Abstract

Goal and scope definition

The goal of the study was to update cradle-to-gate LCI of I-joist manufacturing for the SE and PNW regions of the United States. For this purpose, gate-to-gate LCI of I-joist manufacturing was generated using up-to-date primary data based on 2012 manufacturing. In addition, the cradle-to-gate environmental impacts associated with I-joist production were quantified through LCA using the developed LCI. The two updated LCA data sets will be used to update the current North American I-joist EPD (American Wood Council–Canadian Wood Council 2013).

The scope of the present LCA study covered the cradle-to-gate life-cycle stages of I-joist production, including forest resource activities, OSB, LVL, and FJL production and production of the final I-joist product ready for shipping from the plant. Forest resources were evaluated as a stand-alone life-cycle stage, and thus its impact was captured separately. Transportation of feedstock (i.e., OSB, LVL, FJL, and resins) to the I-joist facility were taken into consideration in the analysis.

Allocation procedure

In this study, allocation of the inputs and environmental impacts associated with the system was necessary because coproducts were generated during the I-joist manufacturing in addition to the main product, I-joist. This article presents the results based on mass allocation where primary energy and environmental outputs were assigned to various coproducts by mass. In addition to mass allocation, economic allocation was performed, and results were presented because product category rules suggest using economic allocation for a multioutput process when the difference in revenues is more than 10 percent, as it was for this study (FPInnovations 2015). Use of economic allocation may help us understand and evaluate the environmental impact of wood residue coproducts based on their economic value rather than considering them a waste material.

Functional unit

A declared unit is used in instances where the function and the reference scenario for the whole life cycle of a wood building product cannot be stated (FPInnovations 2015). In accordance with the PCR developed (FPInnovations 2015), the declared unit for I-joist production was 1 km. All input and output data were allocated to the declared unit of product based on the mass of products and coproducts in accordance with ISO 14044 (ISO 2006b). Use of a linear measurement unit is consistent with industry practice in the United States, where the production is measured in linear feet. Linear measurements are used because it is difficult to quantify I-joist production in other forms, such as volume, owing to its shape. The composite I-joists produced and evaluated in this study conformed to ASTM Standard D5055 (ASTM International 2016) and the APA—The Engineered Wood Association (2015). As the analysis did not take the declared unit to the stage of being an installed building product, no service life was assigned.

System boundaries

The cradle-to-grave system boundaries of the I-joist production system are presented in Figure 1. The system boundary included forest resource management activities, OSB, LVL, and FJL production, and I-joist production life-cycle stages. The transportation of OSB, LVL, and FJL and resins to the I-joist facility was accounted for if production occurred off-site because some facilities perform the FJL and LVL production at the same site. Within the system boundaries, the authors considered the transportation of raw material, the impacts resulting from the supply and generation of the off-site energy sources, and the consumption of ancillary material, such as motor oil, waxes, paint, and hydraulic fluid in the analysis.

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System investigated

Cradle-to-gate LCI flows for composite I-joist manufacturing were presented by five major life stages: forestry operations, OSB production, FJL production, LVL production, and I-joist production.

Inventory approach

The gate-to-gate LCI generated for US I-joist production was based on primary data collected from I-joist manufacturers for the year 2012. I-joist manufacturing LCI data from collected primary data sources were linked to available secondary LCI data. Data for the forestry operations and feedstocks (components) used in I-joist manufacturing, including OSB, FJL, and LVL, come from other CORRIM reports. For FJL LCI, softwood lumber manufacturing data developed by M. R. Milota (M. Puettmann, personal communication, April 24, 2015) were used as feedstock to produce the FJL. The data for OSB and LVL production were from LCI data developed from updating LVL and OSB manufacturing (Kaestner 2015; Bergman and Alanya-Rosenbaum 2017c, 2017d; Puettmann et al. 2016a, 2016b). In addition, forestry operations (Johnson et al. 2005; Puettmann et al. 2013c, 2013d) and finished I-joist packaging LCI data (Puettmann et al. 2013c, 2013d) were retrieved from the literature to construct the cradle-to-gate I-joist plant LCI. Secondary data, such as supply of electricity, natural gas, chemicals, transport, and disposal, were from peer-reviewed literature and the US LCI Database (National Renewable Energy Laboratory [NREL] 2012). Material and energy balances were performed from primary and secondary data to ensure data quality.

