The situation is paradoxical. While prices for construction materials are rising – since May 2021, reinforced steel mesh and timber have gone up by over 80 percent and almost 35 percent respectively, for example – and raw materials like sand and gravel are in increasingly short supply due to the global construction boom, the mountains of construction waste continue to grow. The construction sector is the biggest waste generator in Germany, producing some 230 million tonnes a year. On top of that, it is responsible for 40 percent of the country’s CO₂ emissions. Making systematic use of the potential for recycling construction waste and components would save valuable resources and reduce greenhouse gases. 

Construction materials from waste failing to gain traction in building sector

Take concrete as an example. A pilot project in 2013 as part of tenders put out by the Berlin Senate Administration to build a research building at Humboldt University found that the use of recycled concrete could reduce CO₂ emissions by 7 percent compared with conventionally produced concrete. In addition, 66 percent less energy is required for production and transportation. 

Recycled concrete has nevertheless failed to gain traction in the building sector. Of the approximately 74 million tonnes of mineral waste generated from construction waste and road rubble in 2018, around 60 million tonnes were recycled, but the recovered materials were primarily used in road building, earthworks and landfill construction, i.e. relatively low-value activities. “We can actually put a monetary figure on the loss in value – a tonne of concrete costs up to €130, while a tonne of recycled construction material costs just €8 to €10,” says architect Anja Rosen, Honorary Professor of Circular Construction at the University of Wuppertal. 

EU taxonomy calls for high-quality processing and reuse

The EU Taxonomy Regulation, which defines sustainability requirements for economic activities and investments, is likely to spell the end of such downcycling. Among other things, Article 13 requires high-quality processing and reuse of materials and calls for the reduction and avoidance of waste when constructing and demolishing buildings. 

A real-world test will come in autumn 2022 for listed residential developer Instone Real Estate while working on part of the Friedenauer Höhe scheme in Berlin – a joint venture together with developer OFB Projektentwicklung. While complying with all relevant standards, ceiling construction will see the first ever use of recycled concrete produced by Swiss startup Neustark, which is based on a climate-friendly core method that conserves resources. The new concrete recipe reduces the proportion of cement, which results in CO₂ emissions that are 20 percent lower than for conventional concrete. “On completion of the pilot project, we will continue to consider what future applications make sense and where the technical and planning conditions are right,” says an Instone Real Estate spokesperson.

Disposal and reuse of insulation boards is likewise going green. A first demonstration facility commenced operation in the Netherlands in June 2021 that enables HBCD flame retardant – which is harmful to the climate and the environment – and other additives to be removed and the polystyrene recovered. Previously, under the EU’s REACH chemical regulation this material could only be sent for thermal recovery. Burning it not only destroys valuable resources, it also releases large quantities of CO₂. The Polystyreneloop consortium, which includes EPS producer BASF and insulation systems manufacturer Rygol, is currently working on a closed-loop system for recycling waste from polystyrene insulation materials. The aim is to recycle 3,000 tonnes of HBCD material every year. Since 200,000 tonnes of such waste arises in Europe annually through demolition and refurbishment, the potential is significant.

Entering new territory means greater planning effort

Proof of the fact that deploying used materials is architecturally appealing comes courtesy of the single-family dwelling constructed by Gundlach Bau und Immobilien in Hanover, based on ideas from architects Cityförster. More than 50 percent of the construction elements used across the building’s 150 square metres of living space have been reincarnated. The wooden façade includes discarded sauna benches, while the staircase features oak beams from half-timbered buildings. The inbuilt furniture is made of repurposed trade show stands; bottle caps from the hospitality industry were used to create wall mosaics in the bathroom. All the building services are new, as is anything where building regulations left no choice. “The whole project was very experimental,” says Gundlach manager Franz-Josef Gerbens. 

Normally plans are drawn up first and then the materials bought in. “Here, the architect had to plan the house around the windows, for example, which required extra creativity.” The partners entered new territory when it came to the issue of who provides a warranty for the used products, because building a recycled house is not covered by legislation. It was thus essential to create trust with the tradespeople involved. “Fortunately, the authorities played ball, which is not usually the case.” The company spent three years on preparations and the build lasted 15 months at a cost of about 10 percent more than “normal”. 

The ecological potential of recycled materials is there to be explored. For builds to make economic sense, the construction and real estate sector needs to switch its processes for planning and building, operation, deconstruction and comprehensive documentation throughout the lifecycle to a circular value-added approach. 

It is also important to set up materials marketplaces that create transparency into supply and demand. In addition, investors, developers and portfolio managers need to be open to specifying corresponding products so that recycling gathers pace in the construction sector. Otherwise it will not be possible to reconcile protecting the climate with acceptable costs and high resource productivity.

By Dagmar Hotze