Towers are difficult to justify environmentally, socially or economically, so why keep building them? asks Chris Twinn
The Observer/AJ Skyline campaign has raised many important questions about the place of tall buildings in London’s future and highlighted the potential consequences of the proposed 230 new towers in the pipeline. Yet to date little mention has been made of the complex sustainability issues related to tall buildings. Interdisciplinary think tank The Edge recently organised a debate at City Hall to tease out these concerns. While it is clear that the many new towers are an attractive vehicle for valuable foreign investment, this does not guarantee a sustainable approach for the London of tomorrow.
Some argue that foreign investors need glitzy high towers to attract their investment into the UK. The Barclays Skyscraper Index (2012) argued the very opposite: that a surfeit of tall buildings reflects a false concentration of capital and presages an economic downturn. A more likely scenario is that, when investors want their money back, the capital has been used up on high maintenance, servicing and costly refurbishment.
Towers – buildings above 20 storeys – are difficult to justify environmentally, socially or economically. They demand a disproportionate amount of natural and financial resource and are driven by pursuing capital appreciation rather than the creation of thriving, liveable neighbourhoods.
Towers inherently have poor net-to-gross and floor-to-wall ratios. In terms of embodied carbon, they require more structure and are an inefficient way to enclose space. They consume as much as twice the electricity and gas as similarly-sized mid or low-rise buildings. Their mechanical and electrical systems tend to be the most complex, relying on continuously operating high-capacity air conditioning behind sealed glass facades. In terms of maintenance, servicing and refurbishment, towers rely on lifts and relatively short-life cladding and glazing systems, which most likely bear no relation to lease cycles. Repeated bitter experience is proof that on-going maintenance costs often exceed a tower’s value, ultimately prompting premature demolition.
Towers must also work harder in terms of life cycle analysis to offset increased resource use
Today it is possible to design towers that will achieve the 80 per cent carbon reduction required by 2050 under the Climate Change Act 2008. Tall buildings have the inherent advantages of access to wind-driven ventilation and free cooling. Cross-ventilation can be effective at height if floor plates, core layouts and operable wind throttling windows are specifically designed with this in mind. Even the rigorous Passivhaus standard is viable at height.
Towers must also work harder in terms of life cycle analysis to offset increased resource use. Cladding should be designed for 100-year life and future-proofed for both change of use and climate change. Reliance on lifts can be reduced if the design encourages stair use both from ground and multiple sky lobbies. Financial stereotyping and ineffective planning policy stifle these types of innovation.
In floor area density terms, high-rise does not deliver any better than low and mid-rise. Just compare central Paris with Shanghai Pudong. China is now beginning to realise the perils of an urbanism of towers, requiring increased setbacks between tall building to allow penetration of sunlight to low level. Our higher latitude and lower sun altitude mean there is even less sunlight to penetrates canyon streets between tall buildings.
A few towers in select locations might be justified if they are of exceptional design quality. But planning policies must be updated to better match building form to housing needs, instead of the current policies that originate from a period when high rise equated commercial use. To ensure new developments meet real needs, council taxes should penalise unoccupied apartments.
Tall buildings as we are currently build them are not part of a sustainable future for London. In selected locations and for certain uses, they could be appropriate. But tower design needs to take a step change forward.
Chris Twinn is founding director of sustainability consultancy TwinnSustainabilityInnovation