Environmental Impacts of Multi-Storey Buildings Using Different Construction Materials

Abstract

The Research Goals and Objectives for this project were set out in the Ministry of Agriculture
\nand Forestry (MAF) RFP POR/7811, April 2007. The University of Canterbury responded
\nwith a collaborative research programme ‘to fill the information gap about what is the greatest
\namount of wood that can be used in the construction and fit-out of commercial, large-scale
\nbuildings in New Zealand (and) …… to provide Life Cycle Assessment (LCA) information
\nabout the benefits of maximising the use of wood in sustainable buildings’.
\nThis research project modelled the performance of four similar office building designs –
\nConcrete, Steel, Timber and TimberPlus – all based on an actual six-storey 4,200m2 building,
\nto investigate the influence of construction materials on life cycle energy use and global
\nwarming potential (GWP).
\nAll four buildings were designed for a 60 year lifetime, with very similar low operational
\nenergy consumption. The Concrete and Steel buildings employed conventional structural
\ndesign and construction methods. The Timber buildings were designed with an innovative
\npost-tensioned timber structure using laminated veneer lumber (LVL). The TimberPlus design
\nfurther increased the use of timber in architectural features such as exterior cladding, windows
\nand ceilings. All timber materials are renewable and durable, sourced from sustainably
\nmanaged forests. Predicted construction times for all four buildings are similar.
\nThe LCA study by Scion considered the full life cycle of the buildings including initial
\nembodied energy of the materials, and maintenance, transport, operational energy and two endof-
\nlife scenarios, where deconstructed materials were either landfilled or reutilised.
\nIncreasing the amount of timber in the buildings decreased the initial embodied energy and
\nGWP of materials and also decreased the total energy consumption and GWP over the 60 year
\nlifetime. The TimberPlus design clearly had the lowest environmental impacts, whilst the Steel
\nbuilding had the highest impacts. A significant benefit could be obtained in the Steel, Concrete
\nand Timber buildings by replacing high embodied energy components (especially aluminium
\nwindows and louvres) with timber.
\nThe final destination of deconstruction waste at the end of the 60 year life-cycle is extremely
\nimportant. Landfilling of timber waste, with the permanent storage of most of the carbon in
\nthe timber, was slightly more beneficial than burning of wood waste for energy. The benefits of
\nlandfilling timber waste will increase as modern and future landfill construction and
\nmanagement capture and utilise more of the methane generated by decomposition. Recycling
\nof steel and concrete is more beneficial than landfilling.
\nIt is important to note that looking at a single environmental indicator, such as GWP, could
\nlead to unintended outcomes. For example, for the TimberPlus building the landfilling scenario
\nwould be slightly better in terms of climate change. However, looking at the energy results
\nalongside the GWP results, the reutilisation scenario shows both an energy reutilisation benefit,
\nas well as still being beneficial to climate change. Therefore, the use of multiple indicators
\nmay be necessary to inform the environmental decision-making process.An alternative end-of-life scenario which assumed permanent storage of carbon in wood
\nmaterials showed that net total GWP for the materials in the TimberPlus building is negative,
\nbecause the long-term storage of over 630 tonnes of carbon dioxide removed from the
\natmosphere more than cancels out all the greenhouse gases emitted in the manufacture of all
\nthe other building materials. In this scenario, the TimberPlus building could be considered to
\nbe ‘carbon-neutral’ for at least the first 12 years of its operation.
\nWith NZ-specific energy and GWP coefficients now available, a simple model can be
\ndeveloped for assessing the energy and GWP impacts of individual buildings. This study
\nshows that the Green Star Office rating tool does not capture all the benefits of using more
\nwood in buildings which are identified by the simple model or a full LCA study.
\nSupport of on-going research is essential to further develop the potential for Timber buildings
\nto be more widely used in NZ, with subsequent reductions in greenhouse gas emissions.