Comparative life cycle and energy performance analysis of a circular office building in a temperate climate

Abstract This study evaluates the whole-life environmental and energy performance of cross-laminated timber (CLT) versus reinforced concrete in office buildings, using 't Centrum (Westerlo, Belgium), Belgium’s first certified circular CLT office building, as a real-world case study. Life cycle assessment (LCA) was conducted following ISO 14040/44 and EN 15978 (stages A1–A5, B4, B6, C3–C4; 50-year horizon), combined with dynamic energy simulation in DesignBuilder. Four construction material scenarios and four heating, ventilation, and air conditioning (HVAC) configurations were assessed. Net life cycle global warming potential (GWP) for the CLT reference scenario is 9.97 kg CO 2 e/(m 2 ·year), representing a 30% reduction compared to the best-performing concrete alternative (14.34 kg CO 2 e/(m 2 ·year)), reported using the EN 15804 + A2 − 1/ + 1 biogenic carbon convention with fossil and biogenic flows disaggregated separately. Although CLT’s lower thermal mass increased overheating risk, adding bio-based thermal inertia materials reduced thermal discomfort hours by up to 25% per EN 16798–1 adaptive comfort criteria, with negligible carbon impact (< 1%). Operational energy consumption was comparable across structural systems. HVAC equipment accounts for 68% of material-related emissions in CLT buildings due to repeated replacement cycles over the building lifespan. Sensitivity analysis (Morris method) identified the electricity mix and HVAC system type as dominant uncertainty sources. In high-performance Belgian buildings, embodied carbon, not operational energy, is the decisive lifecycle factor, and CLT combined with bioclimatic design and low-carbon HVAC systems represents a credible circular pathway toward carbon–neutral construction in temperate climates.