Designing buildings to cope with extreme climate events: Part 1
The planet is becoming evermore hostile to human life – how can building design help us to adapt? Today: high winds, high waters.
Rapid urbanisation means billions more people are living and working in cities – mostly in skyscrapers. That may be bad news for the planet. Typically, the taller the building, the less energy efficient it is. So, how will we build the greener tall buildings of the future?
19 June 2020
According to the UN, in 2007, when the world’s population was approaching 6.7 billion, the number of people living in urban areas was approximately equal to the number living elsewhere. However, by 2050, when the global population is predicted to have reached 9.8 billion, twice as many people will live in urban areas than elsewhere. If you’re wondering where an additional 3 billion-plus people will live and work: look skyward.
Advances in construction methods and materials, alongside unmanageable traffic congestion and a resurgence in city centre living have seen a growth in the construction of tall buildings. Figures from the Council on Tall Buildings and Urban Habitat (CTBUH) show that the number of buildings over 150m high has increased from 2,376 to 4,991 in the past 10 years. Among buildings taller than 300m, numbers have increased from 542 to 1,616.
But the ever-increasing number of people living and working in cities, and the construction of the buildings that will facilitate it, could be very bad news for the planet, as early research indicates that tall buildings are proportionately more energy intensive than short ones.
A 2017 study of 600 British office buildings by a team at University College London (UCL) showed that as a building’s height increases from five to 20 storeys, carbon emissions from energy use, per unit of floor area, double.
Taller buildings are subject to forces that smaller buildings aren’t. “[They] rise above their neighbours and are exposed to stronger winds, lower temperatures, and more direct sunshine,” explains Philip Steadman, Emeritus Professor of Urban Studies and Built Form Studies at the Bartlett School of Architecture, who led the research. “[So] they need more heating in winter and more cooling in summer.”
A 2017 study of 600 British office buildings by a team at University College London showed that as a building’s height increases from five to 20 storeys, carbon emissions from energy use, per unit of floor area, double.
There is a scarcity of studies about the carbon impact of running tall buildings. One of the reasons for that is operators are notoriously guarded about releasing the necessary data, for fear they might give away their competitive edge. The data from private building operators that was used in the UCL study, for example, was provided on strict condition that no individual building data would be published.
Another reason is the current primacy of computer modelling to determine buildings’ energy consumption, which according to Professor Steadman has consistently suggested that tall buildings are as, or more, efficient to run – results that are unsurprisingly favoured by those with financial interests in building tall buildings.
Steadman claims that a powerful lobby for computer simulation models is still reluctant to accept the results of his research. “I have given a number of talks [about the research] that are well attended by planners, but not developers. And where I encounter them [developers] they are much harder to convince,” he says.
Despite this reluctance to accept Steadman’s results, comparable evidence has been available for a while. As long ago as 2004, a study of 20 government office buildings in Hong Kong measured each building’s height and the energy used from functions such as air-conditioning, lighting and lift operations. However, despite gathering all the necessary information, the study’s analysis was focused elsewhere. “There was enough data to draw comparable conclusions to our research, but the paper did not,” says Steadman.
High rise buildings and high density cities
High-rise buildings are commonly seen as providing the means of achieving sustainable density in high-population urban areas. Skyscrapers can accommodate large numbers of people within relatively small ground level footprints, enabling cities to leverage the benefits of proximity and avoid sprawl. Nonetheless, it is said that such “vertical villages” limit human interaction, inhibit creativity and innovation, and cast both a literal and figurative shadow over the urban realm. So, is building upwards really the best means of managing increasingly densely populated cities?
At the heart of tall buildings’ energy inefficiency is their use of glass, whose high conductivity heats the building in summer and cools it in winter. Steadman’s research found that the proportion of a building’s exterior that was glazed “increases systematically with [a building’s] height, increasing heat loss and heat gain”.
Most of the world’s tallest buildings are fully or nearly fully glazed, according to Simon Sturgis founder of Targeting Zero, a sustainability consultancy in London. And the problem with glass isn’t limited to its thermal inefficiency – maintenance of glass buildings is relatively wasteful, too. To reduce the amount of air-conditioning needed to cool the interior of a mostly glass building, they are typically built with a triple-glazed façade with a large gap between the outer pane and double-glazed inner panes, in which electronically operated blinds fit. There is also the laminate required for strengthening, and then a heavy aluminium framing system to support the five sheets of glass.
Furthermore, these glazing units don’t last as long as the traditional stone-and-steel façades of older skyscrapers. Sturgis estimates that they must be replaced every 30 to 40 years compared with every 100 years for a building with exterior glazing of 40% – a figure that reflects that of Empire State Building-era skyscrapers – and one that he suggests should be a target for future buildings.
A further issue with fully glazed facades is that they come in large units, meaning that a fault in one section often requires a wholesale replacement. “And the material is hard to recycle, so there is a huge resource impact,” adds Sturgis.
It seems clear that if the fast-urbanising world cannot curb its appetite for tall buildings, it will need to start building them with less glass.