Cutoff rules

According to the PCR, if the mass–energy of a flow is less than 1 percent of the cumulative mass–energy of the model flow, it may be excluded, provided that its environmental relevance is minor. This analysis included all energy and mass flows for the primary data collected.

In the primary surveys, manufacturers were asked to report total hazardous air pollutants (HAPs) specific to their wood products manufacturing process regardless of whether they were less than the 1 percent cutoff. If applicable to the wood product, HAPs were reported later in the LCI Data section of Bergman and Alanya-Rosenbaum (2017a, 2017b) and thus are not excluded from this LCI. Under Title III of the Clean Air Act Amendments of 1990, the EPA has designated HAPs that wood products facilities are required to report as surrogates for all HAPs. These are methanol, acetaldehyde, formaldehyde, propionaldehyde (propanal), acrolein, and phenol. All HAPS were included in the LCI; no cutoff rules apply.

Data quality requirements

The present study collected primary data from representative I-joist manufacturers in the United States for two regions: the SE and the PNW. The primary mill data were collected through a survey questionnaire developed to address the production of I-joists. Then, with assistance from the APA, the surveys were mailed to I-joist manufacturing plants. The LCI data were generated based on the survey questionnaire filled out by I-joist manufacturing plants and follow-up calls to complement any missing data along with site visits. A total of two I-joist mills from seven manufacturing facilities completed the questionnaire in the SE region, while three of six provided data in the PNW region. The data represented the average technology of these regions. Total US I-joist production for 2012 was 109 thousand km (358,900 thousand ft) (APA 2014). Three US I-joist plants representing 30.7 percent of 2012 US production (33.6 thousand km [110,346,627 ft]) in the PNW region and two plants representing 27 percent of 2012 US production (29.5 thousand km [96,799,180 ft]) in the SE region participated in the study by providing primary data for the PNW and SE regions. The surveyed plants provided detailed annual production data on their facilities, including on-site energy consumption; transportation data; electricity and natural gas consumption; LVL, OSB, and FJL volumes; and I-joist production. The components of LVL and FJL to produce I-joists were produced in manufacturing facilities in the regions of the United States, while for OSB, US manufacturing of this material is only in the eastern United States. Most I-joist production occurs in conjunction with production of LVL and FJL in either the same engineered wood facility or nearby. For the surveyed mills in this study, all LVL production occurred at the same site as I-joist production and most FJL production as well.

To ensure data of the highest quality, data control measures were taken. Quantitative mass balances were performed to verify data quality. First, mass balances at individual facilities were conducted where the data were found to be consistent for the surveyed mills. Second, overall wood mass in and total wood mass out for both regions were calculated, and the difference was less than 2 percent. A difference less than 10 percent is considered good for wood product production. In addition, the primary data obtained from the surveys were analyzed using the weighted-average approach. The weighted coefficient of variation representing the variability in the collected process data was calculated and presented. Additionally, a sensitivity analysis investigating the energy inputs into I-joist production was performed to investigate the robustness of the impact assessment results.

Assumptions and limitations

The data collection, analysis, and assumptions followed the protocol defined by CORRIM in ‘‘Research Guidelines for Life-Cycle Inventories'' (2014). To conform to ISO 14040 (ISO 2006b), additional considerations are listed below:

• All flow analyses of wood and bark in the process were determined on an ovendry weight basis using a weighted-average green specific gravity of 0.55.

• Although small in quantity relative to the wood mass, impacts from the production of the resin system were included in the analysis.

• Because of the small consumption values for sodium hydroxide, catalyst, and melamine components of the resin system, no transportation data were provided or incorporated into the analysis.

