Life cycle assessment of borate-treated lumber with comparison to galvanized steel framing

Abstract

A cradle-to-grave life cycle assessment was done to identify the environmental impacts related to borate-treated lumber used as structural framing and to determine how the impacts compare to the primary alternative product, galvanized steel framing members. Borate-treated lumber may be used for framing buildings in locations of high decay or termite hazard. A model of borate-treated lumber life cycle stages was created and used to calculate inputs and outputs during the lumber production, treating, use, and disposal stages. Lumber production data are based on published sources. Primary wood preservative treatment data were obtained by surveying wood treatment facilities in the United States. Product use and disposal inventory data are based on published data and professional judgment. Life cycle inputs, outputs, and impact indicators for borate-treated lumber were quantified using life cycle assessment LCA methodologies at functional units of 1000 board feet, 100 linear feet (30.5 linear meters) of structural perimeter wall framing, and framing required for the perimeter walls of one representative home. In a similar manner, a life cycle inventory model was developed for the manufacture, use, and disposal of the primary alternative product, galvanized steel framing, and comparisons were done using an equivalent measure of 100 linear feet of structural perimeter wall framing. Impact indicator values such as greenhouse gas (GHG) emissions, fossil fuel use, water use, acidification, ecological toxicity, smog forming potential, and eutrophication were quantified for each of the two framing products.National normalization was done to compare the significance of the framing in a representative U.S. family home to the family’s total annual impact footprint. If a U.S. family of three builds a 2225 square feet (207 square meters) home using borate-treated lumber for structural perimeter wall framing, the framing impact “footprint” (normalized over the use life of the structure) for GHG emissions, fossil fuel use, acidification, ecological toxicity, smog forming potential, and eutrophication each is less than one-tenth of a percent of the family’s annual overall impact. The cradle-to-grave life cycle impacts of borate-treated lumber framing were approximately four times less for fossil fuel use, 1.8 times less for GHGs, 83 times less for water use, 3.5 times less for acidification, 2.5 times less for ecological impact, 2.8 times less for smog formation, and 3.3 times less for eutrophication than those for galvanized steel framing.