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Life Cycle Analysis — Environmental Impacts of Concrete and Other Types of Buildings |
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This article summarizes studies of a wide range of buildings from large commercial structures, to multi-story apartment buildings and single family homes. The first part looks at studies that examined only the impact linked to materials production and building construction. The second part reports the results of full life cycle of the structures. Impact of Materials Production and Building Construction Analysis of a Three-Story Office Building Life cycle assessment methods were used to examine the total energy use and CO2 emissions associated with wood, steel, and concrete construction (Forintek Canada 1997). Raw material extraction, manufacturing, all transportation, and building construction were included in the assessment. As all three of the structures were designed with concrete foundations, the only part of the structures in which different structural materials were used was the above-grade portion, and thus it is here that meaningful comparison can be made. Results: Concrete construction required 72% more energy than wood construction, but 29 % less energy than steel construction. CO2 emissions, however, were significantly higher for the concrete structure than for any other type of construction. Analysis of a Four-Story Apartment Building A life cycle assessment focused on energy and greenhouse gas emissions associated with construction of a four-story apartment building in Växjo, Sweden examined concrete and wood alternatives. The building contained 16 apartments, comprising 12,800 usable square feet (1,189 m2) in total. This study was conducted by analyzing the actual construction of a wood frame building, and then designing and analyzing (but not constructing) the same structure from reinforced concrete. Included in the analysis were raw material extraction, manufacturing, all transportation, and building construction activity. Results showed significantly higher energy consumption associated with concrete construction than with wood construction, both in the form of electricity and fossil fuels as well as a large difference in CO2 emissions. The total carbon balance over a 100 year life cycle was greater the +20 for concrete and less than - 40 for wood. Analysis of Single-Family Residential Structures The Department of Civil Engineering at the University of Christchurch, New Zealand conducted a study of the life cycle impacts of the use of concrete, wood, and steel for various components of a single-family residential structure. Energy use and carbon emissions from raw material extraction through building construction were the focus of the study which considered alternative house frame, flooring, and wall systems Taking into account the fact that wood is about one-half by weight carbon, the analysis showed concrete construction to result in greater net carbon emissions than either wood or steel in both floor and wall systems. Total carbon emissions for wood were actually negative due to the fact that the carbon stored within wood is greater than the emissions associated with harvesting and processing it. Another study, this conducted by the Consortium for Research on Renewable Industrial Materials (CORRIM) examined concrete block and wood-frame construction options for a typical home built in the Atlanta metropolitan area (Lippke et al. 2004, Perez-Garcia et al.2005). The 2,135 square foot (198 m2) house was a concrete block slab-on-grade design, with material differences only in the exterior walls. A life cycle comparison of the two designs from material extraction through building construction shows concrete construction to result in significantly higher consumption of energy, emissions of greenhouses gases (indicated by global warming potential – GWP), emissions to air, and generation of solid wastes than wood construction. A comparison of above grade portions of the structure only (which factors out the common slab foundation but which retains common elements in the interior walls and roof systems) shows a greater difference, with impacts 38% to 164% percent greater for concrete construction than for wood. However, the most meaningful comparison is one in which only the different elements are compared – in this case the exterior walls. The embodied energy difference in this instance is 149%, meaning that the materials for the concrete design require 2.49 times more energy to extract, convert to product, and incorporate into the finished structure than the wood design. Full Life Cycle Impact Studies Results obtained by many other research groups around the world who have studied these issues are consistent. Here are a few:
The Bottom Line From an environmental impact point of view, concrete construction is preferable to steel-frame construction from an energy use standpoint, but is generally disadvantageous to steel with regard to generation of CO2 and other greenhouse gases. When concrete construction is systematically compared to wood construction, results consistently show higher energy consumption and related emissions, including carbon dioxide and other greenhouse gases, associated with concrete construction. |
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| The information in this article is based upon the paper presented by Dr. Jim Bowyer and associates of Dovetail Partners, Inc. We encourage you to view the paper in its entirety at: http://www.dovetailinc.org/files/DovetailConcrete0808zb.pdf
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