What can London learn about tall buildings – particularly on sustainability – from the birthplace of the phenomenon, Chicago?
and live link-up between the two cities last week sought to find out, in the aftermath of the publication of NLA’s tall buildings survey
for 2021 last week. And a ‘creative’ drive toward getting better construction materials with less embodied carbon along with more mixed use are major parts of the push required.
Lynn J Osmond, president and CEO of Chicago Architecture Center kicked off the debate with an overview of the city and its ‘lengthy love affair with tall buildings’, some of which rise to 110 storeys. One of the pursuits of the ‘hub and spoke’ city has always been ‘to get more people living downtown’, said Osmond, pointing to the advent of Millennium Park changing the dynamic of the city and allowing more residential.
Chris Drew of Adrian Smith + Gordon Gill Architecture said Chicago had been a leader on decarbonisation back in 2008, with an early action plan to reduce the footprint by 25% by 2020 and 80% by 2050. That led Drew’s practice to take a ‘deeper dive’ to try and do better and achieve carbon neutral by 2030. This was partly through a look at utilities infrastructure to support the changing demand of a city in transition and using parametric modelling to assess how retrofitting buildings would impact the whole landscape of emissions.
‘One of the lessons you learn from retrofitting buildings is the considerations that you want to make in new buildings’, said Drew. It also looked at the relationship between density and carbon, analysing 2000 living units from across all typologies. The study found that, over 40 years, the lower rise communities would have lower lifecycle emissions, said Drew, and in all cases embodied carbon made up 10-20% of that.
But to stop a ‘tsunami of carbon emissions’ that happens with new buildings during construction, materials like concrete should be assessed and improved.
‘We have the tools and technology to reduce the embodied carbon of concrete by at least 75% or more’, he said, if industry tried harder.
The embodied carbon of steel and aluminium, too, could be reduced, with a total possible reduction across those three main materials of some 56%. ‘That’s pretty impressive’, said Drew. ‘Our grid is definitely getting cleaner, and the materials we use need to become better’.
Allies and Morrison partner Jo Bacon talked about the challenges in London, saying that Londoners were ‘a pretty divided bunch’ on tall buildings and densification. The new London Plan has applied a six-storey threshold, albeit allowing each borough to define the definition of tall. ‘There’s a huge need for different boroughs to collaborate’, she said, pointing too to the new draft design code that says tall buildings are only appropriate in city centres. Some 90% of London’s tall buildings are residential, and thus could be the ‘solution’ to the capital’s housing problems. But London is not as adventurous as Chicago in terms of producing mixed use buildings, she said. ‘Our ownership structures are too tough to make this viable’.
Identifying zones suitable for tall buildings, however, often makes them the ‘go-to solution’ in that area, she added. The New London Plan will require boroughs to ‘really robustly assess character’, Bacon suggesting that there is an appetite for a more context-led approach to towers in other cities as well as the practice is showing at an ‘urban ensemble’ it is designing at Humber Bay Shores in Toronto.
Other panellists included Cynthia Roubik, assistant commissioner at the department of planning and development at the City of Chicago and WilkinsonEyre’s Dominic Bettison. The former spoke about the benefits tall buildings can drive at neighbourhood level, with the city expanding its downtown zoning, developing a new ‘Neighbourhood Opportunity Bonus’, with money raised going into a fund for local projects and improvements.
Bettison, meanwhile, argued that tall buildings can contribute to the zero carbon city agenda, offering positives on sustainability targets as part of a mix of other strategies, densification rather than urban sprawl and requiring efficient use of land. But tall buildings use more energy in pumping and lifting in construction, operation, and demolition, with perhaps 150% greater embodied energy costs.
‘Better certification and supply chain information is needed by us as designers and owners which will really allow us to appropriately select components, systems and design elements of the building’, he said.
By the same token, however, they could potentially help deliver the 15-minute city, he said, even if that requires high rise buildings to be mixed use and for green and amenity space to be delivered as part of their design. They should also be designed for ‘long life, loose fit’ to allow them to be refurbished ‘over and over again’.
Osmond had the final word on tall buildings, from Chicago. ‘We here have all drunk the Kool-Aid; however, we know the challenges that lie ahead’. We have ‘an architecture of emergency’, to create net zero buildings if we want to meet the Paris Climate Change goals, she added.
‘It’s really a global conversation and only through conversations and sharing best practices that we can really meet that target’.