vision of city living. In renderings, families picnic on sky bridges above canyon-esque atria. Lush greenery cascades from skyscrapers stretching out to the horizon as far as the eye can see. And the project promises a version of urban sustainability most cities can only dream of: no roads, cars or greenhouse gas emissions from transport or electricity.
But the Line, for all its chutzpah, should not be our model for sustainable city living. There are far better ways to build, informed by everything we already know about materials and design. The cities of the future should experiment with architecture, but in service of making spaces more livable and sustainable, not simply iconic.
While Saudi Arabia’s decision to build a very tall linear city may seem bizarre, there are clear benefits to stacking buildings atop one another and connecting them with walkways at different heights and transit lines. Residents can get from one end of the city to the other in just 20 minutes without ever setting foot in a car.
What’s more, by stacking the city vertically, the density of the Line would be a heady 685,000 people per square mile, making it the densest city on earth, far denser than the Mong Kok district in Hong Kong, which has some 340,000 people per square mile. This hyperdensity gives the Line a tiny physical footprint, leaving 95 percent of the surrounding region conserved for nature.
But while the Line is dense, I’d hardly call it compact. Its giant mirrored glass facade will create a roughly 33-square-mile wall across the desert, a substantial risk to migratory birds. Villages have also been demolished to make way for its unrelenting linear footprint. Stacking the city up into the sky isn’t cheap either — reports suggest the Line may cost more than twice as much per square foot as conventional skyscrapers in the Middle East. This is not a model for affordable housing we should replicate elsewhere.
The Line’s height also creates its own environmental problems. Tall buildings require more structural materials — usually concrete and steel — to resist the wind loads that increase with height. Manufacturing these materials has a significant impact on the climate. Cement, for instance, is responsible for around 8 percent of all carbon dioxide emissions, while steel generates around 7 percent of the total.
The Line’s design calls for vertigo-inducing cantilevers and even a gravity-defying stadium spanning two buildings hundreds of feet above the ground. In all, it will require a truly colossal quantity of materials, with emissions likely much higher than those produced in building a typical city — not something to emulate.
If not supertall, what form should new cities take? Some researchers suggest mid-rise high-density buildings (think Paris or Barcelona), while others support a height of 18 to 20 stories for a city of 10 million. This doesn’t mean we shouldn’t build taller buildings. It means we should avoid heights as dizzying as the 1,640-foot-tall Line.
When it comes to materials, we should prioritize timber, stone, rammed earth and even cork, which are all better for the climate than concrete or steel. Regulations in France mandate that all new public buildings should be built with a least 50 percent timber or other natural materials, for instance, and now whole new developments there are being built from wood. When combined with some steel and concrete, timber can even be used to build skyscrapers.
Access to timber in countries such as Saudi Arabia might be limited. But in neighboring Yemen, the 500-year old city of Shibam shows how mud brick can be used to create buildings at least seven stories high. Architects are deploying rammed earth and mud brick in all kinds of contemporary ways, such as at the wonderful Hikma Religious and Secular Complex in Niger. We can also make prefabricated walls out of these natural materials for multistory apartments.
