The Circular Economy of Steel Roofing and Cladding and Its Environmental Impacts—A Case Study for New Zealand

This paper investigates the environmental impacts of two commonly used steel roofing and wall-cladding products in New Zealand over their life cycle, taking into consideration the recycling process. The recycling process of steel is in line with the Circular Economy (CE) approach, where the goal is to prolong the material’s lifetime and possibly reduce its environmental impacts and material waste. Although the benefit of recycling steel is well recognised, the environmental impact values of different specific steel products cannot be generalised and need to be estimated. For this, life cycle assessment (LCA) methodology and Environmental Product Declaration (EPD) were implemented to quantify the environmental impacts of the investigated steel products and to analyse the significance of the recycling process in reducing the impacts on the environment. This study considered modules C1–C4 and D to estimate the impacts of steel products. It was found that the recycled steel materials have an effect on reducing the environmental impacts, particularly the global warming potential (GWP) and photochemical ozone creation potential (POCP), both of which were negative and of −2.36 × 106 kg CO2eq and −8.10 × 102 kg C2H4eq, respectively. However, it is important to note that not all impacts were reduced by recycling steel, which creates trade-offs within each impact indicator. In addition, when compared with locally sourced material cladding, the imported material cladding had a 6% higher negative impact value for both GWP and POCP.