This Design for Interaction master thesis is focussed on the development of a design intervention to encourage consumer behaviour towards DIY repair and upgrading of furniture. The project was carried out in collaboration with the Behaviour Insights Team of the Ministry of Infrastructure and Water Management and Het Groene Brein. Problem background: Furniture is a product category which causes a large environmental impact due to the materials they contain and consumers’ current replacement behaviour. In the Netherlands, over half of the large amount of disposed furniture pieces have not reaching the end of their lifespan (Koch & Vringer, 2023). Increasing repair and upgrading behaviour can extend the life of damaged or undesired furniture pieces and thereby reduce environmental impact. Research & design goal: Literature research, generative sessions, a survey and expert interviews were used to determine how a design intervention can most effectively contribute to the desired behaviour change. It was concluded that the design should support 18-35 aged, high income, high education consumers, living in the big cities, to ... 1. … make a plan with a desired outcome for ... 2. … together perform ... ... DIY repair and/or upgrade activities for furniture from the low/medium priced segment made from wood and/or textile and foam in 2024. Design proposal: The outcome of this master thesis is a design intervention named ‘Opknappers,’ a proposal for Intergamma (the umbrella organization of Karwei and Gamma). The proposal includes DIY cards and an exposition showcasing and explaining repair/upgrade possibilities in the physical shops. Additionally, a concept for the Opknappers app has been developed, which allows consumers to visualise upgrade options for their own furniture. Finally, a plan was made for using Intergamma’s websites and social media to support consumers in the DIY process. The final design was evaluated with customers and employees of Intergamma, and final improvements and recommendations were made.