## 4 Discussion  
A comprehensive spatiotemporal model of the in-use stock metal roofing and cladding of case buildings was created by collaborating and promoting GIS and BIM technologies. The model contained the geometry of the building's surface area, a specific product type division, and a clear geographical location in time and space. BIM was used to turn 2D graphics into 3D time-and-space modelling with an information library and display the different product types in different colours on the space map. By having the spatial model of the case buildings, the specific product stock was quantified. In addition, there was prerequisite data for creating the model, including the construction date of the building, the floor area, the specific material type, and the height of the building. This building information must be obtained before creating a spatial model of the case buildings and is useful for further assessment, such as LCA. The study analysed and mapped ten case buildings (residential and commercial) in six different cities in New Zealand. It was found that the stock of metal roofing and cladding in commercial buildings was greater in number than that in residential buildings. The metal cladding product in residential buildings mostly covered the roofs, while in commercial buildings, it almost covered the entire surfaces of the building, including walls and roofs. Among all the case buildings, a long run roofing profile with seven ribs was only used for the residential building located at 201 Lincoln Drive, Henderson. The tray roofing profile with a pan width of 450 mm was identified to be attached in residential buildings only, and the long run roofing profile with five ribs metal product was the most common in-use metal product in the case buildings. It was found that the long run roofing with five ribs product is suitable for both residential and commercial buildings in New Zealand, performs well in wind and rain protection, and has a particular advantage in price. Furthermore, the environmental assessment of the GWP values of the investigated in-stock metal products from the case buildings was performed. The carbon emissions quantification was carried out using the LCA approach with LCAQuick. Data such as the products' quantities were utilised from the GIS modelling in the early steps of the study. The study found that the GWP values of the different investigated metal cladding and roofing products were varied. The variation in GWP values from the investigated metal cladding and roofing products was caused by the different profile designs of the products. The long run roofing profiles with seven ribs and five ribs were long run roofing systems with 0.40 mm and 0.55 mm BMT, and the investigated buildings used a range of BMT for the roofing and wall cladding systems, which can be seen in Table 3. The long run roofing profile with seven ribs product had a 934 mm width and a 36 mm height, with a 1.40 m end span and a 1.70 m internal span for the 0.40 mm BMT type, while the 0.55 mm BMT of this product had a 2.10 m end span and a 2.70 m internal span in its design. The long run roofing profile with five ribs had a 765 mm width and a 29 mm height, with a 1.10 mm end span and a 1.60 mm internal span for the 0.40 BMT type; this profile had a 1.50 mm end span and a 2.20 mm internal span for the 0.55 BMT type. The tray roofing profile with a pan width of 450 mm was a wide tray roofing system roll-formed in single-length trays. The profile had a 450 mm tray pan and a 45 mm overall height. Therefore, with a range of profile designs, the products' surface areas varied and resulted in different quantities of material required in the manufacturing processes of these products. Thus, the varied GWP values were affected by the different numbers of materials utilised in the production stages of the roofing profiles. According to Table 3, the long run roofing profile with seven ribs product had 10.93 kgCO2 eq/m\({}^{2}\) during the A1-A3, C3, C4, and D modules.