WE READ "LIFE-CYCLE REVISITED" IN the January issue of BUILDER to see what we might learn from this new study. We concluded that it "revisited" this complicated subject too briefly to gain the pertinent and balanced facts about life-cycle inventory [LCI] and assessment. The flawed conclusions and suggestions provided by the Consortium for Research on Renewable Industrial Materials appear to be based upon limited, outdated, and seemingly biased information and methodology.
The commentary about house longevity and Athena offered no added credibility or relevance.
The study contains old LCI data on steel making, so the values used are in error. The study appears to skip the end-of-life ramifications for all materials. We see, for example, no credit given for steel recycling at end of life, a very significant omission. There also seems to be no debit allocated to wood framing as it ultimately gives up its earlier carbon credit for "wood product storage" at the end of life of the structure. Whether consumed by fire or released to atmosphere over time as methane emissions, that carbon becomes once again "unsequestered" and should not be ignored. It's also not clear how "forest sequestration" is credited to wood for units used in framing. Perhaps it assumes that every tree harvested is replaced with new growth that beings "sequestering" right away.
In regard to the "... hypothetical homes ... designed to have similar energy efficiency ...," the modeled study would do well to use actual field measurement and analysis. Given proper insulation design and construction, the clear wall energy performance of steel framing can equal or even exceed wood framing.
All materials have environmental impacts in their manufacture or harvest. We suggest that the boundaries of this study were unusual, comparing the purported impacts of manufacturing to construction on the jobsite. It is widely recognized that the embodied energy and emissions from manufacture or harvest are all dwarfed by the ultimate service life usage of energy and other resources, such as HVAC and hot water.
Therefore, when comparing building materials, one should go to a more rigorous LCA methodology, such as the Life Cycle Stressor Effects Assessment (LCSEA) study conducted by Scientific Certification Systems, Oakland, Calif. It concludes that the permanent eco-disruption caused by wood production is about 100 times greater than for steel production in framing an equal number of homes. This gives beneficial credit for optimum forest management practices, including selective harvests, and long turns of 70 years. We suggest your readership would benefit from the LCSEA study described and would be pleased to share it.
GREGORY L. CRAWFORD
VICE PRESIDENT, OPERATIONS
STEEL RECYCLING INSTITUTE