Auantifying Green

Life cycle assessment provides new evidence of woodts green credentials

A LIFE cyclE assessment (LCA) la.project completed recently by the Ontario-based Athena Sustainable Materials Institute provides powerful new evidence for the environmental merits of wood versus concrete.

The analysis compares the environmental footprints of two versions of the same house-one with a raised wood floor, wood walls, and a wood roof, the other with a concrete slab floor system. concrete masonry unit first-story walls, wood-frame second story walls, and a wood roof. Both houses were designed with woodframe interior walls.

The all-wood version was the winning design in the Carbon Challenge 2010 Florida Design Competition, a program sponsored by APA-The Engineered Wood Association in conjunction with the Raised Floor Living program, a cooperative promotion campaign between APA and the Southern Forest Products Association.

Life cycle assessment is now widely recognized as the most scientifically credible and accurate measure of the environmental impacts of various building materials. By quantifying those impacts from "cradle to grave" - extraction, manufacturing , transportation. installation. use, maintenance, and disposal or recyclingLCA provides a common basis for objectively assessing and comparing the environmental credentials of dissimilar building designs and materials.

The Athena analysis encompassed two key end-of-life assessment criteria: emission of greenhouse effect gases that are thought by some to contribute to global warming and fossil fuel consumption. The two house

Fossil Fuel Consumption

designs were modeled in Athena's Impact Estimator software and compared under two end-of-life scenarios. Under the first scenario, the house is demolished and materials are disoosed in a landtill that captures landfill gases and then burns that gas to produce electricity to be put back on the power grid. The second scenario involved demolishing the house and disposing of all non-wood materials in a landfill while burning the wood products directly in order to produce electricity for the srid.

Two secondary data sources-the U.S. Life Cycle Inventory Database (U.S. LCI) and Ecoinvent-were used to model the disposal of materials and their energy recovery at the landfill. (U.S. LCI is a public/private partnership developed by the Department of Energy and the National Renewable Energy Laboratory. Ecoinvent is a life cycle inventory database of the Swiss Ecoinvent Centre, formerly Swiss Center for Life Cycle Inventories.) The material take-off is applicable to a 2,122-sq. ft., two-story house with an assumed minimum life expectancy of 60 years, located in Orlando, Fl.

The charts on pages 28 and 30 show the use of fossil fuels and global warming potential of the wood house design as percentages of the fossil fuel use and global warming potential of the concrete design, under three scenarios: (1) with no advanced end-oflife treatment, (2) with gas-capturing landfill disposal, and (3) with wood combustion. As can be seen, the raised wood floor design yields substantially smaller fossil fuel use and global warming potential rates-and thus a smaller carbon footprint-compared with the concrete design.

The results of the analysis are not surprising in light of all that is commonly known about the environmental merits of wood as a building material. For example:

Wood in forests, particularly in young vigorous forests, absorbs carbon dioxide, making growing forests an efficient carbon sink.

. Once harvested and converted to wood products, wood fiber has a carbon sequestering or storage effect. Sustainably managed forests, as opposed to unmanaged decaying forests, thus provide a net reduction in greenhouse effect carbon dioxide emissions.

. Compared with other materials, wood requires less energy to extract, process, transport, construct and main- taln over ume.

. Wood is a far better insulator than concrete and steel, and can thus reduce energy consumption of buildings during their operational life.

. Wood is both recyclable and divertible from the waste stream to be burned in energy recovering boilers. The energy so produced substitutes for fossil fuel energy, as the Athena analysis shows.

Many of the benefits cited above were confirmed by another Athena Institutc lifc cycle assessment study completed last year. That analysis compared the fossil fuel requirements and greenhouse gas emissions levels of two comparable floor systems-one a concrete slab-on-grade floor, the other a raised wood floor. The assessment covered both cradle-to-sate man- ufacturing effects (from extraction of raw materials to product manufacture to completion of the structure) and cradle-to-grave effects (up to and including structure demolition).

The results of the analysis, which are summarized in APA's "Reducing the Carbon Footprint of Floor Sys/erns," showed that the global warming impacts on a cradle-to-gate basis of the wood floor were less than half that of the concrete slab. Total energy consumption on a cradle-to-gate basis was comparable for the two floor systems. However, the fossil energy requirement for the concrete slab was nearly double that of the wood floor. This is due in large measure to the utilization of biomass energy in the manufacturing of wood products.

The differences in fossil fuel ener- gy consumption and global warming impacts between the two floor systems were shown to be even more dramatic on a full cradle-to-grave basis due to the lower carbon imprint of wood under end-of-life scenarios, as the latest Athena end-of-life analysis demonstrates.

The conclusions of both Athena Institute life cycle assessments have been corroborated by many other LCA studies, including most notably analysis by the Consortium for Research on Renewable Industrial Materials (www.corrim.org).

The latest Athena Institute LCA analysis, which was conducted under contract for APA, is part of a major ongoing initiative by the association to elevate desisn and construction com- munity appreciation of wood's environmental credentials and to safeguard and advance acceptance ofwood products in the growing number of local and national green building standards.

APA, for example, recently completed a series of Carbon Challenge design and construction seminars in Florida as part of its Carbon Challenge program. It has also developed a Green Verification Report service that provides member manufacturers a mechanism for reporting eligibility for points under the National Green Building Standard, International Code Council (ICC) 700-2008, and LEED 2009 for New Construction.

The association also participates in the Research & Technology Committee of the Green Building Strategy Group, an industry initiative formed to coordinate the forest and wood product industry initiatives related to green building. On behalf of the Research Committee, APA last year secured funding from the USDA Forest Products Laboratory to establish a Life Cycle Assessment Working Group, which is comprised of representatives from industry, academia, research organizations, and government.