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LIFE CYCLE ENERGY AND ENVIRONMENTAL IMPACTS OF CROSS LAMINATED TIMBER MADE WITH COASTAL DOUGLAS-FIR

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In this study, a cradle-to-gate life-cycle assessment (LCA) of Oregon-made cross-laminated timber (CLT) was conducted as per the ISO guidelines. Primary data pertaining to CLT manufacturing was collected from a production facility in Oregon and modeled with existing LCA data of Pacific Northwest softwood lumber production and harvesting operations. Primary energy is reported and encompasses all processes within the system boundary. Carbon emissions are reported and include fossil-based emissions from transportation and all production processes and carbon storage in CLT. LCA results are presented for five impact categories, primary energy consumption, and net carbon impact of CLT. Results show the environmental advantage of CLT due to storing of large amounts of biogenic carbon in a building structure for a lifetime. The amount of carbon stored in CLT offsets the emissions released from all production processes; this indicates that CLT is a net negative carbon emitter, as more carbon is stored in the product than is emitted to produce the product. This study shows the importance of using the LCA methodology for showing the net amount and type of energy used for production and the potential climatic impacts of using wood products. This LCA study makes no comparative assertions.
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RESEARCH
Journal of Green Building 17
LIFE CYCLE ENERGY AND ENVIRONMENTAL
IMPACTS OF CROSS LAMINATED TIMBER
MADE WITH COASTAL DOUGLAS-FIR
Maureen Puettmann, PhD.,1 Arijit Sinha, Associate Professor,2
Indroneil Ganguly, Assistant Professor3
ABSTRACT
In this study, a cradle-to-gate life-cycle assessment (LCA) of Oregon-made cross-lam-
inated timber (CLT) was conducted as per the ISO guidelines. Primary data pertain-
ing to CLT manufacturing was collected from a production facility in Oregon and
modeled with existing LCA data of Pacic Northwest softwood lumber production
and harvesting operations. Primary energy is reported and encompasses all processes
within the system boundary. Carbon emissions are reported and include fossil-based
emissions from transportation and all production processes and carbon storage in
CLT. LCA results are presented for ve impact categories, primary energy consump-
tion, and net carbon impact of CLT. Results show the environmental advantage of
CLT due to storing of large amounts of biogenic carbon in a building structure for a
lifetime. e amount of carbon stored in CLT osets the emissions released from all
production processes; this indicates that CLT is a net negative carbon emitter, as more
carbon is stored in the product than is emitted to produce the product. is study
shows the importance of using the LCA methodology for showing the net amount
and type of energy used for production and the potential climatic impacts of using
wood products. is LCA study makes no comparative assertions.
KEYWORDS
life-cycle assessment, CLT, energy, carbon impacts, cradle-to-gate
INTRODUCTION
Sustainability of resources and environmental impacts for extraction and production are becom-
ing important considerations when deciding on a suitable structural material for a building
or infrastructure project (Sinha et al. 2013). Since the environmental impacts and benets of
wood use have been well documented over the base decade (Bergman and Alanya-Rosebaum
2017a; Bergman and Alanya-Rosebaum 2017b; Bowers et al. 2017; Milota and Puettmann
2017; Milaj et al. 2017; Oneil and Puettmann, 2017, Salazar and Meil 2009), it has become
1. WoodLife Environmental Consultants, Corvallis, OR. maureen.puettmann@woodlifeconsulting.com
2. Dept. of Wood Science and Engineering, Oregon State University, Corvallis, OR. arijit.sinha@oregonstate.edu
3. Center for International Trade in Forest Products, School of Environmental and Forest Sciences, University of Washington, Seattle, WA.
indro@uw.edu
18 Volume 14, Number 4
a material of choice for building structures with an enhanced sustainability goal. Wood-based
materials have been shown to outperform steel and concrete assemblies over several impact
categories, including energy and solid waste. Perez-Garcia et al. (2005) reported that wood
oor assemblies used 67% less energy and 157% less carbon emissions, and 312% less water
consumption from cradle to grave than an equivalent steel assembly.
Building construction and use contributes almost 40% of United States (U.S. carbon
dioxide (CO2) emissions and about 41% of total U.S. energy consumption (DOE 2010).
Building operations is the main contributor, along with building material and construction
practices (Dixit et al. 2010). Although wood is the primary building material in single-family,
residential construction, however, there is limited application in mid-rise and commercial build-
ings. With the introduction of mass timber products, specically cross laminated timber (CLT)
the dynamics of the building industry is changing.
Cross-laminated timber is leading the mass timber movement, which is enabling design-
ers, engineers, and other stakeholders to build taller wood buildings. It is a mass timber panel
made by laminating dimension lumber orthogonally in alternating layers. CLT has many envi-
ronmental advantages as a natural carbon store and that its use generates virtually no waste at a
building site, as panels are generally prefabricated before delivery. CLT panels are lightweight,
yet very strong, with good re, seismic, and thermal performance. e recently completed
Brock Commons building in Vancouver, British Columbia, is only one of many testimonies to
the gaining momentum of the mass timber movement. e perceived benet of using CLT as
compared to other building materials because of its superior environmental performance can
be validated by using the robust life-cycle assessment (LCA) methodology. LCA is the best tool
for determining energy use and the potential climatic impacts of buildings with CLT.
LCAs of wood buildings have shown that these buildings have a negative carbon footprint.
A negative carbon footprint occurs when the nal use product stores more carbon than is emitted
through the production and use processes. For a standard wood-frame structure, Gustavasson
et al. (2010) reported a net emissions of –62 kg CO2 equivalent per square meter (eq./m2) for
the entire life cycle of a building (50 years). When the life cycle is pushed out to 100 years, the
net building carbon emissions is 251 kg CO2 eq/m2, with the increase coming from operational
(heating and cooling) impacts. Wallhagen et al. (2011) reported that substituting reinforced
concrete slabs with laminated wood reduced the impact by 25%. When carbon sequestration is
accounted for, a CLT building system has the potential to have greater negative impacts than a
standard wood-framed building and a much higher environmental advantage over non-renew-
able materials, especially in the Pacic Northwest (PNW) where designing for seismic standards
can be signicant in material use. In cradle-to-gate assessments of Canadian CLT (Structurlam
2013), net carbon impacts have been reported at –678 kg CO2 eq/m3 (estimated –99 kg CO2
eq./m2), which can position CLT with a high environmental advantage over non-wood materials.
In Canada, the LCA conducted by Robertson et al. (2012) comparing a CLT building
to a traditional reinforced-concrete building showed that wood was advantageous in 11 out of
12 impact categories, with a global warming potential (GWP, kg CO2 eq.) reduction of 71%.
