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

- 60 -It was assumed that structural components and insulation would last the entire lifespan of thebuilding of 60 years. It was also assumed that any replacements required, would be with anidentical material to the original.The replacement or refurbishment lifetime for acoustic ceiling tiles was estimated at 40 yearsand building components produced from Western Red Cedar were estimated to last 60+ years,except for windows which were assumed to last 40 years, provided there is strict adherence toa regular maintenance, such as staining (Nicholls, 2008).6.3.3.3 End-of-Life InventoryBase ScenarioThe base scenario assumes that all building materials, including wood-based materialsinstalled in each building, such as timber, LVL, plywood, and MDF, would be sent to landfillfollowing deconstruction at the end of each building’s life. For the landfill scenarios thetransport to the landfill as well as all emissions to the operating the landfill (e.g. use of bulldozers) are included (GaBi, 2006).The total mass of all the structural timber, architectural finishes and each wooden componentfor each building is presented in (Table 6.2). The carbon content of all wooden materials wasassumed to be 50% (Wegener and Fengel, 1982; IPCC, 2006). The total carbon within thewooden materials sent to landfill was calculated for each building (i) based on this proportion(Table 6.2). Evidence has shown that 18% of carbon in wooden materials decomposes within19-46 years following initial disposal but after this period no further significant amount ofcarbon is released (shown as Total carbon stored in landfill after 46 years (ii))(Ximenes, et al.,2008). In lines iii) and iv) respectively those figures have been converted into CO 2 equivalentstorage.From the proportion of carbon released, 50% of that will form into carbon dioxide (CO 2 ) and50% into methane (CH 4 ) (IPCC, 2006). A 42 % capture of methane has been taken intoaccount (MfE, 2009). It is anticipated that the amount of landfill gas captured from NewZealand landfills will increase in the future; however to avoid additional uncertainties, thelatest figure based on physical data has been used. It was assumed that the captured methanewas flared and thus converted to CO 2 for the calculations 4 . Another assumption was that 10%of the non-captured methane underwent microbial oxidation to CO 2 in the landfill (IPCC,2006, Einola et al., 2009). Based on this information the total release of Greenhouse Gas(GHG) from decomposition was calculated. The total release of GHG from decompositionwas then converted into respective GWP by multiplying each GHG by its GWP coefficient,CO 2 being 1 and CH 4 , 25 (IPCC, 2007). The resultant GWP CO 2 –equivalent (v) was thensubtracted from the total CO 2 sequestered in the building (iii). This provided the net amountof CO 2 –equivalent sequestered in landfill once decomposition has ceased (vi).Due to its high GWP methane contributes around 76% to the total GWP of emissions fromlandfill.4 Data on the amount of energy produced from landfill gas in New Zealand is available, however theuncertainties associated with attributing this to specific materials make this calculation very difficult. Although itcan not be quantified at this stage, an additional benefit should be attributed to timber stored in landfills due theuse of landfill gas for energy generation.