Buildings stand at the epicentre of the climate change and sustainability debate, as discussions at the recent COP26 conference demonstrated.

Buildings are responsible for forty per cent of our energy consumption and more than a third of greenhouse gas emissions.

Meanwhile, construction and demolition waste is the most voluminous waste stream in the European Union, accounting for more than a third of all waste generated.

Unsurprisingly, therefore, innovations focusing on reducing carbon emissions from buildings throughout their lifetime are among those currently most highly prized by authorities across Europe.

This is literally the case with Erden, a company in Feldkirch, Austria, which won first prize in the inaugural New European Bauhaus awards in the category for materials, techniques and processes.

Erden means earthen in German, and it’s simple, unadorned rammed earth that the company uses to create the building blocks of the future. Erden’s earth typically comes from excavations made by construction projects: if the company didn’t take the earth, it would go to landfill.

“This is the most ecologically friendly solution imaginable for building, because we’re using earth that would otherwise be thrown away,” says Sami Akkach, an architect at the firm.

Akkach says the prefabrication method for rammed earth that won the NEB prize means the blocks can be transported to and put together on a building site “like Lego”, because rammed earth enjoys similar properties to bricks and concrete.

Experts check the earth for composition and building suitability, and if satisfactory it is sieved to remove the largest particles. Technicians then verify moisture content, compressive strength and erosion resistance to ensure durability and reliability.

During the prefabrication process, loose earth is poured into a mould and compacted in layers of roughly 10 cm. Depending on the thickness required, rammed earth blocks usually need 4-6 weeks of drying time, after which they can be moved and loaded safely to a building site.

“And for interiors, visually it’s a highly attractive material, because earth contains a diversity of rich colour tones and textures” he adds.

Rammed earth, which has high thermal mass and therefore keeps the internal temperature of a building relatively stable, is one of many materials that can contribute both to climate resilience and energy efficiency.

Seeing waste – such as earth at construction sites - as a resource, and thereby embedding a circular-economy approach in the construction industry, is an important start in focusing the industry’s attention on sustainability.

HOUSEFUL, an EU-funded project developing a suite of solutions for circularity in buildings and construction processes, is also helping to source eco-friendly materials for construction and renovation.

The project is trialling a model of a local database containing dozens of reusable, recycled and renewable construction materials.

The database will help builders identify sources, assess circularity potential and provide information about the supplies’ quality and origin – and earth for ramming could well feature extensively in such databases.

Another innovation is 3D building information modelling, which will share data about every aspect of a building’s design and construction across the value chain, together with a materials passport that will document precisely a building’s composition.

Combined with a detailed guide for managing waste streams from demolished and refurbished structures, these solutions are intended to maximise circularity and minimise waste throughout the value chain.

On the other side of Austria from Feldkirch, architect Georg Reinberg, a pioneer of ecological building design and solar architecture, is working on holistic approaches to challenges facing the built environment.

Reinberg’s work graces the Cambium Community Project, a HOUSEFUL demonstration site and a former military barracks in Styria province, south-west of Vienna, that has become a living and working space for 70 people, who are creating an eco-village with minimal environmental impact.

“I designed a greenhouse for growing vegetables, and the glass for the structure was taken from a demolished office block,” Reinberg says.

“Construction materials ready for reuse are in abundance all around us, and helping builders to identify sources, waste streams and quality standards locally could have a transformational effect on the sector’s environmental impact.”

But the project’s rationale is that buildings need to reflect climate-neutral values not only in how they are constructed, but in how they are used and lived in.

“The blackwater from the site is cleaned and used in the winter garden. Elsewhere in the project, organic solid waste is converted into biogas and fertiliser respectively. It’s the circular economy in action for a new kind of living,” says Reinberg.

So will Europe’s future homes in the net-zero era be made of rammed earth, a material that was ubiquitous centuries ago in Europe’s built environment?

Dara Turnbull from advocacy organisation Housing Europe, another HOUSEFUL partner, sees such innovations as essential to greening this sector.

“We need to recognise that the use of ‘virgin’ materials, such as concrete or steel, is not sustainable at the current rate. These are finite resources, and we need to treat them as such,” he says.

“Designing and renovating buildings along circular principles is the way forward. Public, cooperative and social housing is already taking a leading role on this in many countries, with a number of exciting frontrunner circular housing projects underway.”

If Europe’s cities are going to become truly sustainable, and if global emissions reduction targets are to be met, the construction sector will have to have to find new ways to source materials, and new materials to source.

Rammed earth is just one of many circularity options that are steadily moving our built environment towards climate-neutral sustainability.

A highly polluting sector like this has a long way to go, but that also means the improvements and changes it pioneers could have an unparalleled positive effect on emissions and climate resilience in the coming decades.