Since primary data on the manufacturing of CLT and impacts associated with them was not
captured at the time of the particular study, Robertson et al. (2012) assumed that the production
of glue-laminated beams was applicable to CLT production on a volume basis. is is a major
drawback of the study, and it emphasizes the need to obtain primary data on CLT production
and use. In the absence of primary data on CLT, any comparison using LCA that is based on
certain assumptions will have limited scope and may be subject to criticism. Consequently, there
Journal of Green Building 19
is a pressing need to collect primary data on CLT manufactured in the U.S. and to conduct an
LCA of the product. At the time of this writing, there were only two certied structural CLT
manufacturer in the U.S.—one in Oregon and the other in Montana. e Oregon manufacturer
is the rst plant established in the U.S. that produces certied CLT panels and is amongst the
largest; an LCA of their product line has been conducted and the results are presented herein.
When this LCA was conducted, the certied panels produced from the Oregon CLT manufac-
turing facility were solely composed of coastal Douglas-r laminating stock (lamstock).
USE OF CLT IN BUILDING STRUCTURES
CLT can be utilized within a building as a gravity system for above-grade applications, as well
as for lateral systems like shear walls (Figure 1). Predominantly, CLT is used along with other
traditional materials, in a variety of building construction applications and thus, resulting in a
hybrid construction. e Brock Commons building in Vancouver, Canada, is a good example
of a hybrid system, with a concrete lateral force resisting core and wooden gravity system. Using
a wide range of design parameters, a “hybrid CLT building” study estimated the potential use
of CLT in various applications for mid-to-high rise buildings (Ganguly et al. 2017). e model
provided estimates for the bill of materials for a gravity system of a hybrid CLT building. In a
hybrid CLT building, concrete and rebar can be replaced with CLT in slab applications (hori-
zontal diaphragms) using a direct substitution approach and with glulam beams substituted for
the columns. In most cases, CLT would be used in conjunction with other traditional materials.
For example, CLT and concrete composite oors were installed in the John W. Olver Design
Building at the University of Massachusetts, Amherst (UMass Amherst 2018). e nal volume
of CLT used in a building would depend on end-use specic material substitution and the
regional building code restrictions (Karacabeyli et al. 2013; Ganguly et al. 2017).
ENVIRONMENTAL STANDARDS
ere are standards in place for conducting LCAs. e International Organization for
Standardization published requirements and guidelines for conducting LCAs (ISO 2006a).
Lifecycle assessments conducted solely under the ISO standard might not necessarily report on
FIGURE 1. CLT used in various application. CLT as a floor assembly with concrete and CLT
and glulam wall assemblies, John W. Olver Design Building at the University of Massachusetts,
Amherst. Photo credit Alex Schreyer (Left). A CLT wall component being installed, Peavy Hall,
Oregon State University (Right). Photo credit Arijit Sinha.
20 Volume 14, Number 4
the same functional unit or even report the same impacts. Product Category Rules (PCR) make
it easy to consistently evaluate environment impacts of products and facilitate comparisons. A
PCR is a set of rules, requirements, and guidelines following international established protocols
to develop environmental product declarations (EPD) (ISO 2006a 2006b). e users of a PCR
can be manufacturers of wood products, architects, builders, and other interested parties. A
PCR presents a structure that is intended to ensure a harmonious approach to derive, verify,
and present EPDs for solid wood building products in North America.
An EPD is a document that provides, in a user-friendly format, the environmental impacts,
energy usage, and other information that results from a science-based LCA of a product. EPD
development is based on a set of international standards (ISO 2006a, 2006b) outlined in the
PCR that denes the processes to be used when evaluating some or all of the product's life-
cycle stages. An EPD provides the basis for an evaluation of the environmental performance of
products but does not "judge" whether the product or service meets any environmental quality
standard. Users of EPDs are able to make their own judgments based on the information
presented. Most importantly, perhaps, an EPD is a disclosure by a company or industry that
makes public the standardized environmental impacts of its products. While an EPD would not
include comparisons between products or make reference to any environmental benchmark or
baseline, when properly structured and veried against the same PCR, an EPD for one product
can be used for comparison against the EPD for another. e key is that for realistic comparisons
the functional unit must be the same.
METHODS
Life Cycle Assessment
Life-cycle assessment is an internationally accepted method to analyze complex impacts and
outputs of a product or process and the corresponding eects they might have on the environ-
ment. LCA is an objective process to evaluate a product’s life cycle by identifying and quantify-
ing energy and materials used and wastes released to the environment; to assess the impact of
those energy and materials uses and releases on the environment; and to evaluate and implement
opportunities to eect environmental improvements. More details about the LCA methodolo-
gies and standard can be found in Milota and Puettmann (2017) and Oneil and Puettmann
(2017), where the reader is directed for more background. is study can be categorized as a
cradle-to-gate LCA, as it includes forestry operations using sound-secondary analysis though
the manufacturing of CLT ready to be shipped at the mill gate.
Scope
e scope of this study was to develop a cradle-to-gate LCA of CLT using upstream processes
for wood production common to practices and technology specic to the Pacic Northwest
U.S. e LCA of CLT includes the impact in terms of material ow, energy type and use, emis-
sions to air and water, solid waste production, and water impacts for the CLT process on a per
unit volume basis of 1.0 cubic meter (m3). Data for the LCA are based on gate-to-gate inputs
and outputs obtained directly from the manufacturer; recently published data for gate-to-gate
softwood lumber production (Milota and Puettmann 2017) and cradle-to-gate forest resources
LCI’s (Oneil and Puettmann 2017) were used for the upstream process inputs for CLT produc-
tion. is is a commonly accepted process in mainstream LCA where a mix of secondary and
primary data is used for analysis.
Journal of Green Building 21
All input and output data were allocated to the declared unit of product based on the mass
of products and co-products in accordance with standards for conducting LCAs (ISO 2006a),
which makes this a cradle to CLT manufacturing gate LCA with no service life assigned to the
CLT. e declared unit for CLT is 1.0 m3 (or 35.3 ft3). 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. All input and output data were allocated to the declared unit of product, based
on the mass or economic basis of products and co-products in accordance with ISO protocol
(ISO 2006a) and the PCR (FPInnovations 2015) for future EPD development. is analysis
does not take the declared unit to the stage of being an installed building, so no service life is
included in the results.
System Boundaries
e system boundary begins with regeneration in the forest and ends with the CLT product
at the gate of the CLT production facility (Figure 2). e system boundary includes forest
operations, which may include site preparation and planting seedlings, fertilization and thin-
ning, pesticide and or herbicide use, and nal harvest with the transportation of logs to the
lumber production facility, transportation of lumber to CLT manufacturing site, and onsite
production of CLT. e CLT production complex was modeled as a single unit process. e
study recognized ve steps necessary to make CLT. Excluded from the system boundaries are
xed capital equipment and facilities, transportation of employees, land use, delivery of CLT
to construction site, construction, maintenance, use, and nal disposal.
