Tall, Global and Sustainable
by Adrian Smith
We are often asked the question, “Why build tall?” What are the advantages and disadvantages in this typology and why do we see more and more tall buildings being built thorough out the world?
To answer this, let’s examine what is happening to the world’s population growth rate for some clues. As of this year, 2013, the world population reached 7,100,000,000 and is growing at 1.16 per cent per year. That equates to a net gain in worldwide population of some 80,000,000 people per year. Three countries—China, India and the United States—comprise over 40 per cent of the current world’s population. This staggering figure equates to the need for 9+ New York Cities (or 2 Argentinas or 3.4 Shanghais every year. Add to this that the world’s population is urbanising at an alarming rate—reaching the 50 per cent mark this year—and it is not difficult to see why the pressure to build tall is great.
How tall is practical and affordable? Our research suggests that buildings of three-to-four stories are inherently the most cost efficient when factoring in land use and cost, cost of construction, efficiency of floor plates and efficiency of structure. Taller structures need mechanised vertical circulation, concrete or steel structures, mechanical, electrical and plumbing shafts and multiple exit ways which all effect net to grow efficiencies and add to the net cost per unit. Increased density however does add to the compactness of urban environments and this can create a number of social benefits that offset costs. Accessibility to goods and services, cultural events, communal spaces for human interaction, and a live-work environment accessible by walking is often the result of an appropriately scaled high-density area.
How tall is too tall? This depends on the motivation of the person who initiates the tall building. We know that land cost is a factor and the more desirable the location, the more costly the land. The desirability factor fuels both land cost and the desire to provide as much space as possible for people to occupy. Often, this drives buildings to very tall or even supertall status. Uniquely, the reverse is also true. When a supertall tower is built, it will most generally increase the value of everything around it, putting pressure on adjacent sites to maximise their potential and develop tall structures. Views from within a tall building are also coveted and the higher the occupancy space the better the vista and the more valuable the space. This is generally truer in geographic locations that are predominantly flat like Chicago, New York or Dubai. Views on Central Park in New York or of the top of the Chrysler Building in Manhattan will demand substantially higher rents or prices than those with normal building-to-building views. Views from the top of the Burj Khalifa can be similar to those from an airplane and one can sometimes see the shadow of Burj on the clouds below. On a clear day it is possible to see the curvature of the earth.
Often supertall towers are designed purely to satisfy the ego of the owner but it turns out these towers are rarely built. The cost is simply too high and the task too demanding, even for the most egocentric of clients. Instead, the supertall is usually built for landmark status, either to give identity to the country, region or city within which it is built, or in some cases as a centerpiece for a large scale satellite city development. A world’s tallest proposal will always get attention for both developers and cities, and they have discovered that there is value and attention when building something tall in their city. Tall towers can be a financial bust to a developer who sets out to build just the tall tower, but they can bring great economic vitality to the surrounding city. This is especially true if there is little or no knowledge of the place prior to the construction of a world’s tallest tower. Examples of this are seen in Taipei, Kuala Lumpur and Dubai. Most world’s tallest observation decks will experience on average 1.5 million visitors per year just to see the views from these towers and tickets can cost as much as $130 USD.
There is considerable interest in building a mile-high tower sometime in the near future. The limiting factor in doing so seems to be the enormous initial investment needed and the absorption rate to fill a building that would need to be nearly 10 million square feet of usable space. A tower of one mile would need a base dimension of at least 500 feet, approximately the size of three city blocks of downtown Chicago. It would take approximately eight-to-ten years to complete construction of such an edifice. Still, it is possible with today’s technology to structure and elevator and service such a building.
The CTBUH (Council on Tall Buildings & Urban Habitat) reports that of the 59 supertall towers built in the last 20 years, all but three have been built outside the United States. Furthermore, they project this trend to continue into the future. In China, 56 supertall towers are currently under construction. This has little to do with economics and a great deal to do with city and national pride. Although China has thus far resisted the urge to build the world’s tallest tower, there is growing sentiment to do so. There is a strong rivalry to be the tallest in China among cities and developers of supertall with Shanghai, Shenzhen, Wuhan and Chengdu all building supertall.
At over 1000 meters high, The Kingdom Tower—designed by Adrian Smith and Gordon Gill Architecture—is now under construction and due to be completed within six years. It will be the next world’s tallest building. The purpose for this tower is to be a symbol of welcoming to the City of Jeddah and to be the centrepiece for a new Kingdom City. This will be a planned community on 5.3 million square meters to house the Kingdom’s growing population.
Over the last five years the live-work satellite city has emerged as a potential answer to the tremendous population growth in the emerging economies of China, India, Saudi Arabia and Dubai. These new communities are city-sized high-density developments for 100,000 to 150,000 people, who will live, work, recreate, learn and shop, all within walking distance to each other, and occupy only one square kilometre of land area. They are envisioned to be at the edge of major established urban population centres that have reached their peak of development within the core. In many cases there can be several of these ‘satellites’ surrounding the city. Each can be connected to the other by an outer rapid transit connector which gets connected to the city transit system at some point.
