This study summarizes the environmental performance of prefinished engineered wood flooring using life-cycle inventory (LCI) analysis. Using primary mill data gathered from manufacturers in the eastern United States and applying the methods found in Consortium for Research on Renewable Industrial Materials (CORRIM) Research Guidelines and International Organization of Standardization (ISO) standard for conducting life-cycle assessments, the environmental impacts in making engineered wood flooring were estimated. This study is a follow-up to the CORRIM Report Module G—Life-Cycle Inventory of Solid Strip Hardwood Flooring in the Eastern United States. Life-cycle impact assessment was beyond the scope of this study.
Engineered wood flooring is designed to be more dimensionally stable than solid strip wood flooring because it is less susceptible to width shrinkage from increases in moisture. Engineered wood flooring as defined by the National Wood Flooring Association consists of several sheets of solid wood (veneer) bonded together with an adhesive under heat and/or pressure. Although plies having 2, 3, 5, 7, or 9 sheets are available, 3 and 5 are most common. Thicknesses can range from 3/8 to 9/16 in. (9.5 to 14.3 mm). Typical manufacturing includes the following eight unit processes: log yard, debarking and bucking, block conditioning, peeling and clipping, veneer drying, lay up, trimming, sanding, sawing and moulding (profiling), and prefinishing. Inputs and outputs to these unit processes were collected from a survey of manufacturers. The multi-unit process approach is the preferred evaluation method because it helps identify possible process improvements by showing the energy and environmental contribution of each unit process.
We determined the environmental impacts based on resource and energy consumption and releases to air, water, and land for making prefinished engineered wood flooring in the eastern United States. Of the five companies contacted in the eastern United States, four companies (comprising four veneer mills and five flooring plants) completed the mill survey. These facilities well represented the industry as a whole, and their manufacturing technology was average. Primary data were collected for the production period January to December 2007. Input data collected included raw materials such as hardwood logs with bark and water, resins, electricity, fossil fuels, prefinishing materials, transportation distances for materials used onsite, and the breakdown of logs into co-products sold (not flooring) such as wood chips and wood fuel burned onsite to produce thermal energy. Allocation of environmental inputs was done on a mass basis because the highest volume product had the highest economic value. This was true for all unit processes. Production unit bases of 1 m3 and 1,000 ft2, were selected to standardize the results to alternative products.
Based on surveyed data from the eastern United States, flooring production of 64,840 m2 (73,270 thousand ft2) was found. This was approximately 19% of the total 2007 engineered wood flooring production in the United States of 346,400 m2 (391,400 thousand ft2). No U.S. wood flooring production data were available by individual states. Surveyed mill production exceeded the minimum CORRIM production data requirement of 5%. In addition, this study met the minimum number of product manufacturers (four). Detailed inputs and outputs of unit processes were collected from these manufacturers and weight-averaged to allow modeling in SimaPro 7.1.8 to estimate emissions to air, water, and land. Results also include a carbon balance of the entire process.
After developing a mass balance from inputs and outputs, an ovendry density of 656 kg/m3 (40.9 lb/ft3) prefinished engineered wood flooring including wood, resins, and finish (coatings) was estimated. Assuming a specific gravity at 6% MC of 0.656, the density was 695 kg/m3 (43.4 lb/ft3). At 0% MC, the largest component of the flooring is wood (578 kg) and represents 88.2% of the final product mass, resins (65 kg) are 9.8%, and the remaining 2.0% finishing material (13 kg). Hardwood plywood and prefinished engineered wood flooring had wood recoveries of 43% and 35%, respectively. These numbers were determined by the output of wood in the form of plywood as a percentage by weight of the wood input to the manufacturing facilities in the log form (white wood only).
Energy consumption and type have significant effects on the environmental performance of all products. In this LCI study, unallocated thermal process energy and electricity consumed was 6,418 MJ/m3 (5.38 million Btu/thousand ft) and 1,113 kWh/m3 (985 kWh/thousand ft2), respectively. Wood fuel at 300 ovendry kg or 6,263 MJ/m3 (5.26 million Btu/thousand ft2) contributed 97.6% of process thermal energy required with the remainder from propane (2.2%) and natural gas (0.2%). Results showed a cumulative allocated value of manufacturing prefinished engineered wood flooring starting with logs at the forest landing to the final product leaving the flooring plant of 22,990 MJ/m3 (19.3 million Btu/thousand ft2) . Unfinished engineered wood flooring showed a cumulative allocated value of 13,600 MJ/m3 (11.4 million Btu/thousand ft2).
Tracking emissions is increasingly important in terms of applying proper emission controls. Two different scenarios were created to track emissions and involved system and onsite boundary conditions. First, the total (cumulative) system boundary covers both onsite and off-site emissions for all material and energy consumed. This includes the fuel resources used for the production of energy and electricity and is part of this LCI. Examples of off-site emissions are grid electricity production, transportation of logs to the mill, and fuels produced off-site but used onsite. The onsite system boundary covers emissions developed just at the prefinished engineered wood flooring facilities (i.e., onsite) from the seven unit processes. Environmental impact outputs from SimaPro were allocated to the production of 1 m3 of prefinished engineered wood flooring. A certain portion of the environmental impacts were assigned to the co-products such as wood chips and were not included in the LCI output for prefinished engineered wood flooring.
Data quality is considered excellent based on the data collected from the manufacturing facilities. We developed detailed surveys (questionnaires) that were reviewed by a CORRIM representative before distribution. In addition, a CORRIM representative reviewed the SimaPro model for this report. Onsite visits to a veneer mill and flooring plant allowed for provides greater insight into the manufacturing process, thus providing higher quality data. The multi-unit process method allows for unit process improvements to be evaluated more precisely than a system process approach.
Modeling data estimated biogenic and fossil CO2 emissions at 623 and 1,049 kg/m3, respectively, and VOCs at 1.04 kg/m3. A cubic meter of prefinished engineered wood flooring stores 1,096-kg CO2 equivalents/m3 as a final product.
The following main conclusions are based on the life-cycle inventory:
• The amount of carbon stored in prefinished engineered wood flooring exceeds the fossil carbon emissions by about 4%. Therefore, as long as prefinished engineered wood flooring and its carbon stay in products held in end uses, the carbon stored will exceed the fossil carbon emitted in manufacturing.
• A trade-off exists between prefinished and unfinished engineered wood flooring. The prefinishing unit process consumes a large amount of electricity from controlling emissions from staining and coating the wood flooring in addition to the prefinishing. As a result, the environmental impact is significantly higher for prefinished engineered wood flooring than for unfinished engineered wood flooring. However, finishing the wood floor after installation in a residential or commercial building (an uncontrolled environment) would result in greater harm to the environment. This harm results from uncontrolled emissions released from the staining and coating process that are now captured or destroyed onsite at the flooring plant.
• Burning fuel for energy generates CO2. Nearly all energy burned onsite for manufacturing prefinished engineered wood flooring comes from woody biomass. Burning biomass for energy does not contribute to increasing atmospheric CO2 provided forests are growing and absorbing the emitted CO2 on a sustainable basis.
• Increasing onsite wood fuel consumption would reduce fossil greenhouse gases but increase other gases, especially particulate emissions. Particulate matter can be captured prior to release to the atmosphere using commercially available technology but not without increased costs and additional inputs such as electricity.