# Improving Sustainability of Steel Roofs: Life Cycle Assessment of a Case Study Roof
## 2 Methods and Life Cycle Assessment Processes
### Life Cycle Impact Assessment (LCIA)  
After LCI data was collated, consisting of all the material and energy inputs and outputs in each process of the roof life cycle, all emissions were converted, representing the effect on the mid-point environmental impact categories. Midpoints are recognised to be connections in the cause-effect chain (an environmental mechanism) of the impact group (e.g., ozone depletion and global warming) [70]. The CML 2001 was used as the LCIA methodology, where it was considered the most popular method in the construction industry [71]. GaBi Ts software Version 9.1.0.53 [61] was used to compile the LCI data and convert the data to environmental impacts using the CML 2001 method. In addition, seven environmental impact categories were quantified, which are outlined below. 1. Global warming potential (GWP): greenhouse gasses and global warming--fossil + biogenic
2. Ozone depletion potential (ODP): damage to ozone in the upper atmosphere
3. Acidification potential (AP): acidification of soil or water
4. Eutrophication potential (EP): over-fertilisation and excessive biomass growth
5. Photochemical ozone creation potential (POCP): impact of ozone and other oxidants in lower atmosphere
6. Abiotic depletion potential--elements (ADPE): elements, minerals and energy consumed
7. Abiotic depletion potential--fossil (ADPF): consumption of fossil resources  
GaBi modelling was conducted to quantify the environmental impacts produced by the steel roof and ancillary items. In the assessment, background LCI data from GaBi's inbuilt and Worldsteel databases was utilised. The additional information for the steel profile manufacturing in the local factory was estimated from a site visit. Due to the short nature of the study and the limitations in the available LCI data in the GaBi education database, several processes in the manufacturing process of supplementary materials were excluded. Figure 3 shows the overview of GaBi modelling for the steel roof throughout its life cycle stages. The steel coil used by the local manufacturer was supplied by a local supplier, which imported the coil from the Busan factory in South Korea. The data inputs in the coil manufacturing process used global average data. The steel coil was assumed to be shipped to Auckland, where it was transported to the local storage facility by truck. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Item**} & **Material in GaBi** & **Qty** & **Unit** & **kg/m\({}^{2}\)-Floor** \\ \hline \multirow{4}{*}{Steel} & The long run roofing profile & \multirow{2}{*}{Organic steel coil} & \multirow{2}{*}{376} & \multirow{2}{*}{Lin/m} & \multirow{2}{*}{5.800} \\  & with five ribs—0.55 mm & & & & \\ \cline{2-5}  & Ridge/barge flashing & & & & \\ \cline{2-5}  & Eave drip flashing & & & & \\ \cline{2-5}  & 125 box gutter & & & & \\ \cline{2-5}  & Internal gutter & & & & \\ \hline \multirow{4}{*}{Others} & Fascia board & \multirow{2}{*}{Pine} & \multirow{2}{*}{1–70 \(\times\) 45} & \multirow{2}{*}{4900 crs} & \multirow{2}{*}{1.500} \\  & (ridge/barge/eaves) & & & & \\ \cline{2-5}  & Timber purlins/battens & & & & \\ \cline{2-5}  & Underlay & \multirow{2}{*}{Polyppropylene film} & \multirow{2}{*}{7} & \multirow{2}{*}{50 m\({}^{2}\) rolls} & \multirow{2}{*}{0.130} \\ \cline{2-5}  & Flashing tape & & & & \\ \hline \multirow{4}{*}{Excluded} & Roof truss and brackets, & \multirow{2}{*}{10} & \multirow{2}{*}{Lin/m} & \multirow{2}{*}{0.002} \\  & fixings, softit boards, gutter & & & \\ \cline{1-1} \cline{3-5}  & brackets, downpipes, & & & & \\ \cline{1-1} \cline{3-5}  & touch-up paint, and gutter & & & & \\ \cline{1-1} \cline{3-5}  & pipe flashings & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Bill of materials for case study house. Electricity for lighting and gas for forklift handling were used in the storage site. The coil was delivered to the local steel roof factory, where the steel roof manufacturing process began (see Figure 4).