Circular building design: assessment of two versions of the same residential building highlights benefits of adaptable buildings

In the EU, 37% of all waste generated comes from construction and demolition. Worldwide, meanwhile, building construction and operation accounts for about a third of greenhouse gas (GHG) emissions and energy consumption¹. While the design of new European buildings has for some time placed an emphasis on energy efficiency during their use phase, quantifying the impacts of different types of materials used in their construction has gained attention in the last decade. For example, concrete and steel production are responsible for particularly high greenhouse gas emissions (among other impacts), and the refurbishment of existing buildings is thought to be more sustainable than demolishing and rebuilding them.

Extending the service life of buildings and closing material cycles are key ways of making them more circular, but most buildings in Europe are not designed to be adaptable and demolition waste is usually not re-used. Conversely, flexible designs allow for future adaptation – for example moveable inner walls and easily accessible installations (cables, water and heating pipes). Reversible designs, meanwhile, permit full recovery of components and materials – for example where joints are made with bolts and screws, as opposed to mortar and glue.

There has been little evaluation of the environmental benefits of these circular approaches, however. In a new study, researchers therefore compared the environmental impact of two versions of the same multi-storey residential building: one using a flexible, reversible design (planned to be built in real life) and one imagining the same structure with a less flexible design.

In the flexible design, the proposed building – an eight-storey block of 122 apartments – was based on a steel frame. The walls and floors were planned in a modular way, allowing for future restructuring of the internal space without major construction work. The design also followed other circular principles such as reversible installations and use of recycled and renewable materials. But the alternative design for the same building used an in-situ reinforced concrete load-bearing structure and screed flooring. Other components such as windows, flat rooves and facades were the same in both buildings – the main difference was the load-bearing structure.

To compare their impacts, the researchers carried out a whole building life cycle assessment (WBLCA) following the ISO (International Organization for Standardisation) 14040 LCA method, an overarching standard which includes all phases of LCA – construction, operation, maintenance and end-of-life phase. Impacts related to extraction of raw materials, direct land use, manufacturing of building materials and transportation were all considered. As one of the goals of reversible building design is better material recovery at end-of-life, the assessment also derived amounts of demolition waste recovered, recycled and sent to landfill (material flow analysis), assuming current waste treatment practices.

In terms of whole life cycle emissions, both buildings showed similar results for a life cycle of 60 years without major refurbishment: 13 (concrete) and 14.5 (flexible design) kg CO₂ equivalent per square metre, per operational year. The two designs also showed similar total impacts for most LCA categories, such as resource use, except for land use, where the concrete-based design significantly outperformed the flexible design (due to the latter’s use of wood), and conversely, the flexible design had about half the impact in terms of landfill waste at end-of-life.