Environmental Impacts of Multi-Storey Buildings Using Different Construction Materials
The Research Goals and Objectives for this project were set out in the Ministry of Agriculture and Forestry (MAF) RFP POR/7811, April 2007. The University of Canterbury responded with a collaborative research programme ‘to fill the information gap about what is the greatest amount of wood that can be used in the construction and fit-out of commercial, large-scale buildings in New Zealand (and) …… to provide Life Cycle Assessment (LCA) information about the benefits of maximising the use of wood in sustainable buildings’. This research project modelled the performance of four similar office building designs – Concrete, Steel, Timber and TimberPlus – all based on an actual six-storey 4,200m2 building, to investigate the influence of construction materials on life cycle energy use and global warming potential (GWP). All four buildings were designed for a 60 year lifetime, with very similar low operational energy consumption. The Concrete and Steel buildings employed conventional structural design and construction methods. The Timber buildings were designed with an innovative post-tensioned timber structure using laminated veneer lumber (LVL). The TimberPlus design further increased the use of timber in architectural features such as exterior cladding, windows and ceilings. All timber materials are renewable and durable, sourced from sustainably managed forests. Predicted construction times for all four buildings are similar. The LCA study by Scion considered the full life cycle of the buildings including initial embodied energy of the materials, and maintenance, transport, operational energy and two endof- life scenarios, where deconstructed materials were either landfilled or reutilised. Increasing the amount of timber in the buildings decreased the initial embodied energy and GWP of materials and also decreased the total energy consumption and GWP over the 60 year lifetime. The TimberPlus design clearly had the lowest environmental impacts, whilst the Steel building had the highest impacts. A significant benefit could be obtained in the Steel, Concrete and Timber buildings by replacing high embodied energy components (especially aluminium windows and louvres) with timber. The final destination of deconstruction waste at the end of the 60 year life-cycle is extremely important. Landfilling of timber waste, with the permanent storage of most of the carbon in the timber, was slightly more beneficial than burning of wood waste for energy. The benefits of landfilling timber waste will increase as modern and future landfill construction and management capture and utilise more of the methane generated by decomposition. Recycling of steel and concrete is more beneficial than landfilling. It is important to note that looking at a single environmental indicator, such as GWP, could lead to unintended outcomes. For example, for the TimberPlus building the landfilling scenario would be slightly better in terms of climate change. However, looking at the energy results alongside the GWP results, the reutilisation scenario shows both an energy reutilisation benefit, as well as still being beneficial to climate change. Therefore, the use of multiple indicators may be necessary to inform the environmental decision-making process.An alternative end-of-life scenario which assumed permanent storage of carbon in wood materials showed that net total GWP for the materials in the TimberPlus building is negative, because the long-term storage of over 630 tonnes of carbon dioxide removed from the atmosphere more than cancels out all the greenhouse gases emitted in the manufacture of all the other building materials. In this scenario, the TimberPlus building could be considered to be ‘carbon-neutral’ for at least the first 12 years of its operation. With NZ-specific energy and GWP coefficients now available, a simple model can be developed for assessing the energy and GWP impacts of individual buildings. This study shows that the Green Star Office rating tool does not capture all the benefits of using more wood in buildings which are identified by the simple model or a full LCA study. Support of on-going research is essential to further develop the potential for Timber buildings to be more widely used in NZ, with subsequent reductions in greenhouse gas emissions.
SubjectsField of Research::09 - Engineering::0905 - Civil Engineering::090502 - Construction Engineering
- Engineering: Reports