The transition to a Circular Economy (CE) is increasingly recognised as essential for reducing resource consumption, minimising waste, and supporting decarbonisation in the construction sector. However, the implementation of circular practices remains limited due to a range of interconnected barriers. This study examines the obstacles to Circular Economy adoption in the Irish construction sector, drawing on a review of international literature and empirical evidence from a co-creation workshop involving 40 stakeholders from government, industry, academia, and professional organisations. Using a participatory qualitative research design, barriers were identified, categorised, and prioritised through thematic analysis and comparative ranking techniques. The findings reveal that CE adoption is constrained by a complex system of economic, regulatory, infrastructural, organisational, cultural, digital, and technical barriers. Stakeholders identified lack of investment, weak economic viability of secondary materials, fragmented policy and regulatory frameworks, certification and recertification challenges, supply chain limitations, and insufficient collaboration in procurement and design as the most critical obstacles. Certification emerged as a particularly significant structural bottleneck, restricting the market re-entry of reused materials and affecting confidence, cost, insurance, and market viability. The results also highlight the importance of the Irish context, where planning delays, regional infrastructure gaps, limited reuse markets, and dependence on imported materials further constrain circular transitions. The study concludes that advancing circular construction in Ireland requires systemic reform rather than isolated technical interventions. Priority actions include strengthening circular infrastructure, reforming certification systems, developing secondary material markets, improving policy coordination, enhancing lifecycle collaboration, and expanding digital and data-driven mechanisms to support material traceability and performance measurement.