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.

The researchers note that when longer building lifetimes are considered, impact per year decreases significantly, especially since the construction phase makes a high contribution to the overall impact. GHG emissions related to the construction phase decrease by 40% when a lifetime of 100 years is considered. Therefore, a flexible building with an extendable life may really ‘pay off’ if the design serves to extend the life of a building, or when materials are recovered for use in another building – direct re-use of the foundations, wooden ceiling and steel structure could save 14% of building GHG emissions.

Indeed, the flexible design permits a higher rate of closed-loop recycling, notably of steel. Downcycling of recovered concrete, which would be available when the concrete-based building is demolished, offers fewer advantages in terms of material re-use. The Swiss researchers  found no established recycling market in their home country for materials such as gypsum or mineral wool, though these may be developed elsewhere and could be developed in Switzerland.

Time and cost should also be factored in when assessing the benefits of flexible design, say the researchers. Refurbishment without demolition and wet construction work is expected to take a far shorter time and result in lower noise and particle emissions.

The researchers acknowledge that the building plans they used were at pre-project stage, therefore actual quantities of building materials used may differ from projections. Nor did they consider potential future technologies regarding material recovery or energy use, and only modelled 100% replacement of components in maintenance – therefore impacts could be overestimated.

In conclusion, the flexible building considered here may not appear very advantageous in the 60-year LCA, but, if functionality, time and cost are considered, plus a longer building lifespan, the environmental performance of a flexible building becomes apparent. The major advantage is the possibility of adapting the building space to future needs, which can avoid demolition. Reversible design also decreases the amount of mixed demolition waste, increases material recirculation and facilitates separation of components.

Building designers alone cannot solve the sustainability problem, say the researchers – cleaner production, better durability of components, wider recycling and re-use are needed. For example, gypsum and mineral wool recycling should be explored, and re-use of recovered building components needs to be established to realise the full benefits of reversible design.

Footnotes:

1. European Commission (2020). A New Circular Economy Action Plan - for a Cleaner and More Competitive Europe
2. United Nations Environment Programme (2020). 2020 Global Status Report for Buildings and Construction: towards a Zero-Emission, Efficient and Resilient Buildings and Construction Sector. Nairobi, Kenya: United Nations. Available from: https://globalabc.org/news/launched-2020-global-status-report-buildings-and-construction

Source:

Kröhnert, H., Itten, R. and Stucki, M. (2022) Comparing flexible and conventional monolithic building design: Life cycle environmental impact and potential for material circulation. Building and Environment, 222: 109409. Available from: https://doi.org/10.1016/j.buildenv.2022.109409

To cite this article/service:

“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.