Circular Housing Retrofit Strategies and Solutions: Towards Modular, Mass-Customised and 'Cyclable' Retrofit Products

The building sector consumes 40 % of resources globally, produces 40 % of global waste and 33 % of CO₂ emissions. Creating a circular built environment is therefore of paramount importance to a sustainable society. The housing stock can be made more circular through circular retrofitting. However, strategies and solutions integrating circularity within housing retrofit are lacking. This paper focusses on developing a circular housing retrofit strategy and solution for Dutch housing constructed between 1970 and 1990. Through literature study, potential circular retrofit approaches are identified and translated into a general strategy. By developing a concrete retrofit solution, we illustrate how this general strategy can be applied in practice. It is found that in the Dutch context 'all-in-one' sustainable retrofits are difficult to realise. By applying modular (allowing component-by-component retrofit), 'mass-customisable', and 'cyclable' retrofit products, natural maintenance moments can be employed to gradually create a circular housing stock. As an example of such a product we describe the Circular Kitchen (CIK), which was developed together with industry. The CIK applies a plug-and-play design, separating components based on lifespan. The CIK supply-chain arranges 'relooping' of the CIK in a 'return-street' and 'return-factory'. The CIK business model applies financial arrangements such as lease and 'sale-with-deposit', motivating the return and 're-looping' of the CIK after use. In conclusion, the strategy presented in this paper has the potential to support circular housing retrofit in the Dutch context and for housing with similar characteristics. However, development of more circular retrofit products is necessary to create a fully circular housing stock over time.