The built environment is at a tipping point, faced with the dual imperatives of rapid urban growth and deep decarbonisation. Mass timber construction (MTC) has emerged as a disruptive technology, promising reduced embodied carbon, rapid prefabrication, and enhanced design flexibility. However, to fully realise a sustainable transition, construction must go beyond material substitution and embrace circularity and adaptability at every stage. The presentation draws on recent research - including global stakeholder perspectives and empirical modelling - to examine how mass timber can catalyse a shift toward circular building practices and adaptable design, using Open Building principles. Key findings demonstrate that MTC is uniquely positioned to support long-term adaptability and occupant agency, while also driving decarbonisation leadership within the sector. Mediation analyses reveal that perceptions of environmental impact and circular practice are significant predictors of support for Open Building, with decarbonisation leadership acting as a key pathway. The discussion highlights practical strategies for integrating circularity and adaptability in real-world projects, and outlines the policy and industry shifts needed to unlock mass timber’s full potential. Ultimately, the case is made for rethinking not just what we build with, but how we build and, crucially, how our buildings can evolve over time.