| doi:10.3850/978-981-08-6218-3_SUS-Th033 |
 Final Paper PDF
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COMPARATIVE CO2 EMISSIONS CONSIDERATIONS IN STEEL CONSTRUCTION
SUMMARY
Michael Roddy1 and Reynaud Serrette2
1Researcher, Pacific Energy Management, Vashon, Washington USA.
greenframe@aol.com
2Professor of Engineering, University of Santa Clara.
rserrette@scu.edu
Building on prior published work (tinyurl.com/yc8ncuq, tinyurl.com/ycxfsqu), the authors seek to determine the relative CO2 emissions scores of the three most common house framing construction materials in the United States: steel, lumber, and masonry block. A design was chosen that is adaptable to all three materials, and features a typical 3 bedroom, 2 bath modest sized American home of roughly 116 square meters.
The first stage in this process was to collect emissions intensity data from the three industries. For steel and concrete block, CO2 emissions per ton of product was collected. Wood products are measured in cubic feet, so American government harvesting data was accessed, emissions intensity per cubic meter determined, and ratios developed for use as framing lumber.
Steel products emit roughly 19% more CO2 by weight than the steel itself. Concrete block emissions are about 8% of the delivered product, though this figure was less precise, due to the dispersed and variable nature of the concrete industry.
Wood product CO2 emissions were more difficult to determine for the US, since as a non signatory of Kyoto the United States does not record land use emissions except as net sequestration. The result is that even as the US logging industry is responsible for major amounts of additional atmospheric CO2, gross data would imply that the industry is carbon negative, and PR efforts reinforce this impression.
Through accessing raw data from scientific papers, EPA annexes, and comparable country reports, we were able to estimate the CO2 intensity of wood products in the US at .96 tons per cubic meter of harvested roundwood. We then calculated US wood products consumption at slightly 599 million cubic meters annually, applied the .96 formula to yield 575 megatonnes of annual CO2 emissions, and then made calculations as to the US housing lumber consumption ratio (17.34%) and the specific application to our sample house.
The next step was to design the house according to the location in Texas for the three different structural systems. We then recruited general contractors to produce materials lists. For the steel and wood versions, two different contractors were independently asked to provide takeoffs, and the results averaged. For the block house, only one estimate was obtained, since the error bar is lower for masonry block quantities. We specified a steel truss roof system for the masonry block house, since it is more suitable for this construction, and because it would result in a lower overall emissions score for this house.
A similar exercise was undertaken by the American timber industry for a Minneapolis house in the CORRIM report, but we believe that the methodology was flawed in many respects: steel was heavily overdesigned, and emissions measurements were undertaken according to timber industry protocols, not those of carbon scientists. As a result, timber was announced to be a much lower emitter of CO2 in this application. In the absence of alternative studies, many organizations accepted this result from the CORRIM report. A more accurate accounting of this key environmental consideration is warranted, and this helped motivate our work.
The outcome of our work was startling: If the steel emissions score for the Texas house was given a value of 1, the masonry house was measured at 1.52, and the wood framed house at 6.01.
Since this data is likely to be disputed, it’s worthwhile to consider the methodology employed, and for an independent researcher to investigate the source data. For the steel house, since emissions in the industry are accurately monitored by the US Environmental Protection Agency, little variability is expected. The steel emissions score appears in Energy Information Administration reports, and derives from measured mill energy and process emissions.
The concrete industry could make a reasonable case to lower their emissions score on the grounds that concrete products sequester CO2 over time through the process of calcination. Since we do not have good data for this process in this application, it was not included in the analysis.
The US timber industry can be expected to dispute their CO2 emissions result, however, forest carbon experts, many of whom were interviewed for prior published work, generally support the values reported in this paper. Harvested wood products credits, for example, could add only 15% net site sequestration.
Due to the incendiary nature of the data in this paper, fierce disputes can be expected. This was noted to have occurred at IPCC land use conferences, where country delegations were often dominated by timber industry associated foresters.
If American or international steel firms make the decision to defend these basic results, and to project them in marketing campaigns aimed at product substitution, a thorough and comprehensive effort will be required. All elements of steel corporate management will need to act cooperatively, so that this key information does not become muddled or falsely discredited. If steel corporations do decide to leverage this favourable emissions information, steel firms, the natural environment, and the climate stand to benefit enormously.