# Improving Sustainability of Steel Roofs: Life Cycle Assessment of a Case Study Roof
## 3 Results  
### Life Cycle Assessment of Organic Coated Steel Coil  
The production of coated steel coil involved the production of steel coil from raw materials, which was then coated to provide the desired finish and durability. The environmental effects of NZ's popular coated steel coil products were compared to generic Worldsteel data derived from the Gabi Ts software. Colorsteel is the most popular pre-painted steel roofing cladding made from steel coil supplied by a local supplier. The EPD from Colorsteel was used to calculate the locally sourced products' impacts and compare them with the results of the GaBi modelling using the Worldsteel LCI data. Outputs from the GaBi Ts software for the life cycle impacts of the various categories are shown in Figure 5.  
A comparison of the life cycle impacts of steel coils sourced locally and imported steel coils represented by average Worldsteel global data is presented in Table 2. Although the comparison cannot be made with certainty, the comparison shows that imported steel coils were likely to have lower impacts in all categories than the coils produced locally.  
Figure 4: Overview of the factory production aggregate process.  
One of the reasons for the differences in impacts was likely due to the unique processes used in New Zealand to manufacture steel entirely from iron sand found along the west coast. The magnetite ore in the iron-sand was locked in with impurities such as titania and silica, and separating these requires additional heat and processing [72], resulting in greater  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Impact Category**} & \multirow{2}{*}{**Unit**} & \multicolumn{2}{c}{**1 m\({}^{2}\) of 5-rib Trapezoidal Steel Profile**} \\ \cline{3-4}  & & **Imported Organic Coated Steel Coils** & **Locally Sourced Organic Coated Steel Coils** \\ \hline Global Warming Potential & kg CO\({}_{2}\)-eq & \(1.49\times 10^{1}\) & \(2.20\times 10^{1}\) \\ \hline Ozone Depletion & kg CFC11-eq & \(-4.21\times 10^{-9}\) & \(4.85\times 10^{-9}\) \\ \hline Acidification & kg SO\({}_{2}\)-eq & \(4.42\times 10^{-2}\) & \(1.99\times 10^{-1}\) \\ \hline Eutrophication & kg PO\({}_{4}\)-eq & \(3.81\times 10^{-3}\) & \(1.05\times 10^{-2}\) \\ \hline Photochemical Ozone & kg C\({}_{2}\)H\({}_{4}\)-eq & \(6.93\times 10^{-3}\) & \(1.11\times 10^{-2}\) \\ \hline Abiotic Depletion—Elements & kg SB-eq & \(8.37\times 10^{-5}\) & \(1.79\times 10^{-4}\) \\ \hline Abiotic Depletion—Fossil & MJ & \(1.61\times 10^{2}\) & \(2.84\times 10^{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of the life cycle impacts of the imported and locally sourced organic coated steels.  
Figure 5: Outputs from GaBi showing the environmental impacts of organic steel coil production for 1 m\({}^{2}\) of roof: (**a**) GWP; (**b**) AP; (**c**) EP; (**d**) ODP; (**e**) ADP elements; (**f**) ADP fossil; (**g**) POCP.  
emissions. The average global life cycle impact was also lower because more recycled steel and more electric arc furnace production methods were used in some parts of the world.  
The results demonstrated that using imported steel coils results in a lower life cycle impact for a building project. However, care should be taken since generic data was compared with specific data from EPDs in the study. It is possible that a selected batch of imported steel coil purchased from the global market is manufactured with higher emissions than the locally sourced materials.