The built environment is responsible for the extraction of virgin resources and represents a sizeable chunk of global CO2 emissions (approximately 39 per cent in total). This is true throughout all aspects of a building’s lifespan – be it during the construction, operational or demolition phase.

While considerable progress has been made in reducing the energy consumption of buildings, the focus must now be on the materials and processes involved, given that 11 per cent of a building’s emissions are related to materials and construction processes. On a global scale, the building industry consumes 40 per cent of all materials and generates 35 per cent of global waste. In the case of Denmark, the construction sector generates 1.2 million tonnes of concrete waste annually, as well as 158,00 tonnes of wood residues and 5,000 tonnes of plastic waste1. Finding ways to reduce waste in the demolition phase and keep scarce resources circulating for as long as possible is therefore essential.

For architects, who seek to design buildings that are aesthetically pleasing and will last for generations, the challenge they face is how to design so that if even if buildings are dismantled, the materials involved can be recycled or reused, thereby maximising their lifespan and reusability. In essence, what we are referring to is the need for a circular approach to construction and design.

Historically, the not-for-profit housing sector in Denmark has incorporated societal and social responsibility into the design of its dwellings. Now, the sector is seeking to revolutionise social housing in the country by creating projects constructed according to circular principles.

To this end, the Circle House project was established in 2017. Consisting of 60 social housing units, Circle House is located in the Lisbjerg Hill district – a development zone focused on sustainability in the north of Aarhus, Denmark’s second largest city. With a mixture of two and three storey terrace houses and five storey apartment blocks, the project will have a building density of between 65 – 80 per cent. Construction is expected to be completed by mid 2023.

Consisting of over 60 partners gathered from across the entire building value chain in Denmark, and open to anyone who wishes to participate, the project aims to develop and disseminate knowledge about circular construction across the industry and across silos. Circle House is devised as a lighthouse project that can function as a blueprint for the entire construction industry in Denmark, as well as decision makers, on how it to build according to circular principles in a manner that is not only feasible, but also sustainable and profitable. This means that Circle House is being tendered on market terms, with assistance from the Danish Environmental Protection Agency’s Environmental Technology Development and Demonstration Program (MUDP) and Realdania’s Innovation Program in Construction.

Circular construction is a relatively uncharted area and will require legislative amendments and new actors in the construction value chain to flourish. For the Circle House project, this means the development of circular tender documents, defining circular construction criteria, and new building standards. Currently, there exists an insufficient market for to purchasing used building materials, including valuing and labelling them in accordance with current Danish legislation. It is also difficult to estimate the potential for selling used building materials in 50 years.

The project’s concrete objective is that 90 per cent of the project’s materials can be demounted and reused or resold without loss of value – so-called ‘design for disassembly’.  To achieve this aim, the buildings have been designed to allow for them to be dismantled and the structural components can be reused with minimal loss of value.

A key aspect of the project has been understanding how to design in a circular manner using concrete, given that valuable knowledge already exists on how to create circular buildings constructed of timber. Therefore, the ambition is that the buildings will consist of a minimal amount of different, demountable elements, where there are six in total: two different wall elements, two different beam lengths and two deck lengths. Furthermore, while cement is the material of choice, its use is minimised as much as possible in order to lessen the project’s CO2 footprint. For example, the demonstrator and mock-up of the building system shows a façade of the buildings constructed from cork and old newspapers, while eelgrass and granules have been used to provide the building’s insulation. The flooring’s underlay is made of used car tyres. Furthermore, lightweight facades have been used that can be demounted and reused again.

Architecturally, the building will be different in the sense that the buildings’ interiors, including structures, connections, and installations, will be visible on the exterior. By making the interiors part of the building’s aesthetic features, residents or the housing association will easily be able to change the size of the dwellings without having to demolish the building.

A prototype of Circular House is on display at the project’s property developer, Lejerbo’s offices in Valby, Copenhagen.  All of the building’s layers, materials and products are exposed, displayed and described, and the space is currently used as an inspirational meeting and event space.

Once completed, Circular House will be the world’s first social housing project constructed according to circular principles. In addition to serving as housing, Circle House is a scalable demonstration project that can provide the construction industry with valuable new knowledge about the experience of circular building, including how to construct circular buildings based on market terms, as well as which resource savings, reduction in operating costs and profits can be generated.  Furthermore, given that the social housing accounts for one-fifth of all residences in Denmark, the sector can play a leading role in stimulating demand for circular residences.

The hope is that Circle Housing’s tenants will realise that housing designed according to circular principles also results in housing of a higher standard. Furthermore, the fact that the project will be inhabited by residents will allow for valuable learnings to be gathered about how circular buildings function in daily life.

On a wider level, circular construction will help reduce the build environment’s carbon footprint. The Ellen Macarthur Foundation has estimated that a circular approach to building will reduce CO2 emissions from materials used in the built environment by 38 per cent by 2050. Furthermore, in the case of Denmark, the foundation estimates that the total economic potential for Denmark in implementing a circular economy in its building industry amounts to approximately € 7.75 billion per annum up to 20352.