Greenhouse gas balances in building construction:: wood versus concrete from life-cycle and forest land-use perspectives

In this paper, primary energy use and carbon dioxide (CO2) and methane (CH4) emissions from the construction of a multi-storey building, with either a wood or a concrete frame, were calculated from life-cycle and forest land-use perspectives. The primary energy input (mainly fossil fuels) in the production of building materials was found to be about 60-80% higher when concrete frames were considered instead of wood frames. The net greenhouse gas (GHG) balance for wood materials will depend strongly on how the wood is handled after demolition of the building. The net GHG balance will be slightly positive if all the demolition wood is used to replace fossil fuels, slightly negative if part of the demolition wood is re-used, and clearly positive if all wood is deposited in landfills, due to the production of CH4. However, if the biogas produced is collected and used to replace fossil fuels, the net GHG emissions will be insignificant. If concrete frames are used, the net GHG emissions will be about those when demolition wood from the wood-framed building is deposited in landfills and no biogas is collected. We have considered that the CO2 released from the chemical processes in the production of cement will be re-bound to the concrete by the carbonisation process. Otherwise, the net GHG emission would be more than twice as high when concrete frames are used. If forest biomass is used instead of fossil fuels, the net area of forest land required to supply both raw material and energy for the production of building materials, will be about twice as high when wood frames are used instead of concrete frames. However, the GHG mitigation efficiency, expressed as CO, equivalents per unit area of forest land, will be 2-3 times higher when wood frames are used if excess wood waste and logging residues are used to replace fossil fuels. The excess forest in the: concrete frame alternative is used to replace fossil fuels, but if this forest is used for carbon storage, the mitigation efficiency will be higher for the first forest rotation period (100 yr), but lower for the following rotation periods. Some of the data used in the analyses are uncertain, but an understanding of the complexity in comparing different alternatives for utilising forest for GHG mitigation, and of the fact that the time perspective applied affects the results markedly, is more important for the results than the precise figures in the input data. (C) 2000 Elsevier Science Ltd. All lights reserved.