In this study, NCASI worked with the USDA Forest Service with funding from its Resources Planning Act (RPA) Assessment Program to estimate the effects of using wood-based building materials on national energy use and greenhouse gas emissions. Data developed by the Consortium for Research on Renewable Industrial Materials (CORRIM) were used in an analytical framework that allowed carbon in forests and forest products to be tracked over large areas and long time frames. In addition, NCASI developed a module to follow the fate of carbon in discarded building materials. To ensure that short-term and transient effects did not bias the findings, a time horizon of 100 years was used.

The results indicate that houses with wood-based wall systems required about 15 to 16% less total energy for non-heating/cooling purposes than thermally comparable houses employing alternative steel- or concrete-based building systems. The results for non-renewable energy consumption were essentially the same as those for total energy, reflecting the fact that most of the displaced energy was in fossil fuels. Net greenhouse gas emissions associated with wood-based houses were 20 to 50% lower than those associated with thermally comparable houses employing steel- or concrete-based building systems. Only a small fraction of the building materials need to be changed to accomplish these improvements. In the Atlanta example, the additional wood used in the wood-based house represented only 2.3% of the mass of the house, while in the Minneapolis example, the additional wood used in the wood-based house represented 7.7% of the mass.

On an annual basis, considering 1.5 million housing starts a year, the difference between wood and non-wood building systems is about 9.6 million tonnes of CO2 equivalents per year, and the corresponding energy benefit associated with wood-based building materials is approximately 132 million GJ per year. These figures represent approximately 22% of the embodied energy and 27% of the embodied greenhouse gas emissions in the residential sector of the economy.

The estimates developed in this study were found to be very sensitive to assumptions about carbon accumulation in forests and about the fate of carbon in forests no longer needed for production of wood building materials. Future studies would benefit from a more refined analysis of these issues as well as an analysis of the benefits of producing energy from forest biomass under a variety of scenarios. In addition, the estimates would be improved if data were available for houses representative of regions not included in the CORRIM Phase I work.