• Data collected from the participating facilities were analyzed using a weighted-average approach to develop a “composite” I-joist production facility. Where appropriate, missing data from facilities were not included in the weight averages. Inconsistent data were addressed by contacting facility personnel to solve the discrepancy.

• The authors did not collect 2012 primary regional forest resource data but used secondary data from earlier LCA studies to develop the cradle-to-gate analysis. It is expected that forest resource data will be updated in the near future. As mentioned previously, to develop new EPDs, new underlying LCA data must be continually generated per the North American wood product PCR (FPInnovations 2015).

• For regional forest harvesting, a single estimate of the average volume harvested per unit area was developed by weighting three combinations of management intensity (low, medium, and high intensity) and site productivity based on the relative percentage of the land base they occupy. Puettmann et al. (2013c, 2013d) list specific inputs, input assumptions, variations in harvest equipment, and fuel consumptions for the three management intensities for the two regions.

• Harvesting cycles averaged 27 and 45 years for the SE and PNW, respectively.

• Land use impacts, including biodiversity and biotic resource depletion, were not incorporated into the present study. The forests were considered to be replanted as forests and eventually returned to their previous state through forest management sustainability practices. Ecological impacts from harvesting forest resources are best covered by forest sustainable certification programs; thus, their impacts affecting plant and wildlife diversity, water quality, and other similar factors were not considered.

• Forest carbon increases and decreases were not tracked, but the authors considered that the harvested trees were being sustainably managed through the ASTM standards D7612‐10 and D7480‐08 (ASTM International 2010, 2014b). Additionally, sustainably managed forests are virtually carbon neutral (Lippke et al. 2011).

• Temporal dimensions of greenhouse gas (GHG) emissions were not included because the study focused on the cradle-to-gate production, which occurs within a relatively short time frame, versus cradle-to-grave production, where long-term GHG emissions and carbon sinks have a greater influence on the global warming (GW) impact category (Bergman 2012).

• OSB was not manufactured in the PNW. The OSB manufacturing LCI data from Puettmann et al. (2016a; personal communication, April 24, 2015) were used for both the SE and PNW regions.

• A mass balance was performed to verify data quality. A difference less than 10 percent was considered good for wood product manufacturing facilities.

• Biogenic CO₂ emissions were tracked and reported, but the TRACI impact method does not count the contribution of wood-derived CO₂ emissions from burning wood fuel in the boiler toward the GW impact estimate (Bare 2011).

• Carbon content for wood products is assumed to be 50 percent by mass of ovendried wood.

• MUF resin was used as proxy for melamine-formaldehyde resin, which is used in the FJL production life-cycle stage.

Impact category method

The life-cycle impact assessment (LCIA) was performed using the TRACI 2 method (Bare 2011). Five impact categories were examined, including global warming potential (GWP [kg CO₂ eq]), acidification (kg SO₂ eq), eutrophication (kg N eq), ozone depletion (kg chlorofluorocarbons-11 eq), and photochemical smog (kg O₃ eq). The five impact categories evaluated in this study were in line with the requirement of the wood products PCR (FPInnovations 2015).

Sensitivity analysis

Sensitivity analysis is commonly used in the LCA to determine the effect of variations in assumptions, methods, and data on the results of the analysis. It allows identification of sensitive parameters that require high accuracy in order to improve the quality of the analysis. In this study, a sensitivity analysis was performed by investigating the impact of the variation of on-site energy consumption (i.e., natural gas and electricity) at the I-joist production life-cycle stage to the overall cradle-to-gate output. Sensitivity analysis was completed per ISO 14040 and 14044 standards (ISO 2006b, 2006c).

LCI analysis

Table 1 provides the detailed data on the material inputs of the gate-to-gate I-joist production stage. Under materials, wood feedstocks included OSB, LVL, and FJL. The weighted production coefficient of variation (CoVw) values were calculated for system inputs and outputs to investigate data consistency where the product (I-joist) data showed high consistency between facilities, with a CoVw of 4.6 and 2.2 percent for the SE and PNW, respectively. The CoVw for total feedstock input was 7.5 percent (SE) and 4.7 percent (PNW).