FIGURE 2. System boundary for cradle-to-gate CLT manufacturing.
22 Volume 14, Number 4
Allocation Method
Cross laminated timber is the main product in the manufacturing process. We used two alloca-
tion approaches: 1. mass allocation and 2. economic allocation. A mass allocation is the most
common allocation approach and measured with high accuracy. Mass allocation also allowed for
the comparison with equivalent building materials in design assemblies. On a mass basis, 83%
of the input wood material is applied to the CLT product. We also used an economic allocation
to stay within conformance of the PCR in case an EPD was later to be developed for Oregon
CLT. For the economic allocation we assumed that of the CLT product had a value greater
than 10 times the value of the coproducts (shavings, waste, o specs and end cuts) therefore,
no allocation was assigned to the coproducts allowing 100% of the impacts allocated to CLT.
Impact Assessment
e life-cycle impact assessment (LCIA) phase establishes links between the life-cycle inven-
tory results and potential environmental impacts. e LCIA calculates impact indicators, such
as global warming potential and smog. ese impact indicators provide general, but quanti-
able, indications of potential environmental impacts. e target impact indicator, the impact
category, and means of characterizing the impacts are summarized in Table 1. Environmental
impacts are determined using the Tool for Reduction and Assessment of Chemical and Other
Environmental Impacts (TRACI) method (Bare 2011). ese ve impact categories reported
are consistent with the requirements of the wood products PCR (FPInnovations 2015), which
are requirements for a product environmental declaration.
Each impact indicator is a measure of an aspect of a potential impact. is LCIA does not
make value judgments about the impact indicators, meaning comparison indicator values are
not valid. Additionally, each impact indicator value is stated in units that are not comparable
to others. For the same reasons, indicators should not be combined or added.
e cumulative energy demand (CED) impact method was used for summarizing primary
energy (coal, oil, natural gas, nuclear, biomass, hydro, and other renewables). e primary
fuels were further categorized into non-renewable fossil, non-renewable nuclear, renewable
woody biomass, and other renewables (hydroelectric, wind, solar, geothermal). e CED impact
method was adjusted to include the mill residues used for heat energy in the western softwood
lumber model. Table 1 summarizes the source and scope of each impact category reported.
Consideration of Biogenic Carbon
e forest products industry is consistently challenged regarding its environmental sustainabil-
ity. e greatest challenges with respect to practices center on the extraction of forest resources,
with questions about carbon stores and ows in the forest environment. Carbon dioxide is
considered the primary contributor to the rise in global temperatures and is released from the
combustion of fossil and biomass fuels.
e appropriate methodology for assessing the impacts of CO2 releases and other green-
house gases is GWP, which compares the amount of heat trapped by a certain mass of the gas
in question to the amount heat trapped by a similar mass of CO2. GWP is an indicator that
reects the relative eect of a greenhouse gas in terms of climate change, considering a xed
time-period, commonly 20, 100, or 500 years. For example, the 20-year GWP of methane is
56, which means if the same weights of methane and CO2 were introduced into the atmosphere,
methane would trap 56 times more heat than the CO2 over the next 20 years.
Journal of Green Building 23
Standards such as ASTM D7612 (2015), which are used in North America to dene
legal, responsible, and/or certied sources of wood materials, are in place to provide assurances
regarding forest regeneration and sustainable harvest rates that serve as proxies to ensure stable
carbon balances in the forest sector. ey are outside the accounting framework for this LCA.
Forest Resources Inputs
e wood extraction stage provides estimates of the yield and emissions associated with the man-
agement of representative timber-producing acres for the area west of the Cascade Mountains
in Washington and Oregon, in what is commonly called the PNW Douglas-r region. Data for
resource extraction was based on the cradle-to-gate LCA by Oneil and Puettmann (2017) and
adjusted where necessary to represent only Douglas-r. is region is dominated by temperate
coniferous rainforests comprised mainly of Douglas-r (Pseudotsuga menziesii) and western
hemlock (Tsuga heterophylla), with other species such as spruce (Picea spp.), true rs (Abies ssp.)
and western redcedar (uja plicata) making up a smaller component of the harvested softwood
volume. Only the harvest of Douglas-r timber was considered in the LCA on CLT. Harvests
were predominately from large private and industrial landowners (Oneil and Puettmann 2017).
e gate-to-gate process for PNW forest operations considers landscape-level impacts. e
potential impacts to soil carbon and biodiversity are outside the scope of this analysis. Under a
mass allocation approach, roundwood harvested and delivered from the roadside was 1.09 m3/
m3 of CLT (1.86 m3/m3 using an economic allocation).
Lumber Inputs
Douglas-r kiln-dried rough saw lumber is the wood input for CLT. Lumber is produced in
Oregon following processes outlined by Milota and Puettmann (2017). Rough dry lumber is
TABLE 1. Impact category sources and scope.
Impact category Unit Method Level of site specificity
Global warming kg CO2 eq TRACI 2.1 v1.01 Global
Smog kg SO2 eq TRACI 2.1 v1.01 North America
Acidication kg N eq TRACI 2.1 v1.01 North America
Ozone depletion kg CFC-11 eq TRACI 2.1 v1.01 North America
Eutrophication kg O3 eq TRACI 2.1 v1.01 North America
Tota l e n e r g y MJ CED Global
Non-renewable fossil MJ CED Global
Non-renewable nuclear MJ CED Global
Renewable woody biomass MJ CED—modied Global
Other renewables*MJ CED Global
* solar, wind, hydro, geothermal
24 Volume 14, Number 4
delivered by truck from the supplier to the CLT facility. e weighted average amount of wood
only in a CLT panel is 537 kg/m3, requiring a total of 649 kg of oven-dry rough lumber or 1.21
m3 for both product and coproducts produced. For mass allocation, only 83% of the 649 kg
of lumber input is assigned to CLT. However, in the case of an economic allocation 100% of
the lumber input is assigned to CLT.
CLT Production
Cross-laminated timber is a multi-layered structural wood product constructed of large panels
made from solid wood and glued together in alternating directions of their bers. CLT panels
consist of an odd number of layers (usually three to seven) and may be sanded or prenished
before shipping. While at the mill, CLT panels are cut to size, including door and window
openings, with state-of-the art computer numerical controlled (CNC) routers capable of making
complex cuts with high precision.
e Oregon CLT facility used for this study is located in southern Oregon along the
Interstate 5 corridor. Oregon CLT is manufactured with Douglas-r lumber in accordance with
the V1 or custom grade of ANSI/APA PRG 320 (2018). CLT panels can be used in oor, roof,
and wall applications and are manufactured with nominal widths of 0.305–3.05 m (1–10 ft),
thicknesses of 10.48–24.45 cm (4-1/8 to 9-5/8 inches), and lengths of up to 12 m (42 ft). e
CLT produced in this facility is certied by the American Panel Association (APA).
