Life cycle impacts of manufacturing redwood decking in Northern California

Awareness of the environmental footprint of building construction and use has led to increasing interest in green building. Defining a green building is an evolving process with life cycle inventory and life cycle impact assessment (LCIA) emerging as key tools in that evolution and definition process. This study used LCIA to determine the environmental footprint associated with manufacturing 38- × 138-mm redwood (Sequoia sempervirens) decking from sustainably managed northern California redwood forests. Primary survey data were collected from four redwood mills that represent 90% of redwood lumber production. The primary data were then weight-averaged on a per-unit basis of 1 m³ of planed redwood decking (380 ovendry kg/m3) to calculate material flows and energy use. All of the raw material consumption and environmental outputs were assigned to dry planed redwood decking and none to coproducts. The gate-to-gate, cumulative energy consumption associated with manufacturing 1 m³ of planed redwood decking from 1.8 m3 of incoming logs was 1.36 GJ/m³ with 19% of the energy provided by burning wood residues. Emission data produced through modeling the production process found that the estimated biomass and fossil CO₂ emissions were 20.9 and 52.9 kg/m³, respectively. Based on the carbon content of redwood of 53%, a cubic meter of 38- × 138-mm redwood decking product stores 201 kg of carbon and if released into the atmosphere would emit 738 kg of CO₂. The amount of carbon stored in redwood decking is equivalent to about 10 times the total CO₂ emissions released during the manufacturing process. Low carbon emissions during the manufacturing process and carbon storage during the service life of a redwood deck are positive environmental attributes that should be considered when selecting a decking product.