Table 1 Gate-to-gate material flow analysis of 1 km of I-joist manufacturing in the Southeast (SE) and Pacific Northwest (PNW) regions.

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The CoVw values of the I-joist manufacturing site energy inputs are presented in Table 2. Electricity and natural gas were the primary energy inputs in both regions, where both showed large variation. Although the input wood raw material has a high energy potential, the feedstock energy of the wood raw material was not included as an energy input because this wood was not used as an energy source in the system investigated. The feedstock energy in the wood leaves the system still embodied in the product and coproducts, as shown in Table 1.

Table 2 Gate-to-gate weighted-average on-site energy inputs to produce 1 km of I-joist.

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Air emissions were derived from the data received from the surveyed mills along with pertinent emissions data categorized by the USEPA (2002). Most of the air emission data were the on-site air emissions reported by the surveyed I-joist manufacturers, while the acetone emissions were augmented by a secondary data source (Table 3; US EPA 2002). The main emission sources were from hot presses. Baghouses were the primary collectors of particulate matter (PM), with all surveyed plants using the emission control device (ECD; US EPA 2003a). To reduce volatile organic compound (VOC) emissions from dryers, plants reported the use of regenerative thermal oxidizers (RCOs), sometimes referred to as regenerative thermal oxidizers (RTOs), and wet scrubbers (US EPA 2003b). Thermal oxidizers are typically fueled by natural gas. RCOs are designed to destroy VOCs and other emissions, including PM and soot (US EPA 2003c).

Table 3 Direct outputs reported from production of 1 km of I-joist, gate to gate.^a

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Based on mill surveys, the weighted-average one-way haul distance for feedstock along with the components of the resin system are provided in Table 4. The zero values for LVL shipping distances in the PNW represent the LVL produced concurrently at the I-joist production site. All upstream transportation of inputs to LVL, FJL, and OSB production were included in the respective LCI input values.

Table 4 Weighted-average delivery distance (one-way) by mode for materials to I-joist plant.^a

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Cumulative energy consumption

The cumulative primary energy consumption (CPEC) for the cradle-to-gate production of SE and PNW I-joists is provided in Tables 5 and 6, respectively. The LVL stage was responsible for the majority of the primary energy consumption with 55 and 51 percent for the SE and PNW, respectively. This was due to high natural gas and wood fuel consumption, where the wood and natural gas were used to generate thermal energy for log conditioning and for drying and pressing veneers at the LVL stage.

Table 5 Cumulative primary energy consumption per 1 km of cradle-to-gate I-joist in the Southeast region (mass allocation).^a

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Table 6 Cumulative primary energy consumption per 1 km of cradle-to-gate I-joist in the Pacific Northwest region (mass allocation).^a

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Total energy use at the I-joist production stage was dominated by fossil fuels, where the greatest contributor was natural gas followed by coal and crude oil. At the I-joist life-cycle production stage, natural gas was used to generate thermal energy for resin curing and emission control (e.g., thermal oxidizers), and electricity was consumed for sawing, trimming, resin curing (e.g., the radio-frequency ovens), and emission control (e.g., RCOs).

Life-cycle impact assessment

In this study, five midpoint impact categories were investigated. Environmental performance results for five impact categories along with energy consumption from nonrenewable fossil and nuclear fuels, renewables (wind, hydroelectric, solar, geothermal), renewable and nonrenewable resource use, and solid waste generated are presented in Tables 7 and 8 for the SE and PNW, regions, respectively. Overall cradle-to-gate primary energy consumption was 82.0 and 74.2 GJ/km for all five life-cycle stages in the SE and PNW, respectively. Solid waste generated through the life cycle was dominated by the LVL stage followed by I-joist and OSB production stages. Solid emissions include ash generated at the wood boiler during veneer production for LVL production, and primarily fuels and resins used.

