Life Cycle Economic and Environmental Assessment of a Traditional Swedish Röda Stuga: A Comparative Analysis of Retrofit and NZEB Reconstruction

The evaluation of intervention strategies for the existing building stock, within the context of energy transition and increasing attention being given to sustainability, requires approaches capable of systematically integrating economic and environmental dimensions over the entire building life cycle. From this perspective, the present study develops and applies an integrated Life Cycle Costing (LCC) and Life Cycle Assessment (LCA) model aimed at comparing two alternative intervention strategies for traditional residential buildings: conservative retrofit of the existing structure and demolition with reconstruction according to Nearly Zero Energy Building (NZEB) criteria. The methodological framework, compliant with ISO 15686-5 and based on a simplified LCA-oriented approach inspired by EN 15978 principles, is applied to a representative case study of Swedish vernacular wooden architecture (röd stuga) located in the municipality of Falun. The assessments are carried out over 50- and 100-year time horizons, adopting Net Present Value (NPV) as the primary economic indicator and Global Warming Potential over 100 years (GWP100) and Cumulative Energy Demand (CED) as environmental indicators. The results show that the NZEB scenario, despite higher initial investment costs, achieves a significant reduction in life-cycle environmental impacts, with a decrease of approximately 20–25% in terms of GWP100 and about 45–50% in terms of CED compared to the retrofit scenario. The analysis also highlights a differentiated behavior of environmental indicators—while operational energy use remains dominant in cumulative energy demand, embodied impacts become increasingly significant in the GWP balance, particularly in high-performance scenarios. From an economic perspective, conservative retrofit results in lower global costs over the considered time horizons, although the economic gap tends to narrow in the long term. The integrated LCC–environmental assessment approach highlights the economic–environmental trade-offs and provides a replicable decision-support framework for sustainable regeneration policies targeting the existing residential building stock.