Luke Askwith of Gensler reflects on our recent debate on the feasibility of tall buildings being net zero, as we hear for and against the sustainability of high rises.

The climate crisis is forcing us to ask hard questions about our built environment. As we gathered in the London Centre, the New London Model showed a city defined by clusters of tall buildings around key transport nodes – but can these tall buildings be sustainable? Jo Bacon, Architect and Partner at Allies and Morrison, chaired this debate, starting by asking the audience their opinion. In answer to the question ‘Can tall buildings be sustainable?’, 67% of the audience voted in favour, 33% against. 

 

Russel Whitehead, Director and Building Structures Division Lead at Robert Bird Group, kicked off the debate with a simple question: with a growing population, we need to build more – the question is, where? He argued that dense developments around infrastructure are the most sustainable way to plan our cities, and tall buildings enable open space and other positive contributions to the city, whilst also playing a key role in defining its character. Russel outlined how the larger scale of tall buildings is a key factor in improving their efficiency – and we can make huge improvements by making best use of materials, including reusing steel where possible. 

 

Simon Erridge, Architect and Director at Bennetts Associates, began by outlining the importance of embodied carbon – he argued that this should be our number one priority since these carbon emissions are immediate and can be the equivalent of more than 20 years of a building’s operational carbon. He then outlined the ‘carbon premium’ of a tall building, laying out how tall buildings will always have increased embodied carbon compared to low rise buildings. Simon outlined some ways this ‘carbon premium’ can be mitigated, but all of these techniques are also applicable to low rise buildings. Therefore, no matter how sustainably they are designed, tall buildings will always have an inherent ‘carbon premium’ that comes with height. 

 

Luke Askwith, Architect and Senior Associate at Gensler, outlined how tall buildings have efficiencies that mean they typically use less energy for heating and operation than comparable low-rise buildings. In particular, mixed-use tall buildings that can share energy between uses can perform far better than any other building type if well designed. Luke described the potential for tall buildings to have increased lifespan compared to low rise equivalents; the intrinsic planning and financial value incorporated in a tall building means it’s much more likely to be repurposed or repositioned at the end of its life, and we’re seeing that on many current projects. This also means it’s essential to make a longer term plan with any tall building. 

 

Agnieszka Zimnicka, Regeneration Manager – Place at London Borough of Tower Hamlets, began by outlining how tall buildings rarely contribute significant green space to the city, and tall buildings create microclimates that can make it harder for vegetation to grow. Potential for renewable energy generation in tall buildings is limited, and the impacts of tall buildings through the shadows they cast and the heat island effect can increase the energy required for heating or lighting in surrounding buildings, and reduce their potential for renewable energy generation. Agnieszka then outlined how the transient nature of tall building occupants means that these communities do not develop the same sense of belonging and community that are more prevalent in other building types. 

 

The panel then answered a series of questions from the audience, covering issues ranging from developing a new exemplar carbon standard for tall buildings, the impact of tall buildings on London’s character, and whether it is possible to build a net zero tall building without offsetting. 

Another poll was taken at the end of the debate showing 59% of the audience now thought that tall buildings could be sustainable vs. 41% who thought they couldn’t. Clearly tall buildings face some challenges with the balance tipping slightly in favour of tall buildings not being sustainable, but the majority of those in the audience were still of the opinion that, if well designed and constructed, tall buildings can be sustainable.