One primary factor to the success of these cities is that they are pedestrian-oriented with minimum ownership of automobiles, and minimum parking demand and availability, thus reducing costly parking structures and allowing for more car-free environments. This factor also greatly reduces the carbon footprint of these communities. These satellites are being designed to be highly sustainable, taking advantage of mass construction techniques, planning principles that take advantage of wind, solar and geothermal energy sources, as well as minimise the impact from these site-specific elements on the buildings. In some cases there are central systems to collect waste to convert to energy, water collection and reuse, smart grid technology only possible with large scale master planning, green roof technology and collective food farming and hydroponic food production systems. These cities average densities are 10 to 12 stories, though the range of building heights are from 4 to 60 stories, with the most dense structures occurring at the transit stops.
There has been much said about the sustainability, or lack thereof, of tall and supertall buildings. In our research we are attempting to put metrics to this typology as it relates to all other typologies and assign a common land mass to accommodate each typology, allowing for different densities to utilise the land in ways that support the density or improve the typology’s carbon performance through carbon sequestration on available unused parcels of land. An example is when we plan two 100- story towers on a 65-acre parcel, we only use 10 acres for the towers and the other 55 acres is available for planting prairie grasses, trees or food-producing plants that can breathe in carbon dioxide and produce oxygen, thus reducing the net carbon that the two buildings are emitting. Alternatively, if we put the same area that occupies the two buildings into single family homes spread out over the 65 acres, we know that the building coverage, road system and paving needed to support the “suburban” concept of density will reduce the area available for planting and thus reduce the amount of carbon sequestered in that density.
So far, we are finding that because the tall buildings have a lower net-to-gross area ratio than the lower density structures and the imbedded carbon of their respective construction materials, the difference in carbon emissions between high- and low-density environments cannot be overcome through carbon sequestration alone. Overall, we are finding that the three-to-four-story townhouse typologies are performing the best, considering the land coverage, the efficiency of space use and the simplicity of systems needed to construct and operate this building type. This typology has the minimum amount of embedded carbon while still leaving open space for carbon sequestration. It is also enough to offset the road system and underground services needed to access and service the units.
The difficulty with our findings is that the sample area and unit quantities are not necessarily dense enough to accommodate high speed rapid transit systems within walking distance. When we are talking of serving very large populations, there is a need to increase density to take advantage of supporting energy efficient transit systems within a short walk. The Chicago downtown Loop district is a good example of a dense compact core that can support several such regional systems. Its area is approximately one square mile and houses over 75 million square feet of space. It is walkable from one end to the other and is dense enough to have its own light rail system, subway system and regional system. Parking within the Loop is very limited and the core is beginning to change into a mixed use district with office, housing, educational and retail facilities all within the core. There is much work yet to do to reduce the carbon emissions of the older buildings which were built during the time of cheap energy and relatively inefficient mechanical systems, however there is a roadmap (Towards Zero Carbon: The Chicago De-Carbonization Plan, written by Adrian Smith + Gordon Gill Architecture and published by Images Publishing). This document has in large part been adopted by the city as part of its greening programme.
Each density, from tall to flat has their unique advantages and disadvantages when it comes to enhancing the standalone sustainability of each typology. The tall building can take advantage of stronger winds and cooler temperatures near the top for onsite energy generation by using integrated vertical axis wind turbines and in some cases integrate photovoltaic panels. In low buildings there is a greater roof surface area that is ideal for photovoltaic panels for power generation or green roofs for additional carbon sequestration. In addition each typology can take advantage of radiant heating and cooling, geothermal mining, natural ventilation, good access to natural daylight, low energy use fixtures and systems, low-flow water and water recovery systems to further reduce carbon emissions and increase sustainability.
In summary, tall is not the total answer for our future, nor is a low, spread out, low-density environment. Society needs a balance between the two so we can meet the needs of a growing population and at the same time reduce the effects that housing that population has on the earth’s limited resources. We need to harvest the renewable energy of wind, solar, hydro and geothermal energy that is part of the natural order on the planet to bring an increasing quality of life to our population—and we need to plan for this growth and transition from old, inefficient systems to new, less wasteful ones.
Practicing for over 40 years, Adrian Smith’s body of work includes some of the world’s most recognizable landmark structures. As one of the world’s foremost experts of supertall towers, he recently collaborated with Gordon Gill on the world’s first net Zero-Energy skyscraper. Adrian has also written two books pertaining to his work as an architect. They are Pro Architect 24: Adrian D. Smith and The Architecture of Adrian Smith, SOM: Toward a Sustainable Future. He is a Senior Fellow of the Design Futures Council.
This article is reproduced with permission from DesignIntelligence: http://www.di.net/articles/tall-global-and-sustainable/