Antony Wood, Executive Director, Council on Tall Buildings and Urban Habitat
The vertical city is increasingly seen as the most viable solution for creating more sustainable urban centers, especially in developing countries such as China or India where population growth and urbanization is at its most pronounced. However, the full implications of concentrating more people on smaller plots of land by building vertically need to be better researched and understood.
Image: Adrian Smith and Gordon Gill
On the one hand there are many energy benefits from building tall. Growing taller and denser versus horizontal spread offers distinct advantages for urban infrastructure systems. Efficiently-designed tall buildings utilize less materials for enclosure per unit of usable floor space, a smaller surface area for heat loss/gain, a natural energy share between floors and provide the potential for harvesting solar and wind energy at height.
On the other hand there are disadvantages with building tall that offset, and may even negate, the benefits of concentrating people together in taller buildings. Smaller floor areas may limit people’s access to natural light, views and ventilation. Growing taller requires more materials and primary structural systems, which may affect the overall sustainability equation. The general concept of ‘vertical’ being more sustainable than ‘horizontal’ may be true, especially when the larger-scale urban scenario is considered, but the myriad factors that contribute to this scenario should be better investigated.
During the CTBUH 9th World Congress in Shanghai, 19-21 September, the Council will formally release its latest technical guide, Natural Ventilation in High-Rise Office Buildings, part of a series of CTBUH publications that analyze various aspects of tall building performance. Heating, ventilation and air conditioning (HVAC) in tall buildings typically account for 33 percent or more of overall tall building energy consumption, according to U.S. Department of Energy data. More than half the HVAC energy use in a tall building is the result of efforts to reduce heat gain, lighting, miscellaneous power use, and systems to counter solar and thermal fluctuations. It could be argued that the increased efficiency – or elimination – of these systems is the most important single step in making tall buildings more sustainable.
This type of research is essential to the future of tall buildings and cities. Building owners, developers and consultants need to understand the ‘sustainability threshold’ for height – that height or floor count beyond which additional height would not make sense on sustainable grounds. This will never be an exact science and will differ not only from city to city, but from site to site and building to building. It is, however, a measure of extreme importance – and one which the global building industry needs to urgently strive toward.