Today’s construction industry is the most resource-intensive and wasteful industry which causes far-reaching socio-environmental problems. As a consequence, there is a growing call to change this way of constructing. The circular economy (CE) concept is put forward as a promising alternative. Creating a circular model of material use and considering buildings as valuable material banks are regarded as the pivot towards a sustainable and resilient built environment. However, building designers are lost in the shuffle on how this circularity thinking can be integrated in building design. Moreover, at present, the multifaceted profession of architects causes a complex and packed workflow, where fitting in innovative concepts is considered more of a burden than a relief.

Therefore, the main objective of this research is to develop actionable knowledge and insights that enables designers to make better-informed design choices during the design process and so support the transition towards a circular economy in the building sector.

Through participative action research (PAR), where numerous interviews and workshops were held with building designers, infused with literature research on sustainability interventions, the thesis offers a framework of circular interventions that can be undertaken during the design process. A second outcome is a methodological contribution to identify, prototype, and validate such interventions. Following that, this research produced some ready-to-use tools for building designers, such as an online platform and workshop formats. Ultimately, the ‘interventions for circular architecture’ can play the role of a guiding light for building designers as they illustrate how future design processes can be managed and have a positive impact on many.

Affordable and environmentally-friendly houses are high on the agenda in Flanders. To be able to generate financially, socially and environmentally sustainable dwellings, an alternative is required for the current housing stock. What if our houses were adaptable to our needs and not the other way around? This research sought an answer by exploring the potential of expandable houses.

An expandable house consists of a core house and has the possibility to add or expand spaces. The core house is a complete house and includes the mandatory functions to accommodate one or two persons. The core and the expansions are designed so that they can anticipate and adapt to changing needs. This requires that the future is considered in the design phase. In order to take into account the uncertainty of the future and to show that the expandable house can withstand time, scenarios of family households were generated. The core house is thus designed in such a way that it can adapt to the different household scenarios by means of expansion.

Then, the material efficiency and the life cycle costs of the expandable house were calculated for each scenario. To demonstrate the benefits of the anticipated expansions, the material efficiency and the life cycle costs of the expandable house is compared with those of a conventional row house in Flanders.

In terms of costs, both the initial costs and the life cycle costs are lower for an expandable house than for a conventional house. Also in terms of environmental impact, the expandable house is more favorable because less materials are needed to build it. Furthermore, using demountable and lightweight materials facilitates adaptability, but it has also a favourable impact on the environment. A remarkable finding is that it does not matter, in terms of costs, whether the core house and the extensions are built out of conventional or out of demountable materials. Only if the house would shrink at a given moment, there is a difference. When using demountable elements, they can be disassembled, sold and reused in another project. This approach can even imply profit. Building elements that are broken down when they have not reached their maximum lifespan thus result in ecological and financial costs.

The exploration into life cycle costs, material efficiency and adaptability of expandable houses underpins supports the hypothesis that transformable housing is a possible catalyst for sustainable development in the housing sector. Households, architects and entrepreneurs benefit from the social, economic and ecological qualities it generates over time.