Cross-laminated timber is produced from 2×4-12, #2 and #3 or MSR graded lumber
dried to 12% (+/– 3%) moisture content. e production begins with the lumber entering a
sorting line where it is planed to 1-3/8 inch. e lumber is then sorted by grade and moisture
content. e lumber is then vertically nger jointed using a melamine-based resin and cured
using a radio frequency dryer. After a nal quality check, the nger-jointed lumber is moved
to assembly trays. Assembly of a 3-layer CLT panel would include higher-quality lumber pieces
placed as a rst layer, then a melamine glue is applied, then a lower-grade lumber is layered
perpendicular to the rst, followed by another glue application and another layer of higher-
grade lumber. CLT panels can be constructed in this manner to produce panels of 3, 5, 7, or
in some cases 9 layers. Once the panel is assembled, it is pressed using pneumatic cylinders to
110 psi for approximately 30 minutes. Panels exit the press and are lifted by forklift to a CNC
machine. e nal step before shipping is that the CLT panels are sanded and wrapped for
protection during shipment.
e CLT production LCI input data was based on 2016 production from the Oregon
manufacturer. Data is based on a production of 3,398 m3 (3.05 × 7.32-m panels) of CLT per
year. At the time of data collection, the Oregon facility was still in a preliminary production
phase, so production and data based on the capacity of the facility was used for 2016. A weighed
average of three panel sizes represents the 3,398 m3/year and is shown in Table 2.
Cross-laminated timber is the main product in the manufacturing process, comprising
98.6% wood and 1.4% resin by mass (Table 3). ere is no waste wood product sent to a land-
ll or burned onsite for energy. ese ndings are consistent with recent wood product LCI
industry-wide surveys (Milota 2015). All wood waste generated by nger jointing, planning,
and the CNC machine are considered coproducts and leave the CLT system boundary with
some economic value to them. Based on the lumber input into the CLT facility, 83% ends up
in the CLT product, and 17% as coproducts. ese coproducts are used for energy o site or
feedstock for particleboard manufacturing.
Journal of Green Building 25
Transportation Inputs
e transportation of logs from the forest roadside after harvest is the rst transportation process
for CLT manufacturing (Table 4). Logs for the Oregon CLT manufacturer are delivered from
western Oregon to a softwood lumber production facility in Mill City, Oregon. As previously
noted, rough planed lumber is the feedstock input for CLT. It is transported by truck from the
sawmill facility to the CLT facility in southern Oregon, 169 miles away. e resin used in CLT
is transported both by road and by barge. e wrapping material used for the CLT comes from
the state of Washington by road.
TABLE 2. Panel sizes and allocation for a weighted-average CLT panel from Oregon
manufacturer.
CLT Pa nel
Allocation
of panels ft3/panel ft3/y r. m3/yr. # Panels/yr. Board f t/yr.
3-Layer 30% 82.5 36,000 1,019 436 741,701
5-Layer 60% 137.5 72,000 2,0391 524 1,483,402
7-L ayer 10% 192 .5 12,000 340 62 247,2 3 4
TOTA L 100% 120,000 3,398 1,022 2,472,336
ft3/bf = 0.049 (actual)
TABLE 3. Mass balance of CLT and coproducts produced at the Oregon CLT facility.
Primary product Unit A mount/m3Mass allocation
Inputs
Lumber inputs odkg 648.81 100%
Resin portion kg 7.45
Outputs
CLT m31
CLT odkg 544.68 82.8%
Wood portion odkg 53 7. 2 3
Planar shavings odkg 22.43 3.4%
Finger joint waste odkg 6.05 0.9%
Hundegger waste odkg 7.1 2 1.1%
CLT o spec and end cuts odkg 75.98 11.7%
odkg = oven dry mass in kilograms
26 Volume 14, Number 4
Resin Inputs
Oregon CLT is certied to use a non-urea melamine formaldehyde resin, not the melamine-
urea-formaldehyde resins more commonly used in structural laminated timber products in
North America (Table 4). e resin is used for both nger jointing and face bonding the lumber
in CLT production. e resin manufacturer for the Oregon CLT facility was AkzoNobel, which
produces a low-emission melamine 2-part clear resin. e resin is LEED Gold certied and
approved for interior and exterior use.
Energy Inputs
Energy and fuel requirements for the CLT production came from electricity, natural gas, and
diesel at the CLT facility (Table 4). Electricity was modeled using the Northwest Power Pool
Grid which includes coal, biomass, petroleum, geothermal, natural gas, nuclear, hydroelectric,
wind, and other energy sources (NWPP 2010). e source of fuel used to generate electric-
ity helps determine the type and amount of impact in the overall LCA. Non-renewable fossil
represents nearly 55% of the fuel source in the NWPP grid, whereas hydro, wind, solar, and
geothermal comprise about 41% of the electricity fuel sourcing. Oregon CLT production is
new, and several updates have been made to the manufacturing of CLT since data was collected,
e.g., installation of a CNC machine. e same facility produces cold-cure glulam, so it was
TABLE 4. Inputs for CLT production used to develop the life-cycle inventory.
Inputs Unit Amount Mode of Transport
Logs to sawmill mile (km) 67 (10 8) Road
Lumber to CLT mile (km) 169 (272) Road
Resin mile (km) 8,937 (14,373) Barge
Resin mile (km) 227 (365) Road
Hardener mile (km) 486 (782) Road
Wrapping material—Packaging CLT mile (km) 200 (322) Road
Lumber m31.21
Lumber odkg 648.81
Lumber delivery by truck tkm 176.4 6
MF resin kg 7.45
MF resin transport—ship tkm 107.10
MF resin transport—Truck tkm 2.72
Electricity kWh 98.90
Natural gas m34.18
Diesel L0.05
tkm = tonne-kilometer
Journal of Green Building 27
necessary to make assumptions about electricity, natural gas, and other fuels allocated to CLT.
e manufacturing facility allocated 30% of the total on-site electricity use to CLT production.
RESULTS AND DISCUSSION
Results are presented for three life cycle stages:
1. Cradle-to-gate for forestry operations (forest operations, harvesting),
2. Gate-to-gate for softwood lumber production (transport of logs, lumber sawing, drying,
and packaging), and
3. Gate-to-gate for CLT production using primary data.
Cradle-to-Gate LCIA Results
Environmental performance results for GWP, acidication, eutrophication, ozone depletion
and smog, calculated using the TRACI impact method are reported in Table 5. e cumula-
tive energy demand (CED) impact method results are also reported in Table 5 as total energy
and energy generated from non-renewables, renewables, wind, hydro, solar, and nuclear fuels.
