Exploring the effects of urban pressure on ‘New or Renew’ buildings with CTBUH

Twice this year, I have had the opportunity to engage with peers around the world on the future of urban density and population at the Council of Tall Buildings and Urban Habitat (CTBUH) events. We have met people from across the world all tackling similar challenges on macro, micro and vertical scales. First was the Istanbul - Future Fit Cities CTBUH 2024 Europe Conference, then recently in London - New and Renew CTBUH 2024 International Conference. Some really critical issues around urban density for future growth and how to cope with disruption have been discussed at both. This makes it crucial to put in place appropriate planning to accommodate growing urban populations in ways that build resilience to both natural hazards and society-level threats such as unrest, economic downturns and shortages of appropriate and affordable housing.

Given predictions estimating a 60% increase in people shifting towards cities globally, understanding adaptive capacity becomes crucial. In the context of CTBUH, this often means increasing urban density to cope, with the consequence that building heights and the overall average verticality of cities increases. However, the challenge then arises; do we renew existing buildings and add floors to retain the embodied carbon of the existing structures, or must we construct entirely new buildings?

CTBUH’s data shows that the average height of the 100 tallest buildings in the world has grown from 344m to 410m over the last 10 years, and that in 2023 there were 57 cities building new structures over 200m tall. There is obviously an upwards trend, but does this mean that everything must be tall? What does this mean for urban density and the social challenges it may present? And then, what does it mean at the human scale in terms of the experience of being in the urban environment?

At the London conference, these issues were explored through the 400 presentations on themed topics. I have captured 5 key themes for me below:

Carbon currency

In a workshop I attended, ‘carbon currency’, engineers discussed tall buildings in Toronto, Chicago, London and Germany through the lens of embodied carbon and the need to account for it via either project costs or external carbon tax.

Through the projects I work on, I regularly advocate for an embodied carbon target of 500kg/m2 CO2, and in listening to the conference presentation and discussions, it became clear this target is becoming an internationally recognised benchmark.

In Vancouver, for example, it is emerging through the city planning process, in London the LETI (London Energy Transformation Initiative) targets are coming through planning conditions, however in Frankfurt better legislation is needed to achieve the goal. In Chicago and New York, materiality is the strategy for managing embodied carbon with the promotion of timber framed high-rise buildings.

My key takeaway from this session was that when planning delivers the goal of measuring or managing embodied carbon, positive change can be achieved.

Renewing cities

As many tall buildings are ageing, central business districts are also becoming more socially disconnected, as many tall buildings have not recovered occupancy levels post-covid or due to shifts in the local economy.

This concept provoked some intense discussions. For example, in responding to ageing and occupancy changes, the project and practice solutions have been about humanising tall buildings, reconnecting them with public spaces and simultaneously enhancing the urban fabric.

Projects evaluating 'working hours and working after hours' arise as an indicator to understand how people interact with buildings, and how context and amenities may help to make central business districts into ‘central social districts’.

Putting insight into practice

During a rapid-fire session that showcased project examples from around the world, common threads included social value challenges, planning constraints, the degree to which existing building fabric can be retained, and calculating the embodied carbon generated by retrofit. In some cases, project teams had measured the degree of recycling of materials for the local economy.

Every project also stressed the need for surveys and finding out as much as possible at the early stages. Across the board, everyone agreed saving tasks for later was not the answer! With retrofitting, existing buildings needed examining, especially as some of these buildings predate the age of BIM and good record keeping.

Vertical industry

Singapore and Lagos were cited as places where land use is being reconsidered, and as an alternative to industry spreading out over space, discussion focused on how urban sprawl can be contained by creating more density, stimulating the economy and ensuring urban places work better for people inhabiting the space. The consensus was that a solution is to build up and create vertical industries. This is particularly interesting for Lagos as it is a developing city, only just starting to grow tall, so has an opportunity to avoid the issue of sprawl from the outset.

Global North and Global South

The contrast between Singapore and Lagos is a good reminder that the Global North and Global South do enter the tall buildings discussion from different perspectives, which is important for us as practitioners to keep in mind.

Ultimately, we also have to challenge ourselves by asking, is dense high rise creating an appropriate quality of life for the people of a community? Is there a risk that building tall creates an isolated community where no one leaves the building? If so, planning conditions and policy need to shift to prioritise social outcomes. And sometimes, building tall may form the social perspective not be viable for some locations, communities or climate/geographic contexts.

Utopian ideas can be a thought-trap. For example, New York City is an icon, but is it a suitable approach for other places in the world?

Different perspectives also matter. In one presentation, a speaker explained how 31 cities across the African continent are starting to build tall and create modern central business districts, and how this is transforming the lives of people from informal (slum) settlements. However, in another talk this same trend was challenged on the basis that creating urban densities on a grid in these contexts may not have wellbeing and health as a central consideration, and that green spaces may not be adequately considered. This is an important reminder for us not to build without clarity of purpose.

Ultimately, as one attendee stated, “density needs identity”. As practitioners, we must spend time understanding context through data-led approaches. The projects we work on are not 'just projects'. They generate livelihoods, impact community behaviour and construct a legacy which the next generation of urban built environment professionals, and the coming generations of city-dwellers also, will inherit.