Environmental Impacts of Multi-Storey Buildings Using Different ...

- 85 -The contribution of initial embodied energy and GWP to the overall life cycle results ishighest for the Steel building at 11% and 23% respectively. The end-of-life phase wasdominated by the energy used to operate a landfill and the potential methane emissions fromthe partial decomposition of timber. The carbon stored in the wood that was sent to landfill,was subtracted from the end-of-life GWP. The TimberPlus building, being composed largelyof wood, had the greatest net CO 2 eq sequestration (511 tonnes CO 2 eq), and the Steel building,containing the least wood, had the least at 14 tonnes CO 2 eq. These reductions, in terms of theoverall impact on the building’s life cycle; account for reductions of up to 9% (TimberPlus)of the total GWP. The GWP benefit from carbon stored in landfills increases as more methaneis able to be captured and converted to CO 2 (which has a much lower GWP value thanmethane). If the captured methane is used for energy (for example, as is presently happeningat Burwood landfill in Christchurch, where the methane is collected and used for energy forheating the QEII swimming pool complex) there will also be a benefit for the net primaryenergy balance over the life cycle of the buildings.6.5.3 Maintenance Related EnergyMaintenance of the buildings over the 60 year lifetime contributed relatively minorenvironmental impacts compared to the initial embodied energy and GWP. However, therewere noticeable differences, in maintenance impacts, between building types and buildingcomponents.The Steel building had the greatest maintenance related impacts, whereas TimberPlus had thesmallest. Fewer materials were required to maintain the TimberPlus building. Western RedCedar, which lasts 60+ years, was used for louvres, balustrades, and reveals. Therefore, thesestructures do not require replacement, resulting in a greatly reduced overall impact for theTimberPlus building.However, the TimberPlus building did have the greatest maintenance related impact forinterior walls and ceilings components. This is due to the replacement of MDF panels whichhave a lifetime of 40 years. Even though the TimberPlus building had a higher maintenancerelated impact from replacing MDF interior linings and ceilings, the energy recovered fromcombusting these timber components, in the reutilisation scenario, reduced the overallembodied energy. Additionally, the carbon storage in the landfill scenario and the offset ofemissions from fossil fuels in the reutilisation scenario result in GWP reductions for thesetimber components. This cannot be done for the other building types as they use materials(e.g. gypsum board) that are not combustible and, therefore, are sent to landfill.The building components that required the most maintenance, with the largest contribution tototal maintenance related impact, were the windows. This is indicative of the large quantity ofaluminium required in the maintenance of the frames. The exception is TimberPlus which hadthe lowest impact as much of the aluminium componentry of the windows is replaced withWestern Red Cedar. For the TimberPlus building, the reduced impact of the windowscategory outweighs the higher impacts in interior wall and ceiling categoriesSome studies have shown that building maintenance can be greater than the initial embodiedimpacts. Therefore, the building designs in this study are very good in comparison, asassociated building maintenance only contributes around 1% to the total impact and between11% (Steel building) and 17 % (TimberPlus) of initial embodied energy.