Both mass allocation and economic allocation results are reported in Table 5. Transportation
is burdened to the receiving process, for example, log transport from the forest road is part
of the gate-to-gate of softwood lumber production. Resin production transport impacts are
part of the gate-to-gate CLT production. For our results, both lumber production and CLT
production would have a mass or economic allocation approach applied to them. For lumber
production, actual pricing for the lumber and coproducts was used, based on Milota (2015).
For the economic allocation of CLT, the value of the CLT product was greater than 10 times
the dierence in economic value across coproducts; therefore, the environmental burden of
CLT manufacturing is entirely allocated to CLT.
Recent studies have shown similar results in mass and economic approaches and highlight
the pros and cons of each of these allocation approaches (Taylor et al. 2017). In various wood
panel LCAs, an economic allocation of products and coproducts resulted in higher environmen-
tal impact for the main product. For Oregon CLT, the dierence in impacts was a 30% increase
in GWP from a mass allocation to an economic allocation, and 24% more energy when an
economic allocation was assigned (Table 5). Economic allocation likely will not be required in
the next round of PCR development. Consequently, our discussion of results is predominantly
based on mass allocation. e economic allocation is presented along with mass allocation in
order to highlight the dierences and provide relevant and necessary information to the readers.
Aside from the dierences between the two approaches, the production of 1 m3 of Oregon
CLT released 206 and 159 kg CO2 eq. for economic and mass allocation, respectively. CLT
production represented 57%–61% of the GWP impact, while lumber production and forestry
operations accounted for 28%–27% and 16%–12%, respectively. A similar impact allocation
was found in cradle-to-gate CLT production from Canada, where CLT represented 57% of
the impacts and lumber production and forestry accounted for 30% and 13%, respectively
(Structurlam 2013). While the allocation of impacts amongst life cycle stage are relatively similar
between the Canadian and Oregon CLT GWP results, the total GWP is not. e main reason
for these dierences is in the primary energy consumption between Canadian production opera-
tions and Oregon. Oregon forestry practices are more intensive, using more site-preparation
and harvesting methods (Oneil and Puettmann 2017). Oregon CLT is produced from a denser
wood species that requires more energy to transport, saw, and dry. In addition, the Canadian
28 Volume 14, Number 4
TABLE 5. Cradle-to-gate LCIA results for 1 m3 of CLT.
Impact category Unit To t a l
CLT
Manuf.
Lumber
Production
Forestry
Operations
Mass Allocation Approach
Global warming kg CO2 eq 158.67 97.06 42.71 18.91
Smog kg O3 eq 1.72 0.80 0.52 0.41
Acidication kg SO2 eq 0.09 0.04 0.02 0.02
Eutrophication kg N eq 30.90 9.66 10.61 10.63
Ozone depletion kg CFC-11 eq 1.75E-06 1.73E-06 9.29E-09 1.70E-08
Tota l e n e r g y MJ 4,716.34 1,523.01 3,016.66 176.67
Non-renewable, fossil MJ 2,298.80 1,499.48 622.78 176.54
Non-renewable, nuclear MJ 20.47 20.29 0.05 0.14
Renewable, biomass MJ 2,394.08 0.52 2,393.57 0.00
Renewable, wind, solar, geothermal MJ 0.70 0.70 0.00 0.00
Renewable, water MJ 2.29 2.02 0.27 0.00
Wood ber kg 585.30 0.00 0.00 585.30
Water L670.6 336.92 17. 2 9 670.60
Solid waste kg 18.23 3.46 0.18 18.23
Economic Allocation Approach
Global warming kg CO2 eq 206.26 116.75 5 7. 26 32.25
Smog kg O3 eq 41.98 11.57 12.27 18.14
Acidication kg SO2 eq 2.27 0.96 0.62 0.69
Eutrophication kg N eq 0.11 0.05 0.02 0.04
Ozone depletion kg CFC-11 eq 0.0 2.08E-06 8.43E-09 2.90E-08
Tota l e n e r g y MJ 5,839.96 1,832.03 3,706.50 301.43
Non-renewable, fossil MJ 2,954.8 1,803.69 8 4 7. 01 301.19
Non-renewable, nuclear MJ 24.71 24.45 0.03 0.23
Renewable, biomass MJ 2,859.65 0.62 2,859.03 0.00
Renewable, wind, solar, geothermal MJ 0.84 0.84 0.00 0.00
Renewable, water MJ 2.86 2.43 0.43 0.00
Wood ber kg 999.26 0.00 0.00 999.26
Water L828.68 381.20 4 17.9 9 29.50
Solid waste kg 22.54 17.57 4.65 0.31
Journal of Green Building 29
studies reported their results for lumber production using a mass allocation and the CLT using
an economic allocation (Milota and Puettmann 2017). If results for Oregon CLT were reported
in the same way, they would be lower too.
Energy calculations are from the CED impact assessment method (Table 5). Total energy
for producing 1 m3 of CLT was 4.7 GJ for mass allocation. Within the cradle-to-gate system
boundary, lumber production used the most energy, around 64% of the total cradle-to-gate;
CLT manufacturing consumed 32% of the total cradle-to-gate energy and forestry opera-
tions consumed 4%. Renewable biomass fuels represented the greatest proportion of energy
consumed (51%) for total cradle-to-gate energy use, all in the lumber production gate-to-gate
life-cycle stage. Non-renewable fossil fuels represented 49% of the total primary energy, with
the majority consumed in the CLT gate-to-gate life cycle stage (65%). Non-renewable nuclear
and renewable (solar/hydro/wind/etc.) represented less than 0.5% of the total primary energy.
ese fuels are used in the NWPP electricity grid.
Overall, the manufacturing of CLT in Oregon is around 50% energy self-sucient, when
considering the on-site use of renewable biomass for the lumber production process. e calcu-
lated GWP impact is limited to anthropogenic emissions of fossil carbon and does not include
biogenic CO2 emissions from the combustion of biomass. erefore, a higher energy demand
is reported with a low carbon impact.
ere is a total of 893 kg of wood ber consumed from cradle to gate to produce 1 m3 of
nished Oregon CLT. e wood ber begins as a log at the forest road. When it arrives at the
mill, approximately half will end up as nished rough lumber that may be used for CLT and
the rest will be co-products (chips, residues, and wood fuel). On average, wood fuel represents
about 22% of the co-product and is used for drying lumber (Milota and Puettmann 2017).
