The Center for American Progress Article

Which Emits the Most CO2 in Home Construction: Steel, Concrete, or Timber?

– A Critical Review

by
Dr. Jim L. Bowyer [1]

Introduction

The last week of July marked the release of a posting by the Center for American Progress Which Emits the Most CO2 in Home Construction: Steel, Concrete, or Timber?[2] In response to the question “What’s the most CO2 friendly method of building a home?” the reader of the post is informed that: “Surprisingly, it’s not timber. The answer is steel, which has a CO2 index of 1 compared to 1.52 for concrete and 4.44 for a timber-framed house.”

Life-cycle studies conducted worldwide have repeatedly confirmed that CO2 emissions (or more properly CO2e emissions) attributable to timber construction are markedly lower than either steel or concrete construction.  In view of the marked contrast of the findings of this report with a multitude of published, peer reviewed articles on the same topic, the analysis and related assumptions on which the article is based were closely examined. This review identified significant and multiple flaws in the author’s methodology, including:

• The process for conducting a valid life cycle analysis was ignored.
• Inconsistent methods were used in assessing the different materials compared.
• There are substantial inaccuracies throughout.
• Transparency regarding data sources is lacking.
• Calculation methods on which conclusions are based are not disclosed, and
• The authors relied heavily on non-refereed sources of information.

As an example of the use of inconsistent methods, the approach used in attempting to calculate an overall industry emissions number for the wood products industry was based on U.S. wood products consumption, whereas emissions numbers for steel and concrete were based on U.S. production.  This is but one of many examples of procedural error in the recent report.

Valid comparisons of environmental impacts are made using the strict international protocols for life cycle analysis including requirements for competent review and oversight.  This recent article involved none of the essential elements of such a comparison, and therefore cannot be regarded as a legitimate analysis.

[1]  Bowyer is Professor Emeritus, University of Minnesota Department of Bioproducts and Biosystems  Engineering, and Director of the Responsible Materials Program, Dovetail Partners, Inc. – a nonprofit organization that provides authoritative information about the impacts and trade-offs of environmental decisions, including consumption choices, land use, and policy alternatives.

[2]    Roddy, M. and Serrette, R. 2011. Which Emits the Most CO2 in Home Construction: Steel, Concrete, or Timber?  Think Progress, July 26. (http://thinkprogress.org/romm/2011/07/26/275493/which-emits-the-most-co2-in-home-construction-steel-concrete-or-timber/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+climateprogress%2FlCrX+%28Climate+Progress%29)