Table 7 Environmental performance of 1 km of I-joist, cradle to gate, Southeast region (mass allocation).^a

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Table 8 Environmental performance of 1 km of I-joist, cradle to gate, Pacific Northwest region (mass allocation).^a

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In addition, the contribution of life-cycle stages to the overall impact for eutrophication, acidification, smog, and GW impact categories are provided in Figure 2. The GW impact category was dominated by LVL production, followed by OSB and I-joist manufacturing stages; the major contributors at the I-joist stage production were electricity use in both regions (37% and 35% in SE and PNW, respectively), followed by natural gas use (21%) in the SE and transportation (34%) in the PNW. The contribution of the LVL production stage to GW was about 42 and 55 percent for the SE and PNW, respectively. The I-joist production stage had a notable contribution at two impact categories investigated owing to PRF resin consumption: ozone depletion and eutrophication. Forest operations had a minor contribution to the overall impact in both regions.

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Scenario analysis

In this study, both mass and economic allocations were performed to investigate the influence of the allocation method on the resulting impact. The contribution of five life-cycle stages to the LCA results for mass and economic allocation are provided in Tables 9 and 10 for the SE and PNW, respectively. Applying economic allocation resulted in increased impact of the I-joist production stage compared with mass allocation because of the low value of the coproducts generated at this stage. Overall, the change in contribution of different life-cycle stages to various impact categories was minor when economic allocation was used.

Table 9 Environmental impact assessment results for mass and economic allocation for the Southeast region.^a

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Table 10 Environmental impact assessment results for mass and economic allocation for the Pacific Northwest region.^a

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Comparison

The on-site, industry-average energy consumption at the I-joist production plant was compared with a previous CORRIM Phase I study that developed LCI for US I-joist production based on 2000 data (Wilson and Dancer 2005a; Puettmann et al. 2013c, 2013d). In particular, the natural gas consumption reported in 2012 was substantially higher compared with the Phase I study in both regions (Tables 11 and 12). In addition, diesel consumption in the SE and PNW and propane consumption in the PNW, which were relatively small inputs, showed a high variation. In particular for the SE, natural gas consumption drove the total impact from energy with a change of 587 percent (Table 11). As expected from the higher CPEC value found earlier, the on-site energy inputs were substantially higher than for Phase I for the PNW as well (Wilson and Dancer 2005a; Puettmann et al. 2013c, 2013d). As for the PNW, electricity, along with natural gas consumption, drove the total impact from energy with changes of 37 and 7,820 percent, respectively (Table 12). Therefore, a sensitivity analysis was conducted to investigate the energy inputs into I-joist production to see their overall impact. However, the apparent statistical differences between the older and current studies could not be adequately addressed because no statistical description of the data from the earlier study was available. The earlier CORRIM study did not perform sensitivity analysis. However, there was sufficient reason to attempt to quantify the energy impacts associated with I-joist production.

Table 11 Production weighted-average Southeast region on-site energy inputs for manufacturing 1 km of I-joist.

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Table 12 Production weighted-average Pacific Northwest region on-site energy inputs for manufacturing 1 km of I-joist.

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The CO₂ emissions released during the forest operations; the manufacturing of the three components OSB, FJL, and LV-L; and the final product, I-joist, and carbon stored in the product are provided in Table 13 minus the weight of the resin. Based on carbon stage calculation, 1 km of I-joist stores 7,285 and 7,255 kg CO₂ eq¹ for the SE and PNW, respectively, where the carbon storage in the final product was about three times more than the carbon emissions that occurred during its production. This result supported the amount of carbon emission savings showed by Bergman and et al. (2014) when replacing a steel I-joist with a comparable composite wood I-joist along with the importance of carbon being stored in wood (Lippke et al. 2010).

Table 13 Carbon balance per kilometer of I-joist.

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Sensitivity analysis

A sensitivity analysis was performed in accordance with the ISO 14040 standard to model the cradle-to-gate effects of varying on-site natural gas consumption and electricity consumption during I-joist production. Neither natural gas nor electrical consumption on-site had a substantial impact on the overall process because on-site I-joist production CPEC contributed only roughly 13 and 16 percent of the energy impacts of cradle-to-gate I-joist production in the SE and PNW, respectively.