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In response to increasing sustainability concerns and the risks of greenwashing, the European Commission's "Green Claims Directive" strives to establish reliable and standardised green product labelling. Concurrently, the demand for Environmental Product Declarations, fuelled by Sweden's climate declaration regulation, underscores the critical need for transparency and reliability in evaluating environmental impacts.This study conducts a comparative analysis of wood and steel construction environmental impact. Multiple studies highlight substantial differences in greenhouse gas emissions between timber and steel buildings. This report aims to assess and compare the differences in a wall construction of wood opposed to steel based on differences in the environmental product declarations and investigate the reasons for these differences. From production to disposal, wood's carbon retention contributes to its lower environmental impact, while steel's recyclability offers potential for reducing its impact. Additionally, decarbonisation strategies, such as biogenic carbon assessment and biomass balancing, are explored for their role in advancing renewable energy and reducing fossil fuel dependence. Furthermore, the report examines three wall constructions for exterior load-bearing walls: wooden stud, steel column and stud, and prefabricated massive timber walls made of Cross-laminated timber. Using AutoCAD Revit, these constructions will be presented and modelled, followed by environmental impact assessments in OneClickLCA. A comparison of environmental product declarations will be conducted to identify similarities and differences, aiding in material selection for environmental impact calculations. More specifically, the wall constructions are for a four-storey multifamily building with structural exterior walls. Wooden and steel frame designs will be modelled, with wooden walls featuring double studs and steel walls reinforced with columns. The Cross Laminated Timberconstruction is assumed to be sufficient due to its robust nature. No load-bearing capacity calculations will be performed. Using OneClickLCA, the method compared the environmental impacts of wooden, cross-laminated timber and steel wall constructions. Wood showed the lowest impact, emitting 315kg CO2 per 10 m2, while steel had the highest at 582 kg CO2. The product stage (A1-A3) accounted for 86-90 % of the impact, while construction processes (A4 and A5) play a smaller role. Recycling practices were found to reduce environmental impact, especially in steel production. Analysing Environmental Product Declarations reveals the significance of raw material extraction, often overlooked in wood declarations. Recycling practices, especially in steel production, contribute to reducing the overall environmental impact. Despite steel's higher reusability, wood offers potential for emission reduction through reuse or recycling. Integrating recycling into assessments supports a circular economy approach, although uncertainties remain about end-of-life scenarios. Previous research confirms the environmental benefits of timber construction, demonstrating significantly lower global warming potential compared to steel and concrete alternatives.