The best materials to build sustainable cities

Building materials are an issue because 70% of global greenhouse gas emissions come from cities¹ and 38% of energy-related emissions come from the construction sector².  In her 2020 State of the Union address, EU President, Ursula von der Leyen said “they need to become less wasteful, less expensive and more sustainable,”

But von der Leyen also pointed to a future direction. “We know that the construction sector can even be turned from a carbon source into a carbon sink, if organic building materials like wood and smart technologies like AI are applied.”

Where’s the roadmap?

But is it that simple? Do we just transition to wood and use some smart-tech to reduce emissions?

“There is no manual on this,” says Sabina Leopa, deputy director at Urbasofia, a town and regional planning company that supports several EU urban development projects. Leopa is also working with Build-in-Wood, a European funded Horizon 2020 project with the goal of goal of making timber the standard construction material for multi-storey buildings.

“When it comes to something like sustainable mobility, we have initiatives and guides and climate adaptation plans. But when it comes to decarbonising our buildings, cities are asking how to do it and there’s nothing available for them yet.”

Leopa is optimistic however that guides can be created despite the complexity of the task. She believes that overarching guidelines are needed that are easy to understand. For Leopa, choosing renewable materials is one of those guidelines.

“The question isn’t really when wood is the right material,” says Leopa. “There are no technical barriers to using wood anymore. You can build an 85-metre tower out of wood today. Wood is basically always the right material. It’s bio-based, it’s renewable. It’s ticking all the boxes for what people want to live in.” 

Creating the guidelines

Some guidelines appear to be on the way and they are coming in various forms. In Germany, Professor Dr. Annette Hafner and her team from the Chair for Resource-Efficient Buildings based at Ruhr-University in Bochum, Germany are developing a tool that helps municipalities estimate how much greenhouse gases they would save if they increased the proportion of wooden houses in their area. It provides a detailed digital plan of all the buildings in a municipality and then looks at the best way to optimise each building from a climate-perspective. This includes looking at the type of building, the age of the building and whether renovation is required or not. In this way, a city will know where and when to build and with what materials.

These kind of tools will be key for cities and towns to make the sustainable shift to renewable materials. But what about other traditional materials? 

“They are making progress in concrete and steel and this is positive to see,” says Sabina Leopa referring to new innovations to reduce the emissions from both materials.

“These materials can be recovered and re-used also, which is good, but re-using them also requires energy and this is something that is not always part of the discussion today. We talk a lot about operational emissions but not about embodied emissions.”

Operational emissions are the emissions used in heating, cooling and running a building. Embodied emissions include the emissions from sourcing the raw material, manufacturing the components and everything involved in the actual construction.

And this is where wood and bio-based materials provide a strong advantage.  They are renewable, store carbon and the production process has relatively low emissions.

Paving the way for a transition to wood

“If we want to simplify things - and we probably have to in order to move everyone in the right direction - then we should always be choosing wood and always from sustainably managed forests,” says Leopa.

But there are challenges with this also. A fast transition to wood construction could cause problems for the entire construction industry.

“We have to lay the groundwork for a shift in the industry. We need to make the transformation and move people from traditional construction to biobased construction in a manageable way. Having a proper strategy in place will be foremost for a quick transition,” says Leopa. 

But if we make the shift, then Leopa believes considerable gains can be made. The next step will be ensuring that components from existing buildings can be re-used in future buildings. Cities are constantly changing and adapting and its buildings will need to do the same.  Standardising components is a potential solution.

Re-use of building parts

“Think of it as a lego game,” says Leopa. “You have a lot of parts in the box for one project but then you can re-use those parts and make something else later on. This won’t dent creativity but rather allow for flexibility to build something new with the same parts instead of sourcing a large amount of new resources,” she adds.

Leopa’s organisation, Urbasofia, believes this can be done. Urbasofia works closely with the EU on many projects and has seen the enormous positive effect it can have if the EU sets guidelines and even regulations.

“If the EU sets up objectives and financing, then governments and cities will make quite sure to comply with that,” says Leopa.

While the future looks wooden, it’s also clear that the transformation needs to be managed. If done well, emissions from buildings could be drastically cut and help mitigate climate change in line with the UN’s 1.5 degree climate goal. The race is on.

Stora Enso is a member of the project consortium of Build-in-Wood, a European Horizon 2020 project improving the sustainability of European construction.