The European building sector is undergoing a decisive shift towards decarbonisation, in line with climate targets and the principles of a circular economy. Achieving this requires integrating sustainable materials with high-performance retrofit strategies, especially for the large stock of existing multi-family buildings that do not meet current energy efficiency and environmental standards. This study investigates the impact of different wood-based façade retrofit configurations on the energy performance and environmental footprint of a typical multi-apartment residential building in southern Sweden undergoing renovation to meet Nearly Zero Energy Building (NZEB) standards.
Three façade systems are evaluated: thermally modified wood (ThermoWood®) cladding, conventional untreated wood (spruce) exterior panel, and a composite wood-aluminium system. These are evaluated within a dynamic simulation framework that integrates cost-optimal energy efficiency measures (EEMs), including enhanced envelope insulation, high-performance windows, and heat recovery ventilation. The reference (pre-renovation) building for the analysis was built in the 1970s, with annual energy use of 133 kWh/m² for space heating, domestic hot water, and facility electricity.
To support holistic decision-making, the study integrates Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) methodologies. A cradle-to-grave LCA is conducted following EN 15978, with a 50-year reference study period. The LCA quantifies the Global Warming Potential (GWP), Acidification Potential (AP), and Eutrophication Potential (EP) for each façade system variant, considering both the material-related impacts and operational energy savings achieved through the renovation. System boundaries encompass the product stage (A1–A3), transport (A4), construction (A5), operational energy (B6), and end-of-life (C1–C4), with biogenic carbon flows accounted for in accordance with EN 16485. The material-related impacts (A1–A5 and C1–C4) are modelled using data from product-specific environmental product declarations in accordance with EN 15804. The operational energy performance and impacts (B6) are modelled using the dynamic hourly energy simulation tool IDA ICE, applying climate data for Växjö. The LCCA is conducted taking into account the investment costs associated with materials and installation of the façade systems, calculated using typical Swedish construction works tariff from Sektionsfakta, Wikells.
The analysis shows that all three façade variants significantly reduced operational GWP over the 50-year life cycle compared to the pre-renovation baseline. In the LCA, the untreated spruce cladding exhibited the lowest total GWP due to low embodied emissions, and minimal processing requirements while the thermally modified wood showed slightly higher GWP than untreated wood, reflecting energy-intensive modification processes, yet still outperformed the composite wood–aluminium system.
This integrated approach proposed in this study provides a comprehensive evaluation of how material choices affect both operational performance and long-term sustainability, showing environmental trade-offs between embodied carbon of façade material selection and operational carbon performance. The findings aim to guide NZEB retrofit strategies and support policy recommendations by emphasizing the critical role of wood-based façade material selection in achieving energy efficiency, environmental impact reduction, and cost-effectiveness.
Keywords: Nearly Zero Energy Building (NZEB), Wood façade, Environmental footprint
Authors
Youcef Boussaa
Linnaeus university, Sweden
Ambrose Dodoo
Linnaeus university, Sweden
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