## 4 Discussion
The five ribs product's long-run roofing profile had a range of GWP values among the investigated buildings that attached this product to their roofing and cladding systems. The product had total carbon emissions ranging from 6.16 to 12.58 kgCO2 eq/m\({}^{2}\) during the assessed building life cycles, while the tray roofing profile with a pan width of 450 mm produced GWP values ranging from 9.83 to 14.11 kgCO2 eq/m\({}^{2}\). The production stages of roofing and wall cladding metal products were the greatest GWP value emitters compared to other assessed life cycle stages. The long run roofing profile with the seven ribs model's production stages emitted 15.60 kgCO2 eq/m\({}^{2}\); the five ribs model's average emissions were 15.31 kgCO2 eq/m\({}^{2}\); and the tray roofing profile produced 17.45 kgCO2 eq/m\({}^{2}\) during these life cycle stages. The study aligned with the LCA report from Thinkstep ANZ regarding the emissions from the production of steel roofing and cladding products in New Zealand. The report found that emissions from the 0.40 mm and 0.55 mm BMT roll-formed roofing and cladding in New Zealand were between 11.2 and 18.3 kgCO2 eq/m\({}^{2}\)[77]. However, the values are different from those in the Athena Sustainable Materials Institute report, which found that the carbon emissions from steel cladding production processes in Canada ranged from 7.74 to 10.42 kgCO2 eq/m\({}^{2}\)[78]. The difference between the study and the Athena results was caused by the different geographical conditions, leading to the carbon emissions gap. Besides that, the C3 and C4 modules only made up a small amount of GWP, which was about 0.48% of all tested metal products. When considering the products' recycling, reusing, and recovering stages, a potential carbon offset of up to 34% of the GWP values produced from the production stages can be achieved. Figure 4 compares the average GWP values from the production stages and the potential carbon offset after the EOL processes for each specific metal product. The study found no significant difference between the three products' potential carbon offsets in the future. The investigated long run roofing profile with the seven ribs model had a possible 30.28% carbon savings per one meter squared of production of the product. The long run roofing profile with the five ribs model had a potential carbon offset range between 29.11% and 30.81%, while the tray roofing profile with a pan with 450 mm ranged from 31.14% to 33.61%. The high percentage of potential carbon offset of steel products was driven by steel's relatively high recovery rates for recycling. The role of recycling, reuse, and recovery seemed to be necessary due to the high benefits in the future of reducing the carbon emissions from the buildings, especially the roofing and wall cladding systems. In New Zealand, 75% of the waste steel sheet's mass proceeds to the recycling process for the typical practise [57]. This value led to the higher potential of the steel roofing and wall cladding having carbon offset after the EOL processes. Steel can be made either from virgin raw materials or from reclaimed materials. However, the production process from raw materials can result in five times the embodied energy and carbon than using recycled materials [79]. Therefore, carbon emissions can be reduced if steel roofing and wall cladding are recycled and used to make new products. The study focused on analysing the environmental impact of GWP in the production stages and recycling stages of specific metal roofing and wall cladding products. Simultaneously, the study promoted the use of GIS technology and the LCA approach in quantifying the GWP values of building products, laying the foundation for the future development of the CE. The research model can be used not only for metal products but also for other building materials, such as brick and timber. It can provide good suggestions for the CE approach in the construction industry.