Total wood ber represents all the wood consumed from cradle to gate to produce 1 m3 of CLT,
including wood fuel, stickers, etc.
e non-renewable resources are inputs in fuel productions and electricity production
used at the lumber mill and CLT plant and for resin production and transportation processes.
Non-renewable resources are also inputs into the production of diesel, gasoline, natural gas,
oils, and lubricants.
Water consumed (50%) during lumber production was reported as used in the log yard,
where water is commonly sprayed on log decks to prevent staining and cracking of the logs. e
water associated to CLT gate-to-gate production is from the resin production. Very little solid
waste is generated from cradle to gate. Reported waste is packing material and “dirty” wood
waste generated in the log yard.
CLT Production Gate-to-Gate LCIA Results
e gate-to-gate results include operations directly associated with the onsite production of
CLT. Although economic results were higher than the mass allocation results, the relationship
between the input processes in the CLT gate to gate remained constant between mass and eco-
nomic allocations; this again emphasizes the impact that the lumber production process has on
cradle-to-gate LCA of CLT. Five life-cycle stages were considered in the CLT gate-to-gate LCIA
results: 1. energy consumed on site at the CLT facility; 2. transportation of the lumber to the
facility; 3. transportation of the resin to the facility; 4. production of packaging materials for the
CLT product; and 5. resin production. e percentage contribution of each life-cycle stage for
the six impact categories reported is presented in Figure 3. CLT production represents about half
30 Volume 14, Number 4
of the gate-to-gate impact for GWP and acidication and nearly half of the energy consump-
tion (47%). Onsite energy from Oregon CLT is primarily natural gas, which contributes to the
GWP value and the fossil-fuel use at the CLT facility (48%). e facility was built to expand
an existing cold-cure glulam process. e building itself is not well insulated; as a result, most
of the fuel consumption for CLT production comes from heating the building (Table 6). e
use of the MF resin accounts for 31% of the GWP and over half of the eutrophication impact
for its production. Lumber transport contributed over half of the smog impact, generating from
the trucking distance of 169 miles from the sawmill to the CLT facility.
Biogenic Carbon Accounting
It is known that tree growth, product production, fuel combustion, and decomposition or
combustion in landlls result in various uxes of CO2. Carbon is emitted to the atmosphere
as biomass CO2 or fossil CO2, depending on the fuel combusted. Carbon dioxide is also
sequestered, absorbed from the atmosphere by living trees during photosynthesis. is carbon
is part of the molecular structure of wood and remains in the wood of a wood product for the
product’s life. Cradle-to-gate carbon emissions to produce 1 m3 of CLT were, respectively, 159
and 206 kg CO2 eq for mass and economic allocations. at same 1 m3 of CLT stores 985 kg
CO2 eq based on the wood content only of the nished CLT panel (537 kg), and with a carbon
content of 50% (Table 7).
FIGURE 3. Gate-to-gate impact assessment results showing contribution by life-cycle stage (CLT
manufacturing, lumber production, and forestry operations)(mass allocation).
Journal of Green Building 31
TABLE 6. Allocation of gate-to-gate LCIA results for 1 m3 of finished CLT
Impact category
CLT Onsite
Energy
Tra nspor t
Lumber
Tra nspor t
resin
Pack aging
Material Resin
Mass Allocation Approach
Global warming 51% 14% 3% 0% 31%
Acidication 53% 24% 5% 1% 17%
Eutrophication 13% 26% 4% 1% 57%
Smog 29% 52% 10% 0% 10%
Ozone depletion 100% 0% 0% 0% 0%
Tota l e n e r g y 47% 14% 3% 1% 35%
Non-renewable, fossil 48% 14% 3% 1% 34%
Non-renewable, nuclear 0% 0% 0% 0% 100%
Renewable, biomass 0% 0% 0% 0% 100%
Renewable, wind, solar, geothermal 0% 0% 0% 0% 100%
Renewable, water 0% 0% 0% 0% 100%
TABLE 7. Net Cradle-to-gate carbon emissions.
Mass Allocation Economic Allocation
kg CO2 equivalent/m3
Forestry operations 19 32
Lumber production 43 57
CLT manufacturing 97 117
CO2 eq. stored in product –985 –985
Net cradle-to-gate carbon emissions 826 –778
CONCLUSIONS
e cradle-to-gate LCA for CLT is representative of CLT production and energy inputs for the
specic Oregon CLT manufacturing facility surveyed for the study. Both economic and mass
allocation approaches were reported. Under the economic allocation approach, 100% of the
CLT manufacturing impacts and upstream inputs were assigned to the CLT product. When
using the mass allocation approach, 83% of the onsite and upstream burdens were assigned
to the CLT product (cradle-to-gate). For lumber inputs, the mass allocation approach yielded
32 Volume 14, Number 4
lower impact values. In our LCA assessment of CLT, this was signicant when lumber produc-
tion allocations were changed from 50% to 86% for mass and economic allocation approaches,
respectively. e impact this had on the cradle-to-gate LCA of CLT product is that under a mass
allocation approach, 50% of the upstream burdens are transferred to CLT, while an economic
approach increases that burden to 83%.
e CLT manufacturing stage drives most of the environmental impacts from cradle to
gate. is is primarily due to resin production for CLT and the onsite energy consumption,
primarily natural gas. Softwood lumber production consumed most of the energy used for
drying the lumber. Life-cycle impact categories are mostly driven by the type of fuel used and
whether the fuel is non-renewable or renewable. Lumber production (gate-to-gate) used nearly
100% of the heat energy, with self-generated biomass fuels for kiln operation, while fossil fuels
remained the main energy source during CLT production. Wood waste was generated during
CLT manufacturing (~17% of input material) and was used for energy at on osite lumber mill
(not associated with CLT manufacturing), or it was sold to a particleboard manufacturing facil-
ity osite and used as a wood feedstock. No wood waste was burned on site or sent to a landll.
In this study, CLT manufacturing contributed the greatest amount to the global warming
impact category, while the softwood lumber production stage consumed the most energy.
Natural gas use was the main contributor to the GWP value for CLT, while biomass represented
75% of the energy for lumber production (cradle-to-gate). Reducing the amount of natural
gas used at the CLT manufacturing would lower the cradle-to-gate carbon footprint. Carbon
was released as CO2 during all life-cycle stages. Cross-laminated timber stores 985 kg CO2 eq.
and releases from cradle-to-gate 206 and 159 kg CO2 eq for economic and mass allocation,
respectively. e production of Oregon CLT from cradle-to-gate has a negative carbon emis-
sion of 784 kg CO2 eq. Oregon CLT stores more carbon in the nal product than is emitted
during cradle-to-gate production.
