Buildings and infrastructure are responsible for over 30% of the UK's carbon emissions, produce over 60% of the UK's waste, and consume approximately 50% of all extracted materials globally. Radical change is urgently required to achieve a sustainable construction sector. The circular economy (CE) is a well-recognised opportunity to turn waste into resources while reducing carbon emissions. CE aims to keep materials at the highest value possible, via a hierarchy of strategies, e.g. first prioritising extending the lifetime of buildings, then reusing building elements directly in-situ or on another site, then remanufacturing elements, and finally recycling material to conserve resources and avoid disposal. However, CE is still far from typical construction practice. Action to date has largely focused on one-off case studies of individual buildings, or recycling targets leading to wasteful downcycling, and lacks the national-scale, systems-level impact that is so desperately needed. BuildZero's vision is one of a building stock that delivers the UK's space requirements but no longer relies on extraction of new resources, by leveraging the CE to meet materials needs, and eliminating both waste and carbon emissions from material extraction and production. Using this highly ambitious end goal as a springboard, we will explore CE solutions across multiple scales, identified, co-created and co-delivered with our highly engaged industrial consortium, assess the extent to which this vision is achievable nationally, regionally and in relation to individual buildings, and determine the conditions in which the BuildZero vision leads to favourable social, environmental, and economic outcomes. This new knowledge base will provide a platform to enable these solutions to be translated into practice at scale, catalysing regional and national policy to stimulate real change. To achieve this, we will develop an interdisciplinary, multi-scale systems model of buildings and resources flows, focused around four themes: Theme 1: How does the baseline state of the system, including the interplay between societal attitudes, current materials/buildings and legislation constrain moves towards a co-created vision? Theme 2: How far can solutions that make the best use of space take us towards this vision? Theme 3: How far can making the best use of materials, including waste resources, take us? Theme 4: How can our future needs & potential solutions combine to achieve a BuildZero future? To tackle these research challenges we will use methods from industrial ecology, to understand material stocks and flows; from architecture, structural engineering, and materials science, to understand the technical potential of CE solutions; from social sciences, to understand social attitudes and trade-offs; and from economics, to understand potential CE business models. As well as conducting novel research in each underpinning area, we will commit significant resources to working with stakeholders to synthesise findings on what a CE for buildings looks like, by creating interactive foresight/backcasting tools, co-creating future scenarios and identifying the actions needed to catalyse change. Demonstrator projects will apply research to specific contexts, generating early impact. We will build a fundamental understanding of how and when to implement CE strategies, investigating economic viability, social inclusivity, and zero-carbon compatibility, considering these across multiple geographical and policy scales. Our programme of research will culminate in the identification of pathways to achieve the BuildZero vision over different time frames, and a co-created 10 year research roadmap that outlines the remaining work required to deliver a BuildZero future.