Author: Satu Huuhka
When we strive towards more sustainable cities, we almost automatically direct our focus on new buildings. We forget the fact that the overwhelming majority of our future cities already exist because buildings are such long-lasting assets. Luckily, they are also adaptable ones.
Why existing stocks matter
Most European countries and cities have accumulated their building stocks over the course of their history. As a result, their building stocks are what researchers call ‘mature’, that is, stocks that renew very slowly, less than 1 % annually . At such a pace, it will take at least a hundred years, if not several hundred years, for new construction to replace the stock of buildings that currently exists in our cities . The logical, sustainable approach is to focus on building upon the buildings that we already have.
Why not build new?
‘Why shouldn’t we focus on increasing new construction?’, one might ask. In addition to lacking the supply of skilled workforce necessary for doing that, such a strategy would be highly detrimental for our planet. From actually monitoring the energy uptake of both new and old buildings, contrary to what we first thought, we have learned that old buildings typically perform better and new buildings perform worse . What’s more, we are increasingly aware of the energy and emissions ‘embedded’ in construction materials, which worsens the environmental performance of new buildings . Taking all of this into account, it is clear that replacing of existing buildings with new ones is definitely not a viable option nor a solution for climate change mitigation.
Building conservation is circular economy at its best
At its core, circular economy is about life cycle extension through reuse, repair, and repurposing . When it comes to buildings, though, the idea is still surprisingly controversial. The importance of historic building preservation is generally no longer contested in our societies, but no consensus exists for the more modern ones. Post-war buildings tend not to be old, beautiful or rare enough to be valued as heritage buildings. Yet, they are quantitatively substantial and made from highly carbon-intensive materials – a carbon investment that is wasted when they are prematurely replaced. Therefore, taking a resource-efficient, conservationist approach to our modern building stock will have significant positive impacts on the efforts being made to decarbonize our cities. Luckily, in addition to being long-lasting assets, existing buildings can also be much more adaptable than one might think .
What we know – and what we don’t know
There is a special field of research dedicated to looking into the potentials and dynamics of building stocks . From this research, we already know that the life expectancy for modern buildings is much shorter than for historic buildings , despite the fact that in engineering terms, modern buildings are usually deemed as structurally more robust than older buildings. We also know that technical concerns such as deficiencies are not the main drivers for demolition, even if that is what our instinct misleadingly tells us . Indeed, research has found that the leading drivers are what the building is being used for and its tenancy. Industrial, commercial and public buildings have much higher demolition rates to residential buildings and are demolished after a much shorter life span than homes . These findings suggest that to promote life cycle extension, instead of taking a replacement driven approach to buildings in our cities, we should focus on adaptation. Especially for non-residential buildings, considering how they can be kept in use for longer, thus extending the building’s life cycle and making further use of its valuable resources.
Undoubtedly, there is still so much that we do not know when it comes to the drivers for building demolition, transformation, and replacement. In order to develop knowledge-based sustainable urban development policies in our cities, we need to keep sharing research and knowledge. Given the aim to limit global warming to 1.5 degrees by 2040, there is neither time to lose nor room for overlooking the value of our existing building stock.
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