# Improving Sustainability of Steel Roofs: Life Cycle Assessment of a Case Study Roof
## 1 Introduction
Therefore, in achieving the emission reduction strategy, an assessment related to environmental impact needs to be conducted to analyse the progress of the emission reduction. A life cycle assessment (LCA) is the most well-known methodology for quantifying the environmental impact of a product, including building products [50; 51; 52; 53]. It can be used to evaluate the expected environmental impacts of a product or service throughout its life cycle, from raw material acquisition through production, distribution, use, maintenance, and disposal [54]. There are two primary approaches to LCA: process LCA and input-output (IO) LCA, but hybrid combinations of the two are also possible [55]. IO LCA determines environmental effects from macro-sector-level data of monetary flows combined with statistical environmental impact data [56]. When assessing the life cycle effects of a specific product with the goal of reducing those impacts, IO LCA is not suitable, and process LCA is typically used. It is because the emissions are assessed according to actual energy and mass flows from process to process [57]. In addition, ISO standards 14040 [58] and 14044 [25] outline a framework for LCA methodology that is used globally. According to ISO 14040:2006 [58], there are four steps to conducting LCA: goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation analysis. The goal and scope definition set the boundaries of the LCA as well as its purpose. The LCI step is a data collection step where an inventory of the materials, energy usage, direct environmental impacts, and waste is compiled from the flows and processes in the supply chain. There is typically a large amount of data in the full supply chain, and it is impractical to collect this data for each LCA. Databases such as ecoinvent and the US Life Cycle Inventory Database have widespread datasets with life cycle inventory background data for various products and processes. However, in order to produce more relevant and transparent results, the LCA study cannot rely solely on generic data from commercial databases. It has to consider more specific data for the assessment, such as an Environmental Product Declaration (EPD) of a specific product [59]. EPD is a standardized product LCA data that has relatively more accurate and reliable values by using specific foreground data. The LCIA step employs scientific methods such as CML and TRACI to characterize and characterize a large number of different environmental impacts into indicator values that can be interpreted and compared [60]. The most popular commercial tools for completing product LCA for all sectors, including construction, are GaBi Ts [61] and SimaPro [57; 62], but free software like openLCA [63] and LCAQuick [64] is also gaining popularity in current practice. Using the GaBi Ts, a process-based LCA can be performed, which suits the assessment of specific processes such as steel roofing production processes. The Worldsteel Association [65] completed an LCA of six roofing solutions for a Scandinavian house. The purpose of this LCA was to compare the environmental effects of concrete, steel, and bitumen roofing solutions available in Finland and Sweden, and they found that the steel roofing solutions had the best outcomes for all environmental categories [65]. Mitchell & Carman [7] completed LCA for various building types in NZ (industrial, residential, and office) and found that the building envelopes, including steel roofing, contribute approximately 20-25% of the total embodied carbon. Steel roofing has a more significant proportion of embodied carbon for single-storey structures, and [PERSON] et al. [10] found it could contribute more than 25% of the upfront embodied carbon for a typical New Zealand (NZ) house. However, the choice of database and software may significantly impact the reported results. It should be noted that the result can be varied due to local variations in raw material purity and electric mix. [PERSON] et al.