Resin production also has a signicant contribution to the GWP and the eutrophication
impact categories for use in CLT. In these two impact categories, resin contributed 31% and
57% to GWP and eutrophication, respectively.
ACKNOWLEDGMENTS
e authors would like to thank the USDA National Institute of Food and Agriculture’s
UW-SEFS McIntire-Stennis grant, project no. WNZ-04162015-GE—Accession No. 1006435,
for funding this this work.
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Life cycle assessment (LCA) has been widely used to determine the environmental impact of mass timber construction (MTC) as a substitute for conventional construction. This article presents a systematic review of MTC from a life cycle assessment perspective. The goal and scope definition, life cycle inventory analysis, impact assessment and interpretation are examined and analyzed in 62 peer-reviewed articles. The results show the variety in scope, lifespan, system boundary, data sources and indicators. Studies on MTC have been conducted at the building material, component, structure, and entire building levels, as well as at the urban level. The majority of studies compare the LCA of reinforced concrete (RC) and cross laminated timber (CLT) buildings. The global warming potential (GWP) and life cycle energy are the most frequently evaluated category indicators among the articles. It is found that the average embodied energy of mass timber buildings is 23.00% higher than that of RC alternatives, while the average embodied greenhouse gas (GHG) emissions of RC buildings are 42.68% higher than that of mass timber alternatives. There is a clear general trend that mass timber buildings generally have lower GWP and life cycle primary energy (LCPE) than RC and steel buildings. Eventually, sensitivity analysis, carbon storage and outlook of the mass timber are also reviewed and discussed in the literature.
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Purpose This paper reviews the state-of-the art research in life cycle assessment (LCA) applied to buildings. It focuses on current research trends, and elaborates on gaps and directions for future research. Methods A systematic literature review was conducted to identify current research and applications of LCA in buildings. The proposed review methodology includes (i) identifying recent authoritative research publications using established search engines, (ii) screening and retaining relevant publications, and (iii) extracting relevant LCA applications for buildings and analyzing their underpinning research. Subsequently, several research gaps and limitations were identified, which have informed our proposed future research directions. Results and discussions This paper argues that humans can attenuate and positively control the impact of their buildings on the environment, and as such mitigate the effects of climate change. This can be achieved by a new generation of LCA methods and tools that are model based and continuously learn from real-time data, while informing effective operation and management strategies of buildings and districts. Therefore, the consideration of the time dimension in product system modeling is becoming essential to understand the resulting pollutant emissions and resource consumption. This time dimension is currently missing in life cycle inventory databases. A further combination of life cycle impact assessment (LCIA) models using time-dependent characterization factors can lead to more comprehensive and reliable LCA results. Conclusions and recommendations This paper promotes the concept of semantic-based dynamic (real-time) LCA, which addresses temporal and spatial variations in the local built and environmental ecosystem, and thus more effectively promotes a “cradle-to-grave-to-reincarnation” environmental sustainability capability. Furthermore, it is critical to leverage digital building resources (e.g., connected objects, semantic models, and artificial intelligence) to deliver accurate and reliable environmental assessments.
Conference Paper
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The Cross-Laminated Timber (CLT) has been receiving special attention in recent research as an alternative for climate change mitigation since it is a renewable source and can remove and stock high amounts of CO2 from the atmosphere. Some countries, such as Brazil, still do not have mature and large CLT industry. However, the development of this industry in other countries is expected since the CLT is considered the main wood material to be used in high-rise mass timber buildings. It is particularly important to have environmental information, especially concerning the climate change impacts, in terms of life cycle greenhouse gas (GHG) emissions, for this product to increase its competitiveness in a new market. In this context, this research aimed to evaluate three different Life cycle inventories (LCIs) for CLT production of studies from Japan and the United States. Based on the first findings, we summarized the critical items in the LCI of CLT production and listed some actions for the reduction of GHG emissions that occur in this process. The LCIs are adapted considering the context of Brazil (a country with a cleaner electricity matrix) and China (a country with the highest share of fossil fuels). The main inconsistencies present in the LCIs are presented and discussed. The GHG emissions are concentrated in the following hotspots: (1) Roundwood production; (2) electricity consumption; and (3) adhesives production for CLT production. Therefore, the reduction of the consumption of these materials and activities should be encouraged for the decrease of GHG emissions. The data of Roundwood used in the modelling severely affects the final results. Their GHG emissions are related to the consumption of diesel in forestry activities. This research brings insights into the evaluation of the life cycle GHG emissions from the production of CLT.
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This study was an update on the 2000 LCI data on material and energy inputs associated with the production of one cubic meter (m3) of glued-laminated timbers (glulam) produced in the Pacific Northwest (PNW) and the Southeast (SE) regions of the United States. This study looks at the cradle to gate for the entire glulam production processes which include forest harvest, lamstock production, and glulam beam production. Data collected from glulam beam manufacturers in 2013 allowed for the development of a life cycle assessment (LCA) utilizing the product category rules (PCR) for North American Structural and Architectural Wood Products, so that the results from these analyses can be used for the development of environmental product declarations (EPDs) of glulam beams produced in the US. Comparing the results of this study to the LCA based on the 2000 survey data, it shows 29% reductions in global warming potential (GWP) of glulam beams produced in both the PNW and SE and reductions in the use of energy derived from fossil fuels by 39% in the PNW and SE. The overall net carbon sequestered in one m3 of PNW glulam is equivalent to 938 kg of CO2 and 1,038 kg of CO2 in the SE. Utilizing techniques that reduced the use of electricity and minimizing the transportation distances of the raw materials and resins to the mill could help to further reduce the carbon footprint of the glulam beam manufacturing process.
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Wood processing often involves an array of products and co-products and a cascade of primary and secondary uses. Prior life cycle assessment (LCA) reporting allocated environmental burdens to products and co-products based on mass for multi-product systems to develop environmental product declarations. Environmental product declarations are developed from LCAs following the procedures detailed in product category rules (PCRs). A recent PCR for North American Structural and Architectural Wood Products requires allocation by economic value when the main products exceed the value of coproducts by greater than 10 percent. Using recent LCAs of wood-based panels, this paper describes the differences in LCA results when using mass and economic allocation methods. For wood panel products that do not use wood residues from primary wood manufacturers (e.g. plywood), an increase in environmental impacts results from an economic allocation approach. For wood panel products made from wood residues (e.g. cellulosic fiberboard), there is a slight decrease in most environmental impact metrics with economic allocation. Sensitivity and variability in LCA results are discussed for the mass and economic allocation approaches.
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Transparency of environmental impacts for building products are of increasing concern. For wood building products, updating life cycle assessment (LCA) data are critical to ensure the corresponding environmental product declarations are of the proper recency to maintain this transparency. This study focused on the developing up-to-dated life cycle inventory (LCI) and associated life cycle impact assessment (LCIA) data for composite I-joist production in Southeast (SE) and Pacific Northwest (PNW) regions of the United States. Components of the I-joist production system included in the analysis were laminated veneer lumber (LVL), finger-jointed lumber (FJL), and oriented strand board (OSB) while this study considered five life cycle stages including forestry operations and I-joist manufacturing in addition to the production of the components. Primary 2012 production data were collected and analyzed and the resultant LCI flow and LCIA were modeled on a declared unit of 1.0 km. The cradle-to-gate pri...
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To keep environmental product declarations current, the underlying life-cycle inventory (LCI) data and subsequent life-cycle assessment (LCA) data for structural wood products must be updated. Using weight-averaged production primary data collected from industry for the year 2012, LCIs were updated for laminated veneer lumber (LVL) production on a 1.0 m3 basis in the Southeast (SE) and Pacific Northwest (PNW) regions of the United States. In addition, a cradle-to-gate life-cycle impact assessments (LCIAs) were performed to assess the environmental impacts associated with LVL production for both regions. The cradle-to-gate LCIAs included three life cycle stages: forestry operations, dry veneer production, and LVL production. The LCIs revealed that the dry veneer life-cycle stage dominated overall primary energy consumption for both the SE and PNW at 6.83 (68.5%) and 6.75 GJ/m3 (75.3%), respectively. Energy consumption at veneer stage was primarily based on renewable sources, especially wood fuel c...
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The objective of this project was to quantify and compare the environmental impacts associated with alternative designs for a typical North American mid-rise office building. Two scenarios were considered; a traditional cast-in-place, reinforced concrete frame and a laminated timber hybrid design, which utilized engineered wood products (cross-laminated timber (CLT) and glulam). The boundary of the quantitative analysis was cradle-to-construction site gate and encompassed the structural support system and the building enclosure. Floor plans, elevations, material quantities, and structural loads associated with a five-storey concrete-framed building design were obtained from issued-for-construction drawings. A functionally equivalent, laminated timber hybrid design was conceived, based on Canadian Building Code requirements. Design values for locally produced CLT panels were established from in-house material testing. Primary data collected from a pilot-scale manufacturing facility was used to develop the life cycle inventory for CLT, whereas secondary sources were referenced for other construction materials. The TRACI characterization methodology was employed to translate inventory flows into impact indicators. The results indicated that the laminated timber building design offered a lower environmental impact in 10 of 11 assessment categories. The cradle-to-gate process energy was found to be nearly identical in both design scenarios (3.5 GJ/m2), whereas the cumulative embodied energy (feedstock plus process) of construction materials was estimated to be 8.2 and 4.6 GJ/m2 for the timber and concrete designs, respectively; which indicated an increased availability of readily accessible potential energy stored within the building materials of the timber alternative.
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Life-cycle inventory (LCI) and life-cycle assessment (LCA) were used to provide quantitative assessments of the environmental impacts of forest management activities that are required to produce feedstock for wood products such as lumber, engineered panels, and pulp. Primary and secondary data were gathered for the Pacific Northwest Douglas-fir region of the United States to produce an attributional LCA that includes planting, growing, and harvesting trees that are destined for use in wood manufacturing. Using the Tool for the Reduction and Assessment of Chemical and other environmental Impacts (TRACI) method, under average management conditions, forest operations can expect to generate from 10 to 18 kg CO2 equivalent (CO2 eq) per cubic meter (m³) of logs ready to leave the landing for the manufacturing facility, depending on the amount of forest residues that are piled and burned. This same cubic meter of log plus bark will have sequestered 960 kg CO2 eq during its growth cycle, for a net greenhouse gas sink of 942 to 950 kg CO2 eq per m³. Forest management impacts are from 1 to 13 percent of the total impacts from the cradle to gate for global warming potential and the potential to increase smog, eutrophication, and acidification. Upstream impacts associated with the production of herbicides are reflected in the ozone potential impact category. These LCA results can be used as upstream processes for wood manufacturers interested in developing Environmental Product Declarations for products that use these resources as inputs.
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Wood is the predominant construction material in the US residential sector. In commercial and midrise construction, the use of wood is limited compared with reinforced concrete and steel. Wood, being a natural, renewable material that sequesters carbon, is a natural fit for newer construction with enhanced sustainability goals. The objective of this study is to evaluate and identify the environmental utility (avoided emissions) of using wood in place of steel and concretc in the commercial construction and renovation sectors in Oregon, United States. The study used comparative, cradle-to-grave, life-cycle analysis, with Athena Impact Estimator for Buildings. Six case studies that represent different building functionalities, material systems, and construction techniques were modeled via the user interface input option, and the results were evaluated for global warming potential (GWP) and impacts on energy sources, such as fossil fuel consumption, when structural materials arc substituted using wood. Out of the six case studies, one building was completely redesigned as per current codes using wood as the major structural material. Bills of materials for both wood redesigns and the as-built designs were used as input in the software and subsequently analyzed. Results showed that the average reduction in GWP due to wood substitution was about 60% across the six case studies. These findings reinforce the perception of wood as a green building material having potential for commcrcial construction.
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A cradle-to-gate life cycle inventory was done for 2x4 to 2x12 dimension lumber produced from logs in the Pacific Northwest (PNW) and Southeast (SE) regions of the United States based on 2012 lumber and co-product production, raw material and fuel use, electricity consumption, and on-site emissions. The mills represented 17% and 11% of the production volumes in the regions, respectively. Five processes existed within the mill, logyard, sawing, drying, planing, and energy generation. Data for the first four processes came exclusively from the survey. The functional unit was 1 m3 of planed dry wood. Data for energy generation was based on nationwide wood boiler survey that included the Pacific Northwest lumber mills. The cradle-to-gate processing energy in the PNW region was 3,434 MJ per m3 of planed, dry lumber, 96% of which is due to log transport and wood processing. The value was higher, 5151 MJ/m3, for the SE region in part due to a higher initial wood moisture content. In each region over 70%...
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This paper presents the Life-Cycle Assessment (LCA) of alternative building materials from forest resource regeneration or mineral extraction through product manufacturing, the assembly of products in constructing a residential home, occupancy and home repairs, and the eventual disposal or recycle. A unique feature of this study's LCA framework is that temporal distribution of events and associated environmental effects during the seed to demolition life cycle were considered by extending the scope to include forest growth through to demolition of the builidng. Our approach was to first conduct LCIs that quantified the energy, resource use, and emissions associated with a particular product, service, or activity. We followed this activity with the assessment of the house, and investigated the potential environmental consequences of energy and resource consumption and waste emissions. Finally we identified improvement opportunities for future research.