ArticlePDF Available

Comparative life-cycle assessment of a mass timber building and concrete alternative

Shaobo Liang
Postdoctoral Research Fellow
Hongmei Gu*
Research Forest Products Technologist
Richard Bergman
Project Leader and Research Wood Scientist
USDA Forest Products Laboratory
Madison, WI 53726
Stephen S. Kelley
Department of Biomaterials
North Carolina State University
Raleigh, NC 27695
(Received January 2020)
Abstract. The US housing construction market consumes vast amounts of resources, with most structural el-
ements derived from wood, a renewable and sustainable resource. The same cannot be said for all nonresidential
or high-rise buildings, which are primarily made of concrete and steel. As part of continuous environmental im-
provement processes, building life-cycle assessment (LCA) is a useful tool to compare the environmental footprint of
building structures. This study is a comparative LCA of an 8360-m
, 12-story mixed-use apartment/ofce building
designed for Portland, OR, and constructed from mainly mass timber. The designed mass timber building had a
relatively lightweight structural frame that used 1782 m
of cross-laminated timber (CLT) and 557 m
of glue-
laminated timber (glulam) and associated materials, which replaced approximately 58% of concrete and 72% of rebar
that would have been used in a conventional building. Compared with a similar concrete building, the mass timber
building had 18%, 1%, and 47% reduction in the impact categories of global warming, ozone depletion, and
eutrophication, respectively, for the A1-A5 building LCA. The use of CLT and glulam materials substantially
decreased the carbon footprint of the building, although it consumed more primary energy compared with a similar
concrete building. The impacts for the mass timber building were affected by large amounts of gypsum board, which
accounted for 16% of total building mass. Both lowering the amount of gypsum and keeping the mass timber
production close to the construction site could lower the overall environmental footprint of the mass timber building.
Keywords: Cross-laminated timber, environmental assessment, life-cycle analysis, tall wood building.
The building industry is a heavy user of resources
and is responsible for more than 30% of total global
energy consumption and for about 40% of global
* Corresponding author
SWST member
This article was written and prepared by US Government
employees on ofcial time, and it is therefore in the public
domain and not subject to copyright.
Wood and Fiber Science, 52(2), 2020, pp. 217-229
© 2020 by the Society of Wood Science and Technology
carbon dioxide emissions (Jones et al 2016; Berardi
2017). Developing energy-efcient and low-impact
buildings has become increasingly important. The
use of wood as a building material can provide
substantial economic and environmental benets
(Ritter et al 2011). Mass timber products, including
cross-laminated timber (CLT), glue-laminated tim-
ber (glulam), and nail-laminated timber, have been
demonstrated to be green building materials with a
lower carbon footprint than their concrete and steel
alternatives (Perez-Garcia et al 2005; Karacabeyli
and Douglas 2013; Bowers at al. 2017; Gu and
Bergman 2018). Also, CLT and other mass timber
products offer additional advantages such as faster
erection times, easier material handling, a high level
of prefabrication at the material manufacturing site,
and less waste generation and noise pollution during
the construction stage (Kremer and Symmons 2015;
Connolly et al 2018; Smith et al 2018). In particular,
the construction phase of a mass timber building can
result in substantial savings with quicker erection
times, more than 50% faster than other alternative
materials (APA 2019).
CLT is a massive structural composite panel fab-
ricated with kiln-dried dimensional lumber stacked
in three to nine layers arranged perpendicular to
each other (APA 2012). The production of similar
perpendicular engineered wood products dates back
to the early 20th century in the United States
(Walch and Watts 1923). The use of CLT in mid- to
high-rise buildings began to appear several decades
ago in European countries (FII 2016; Espinoza
and Buehlmann 2018). More recently, CLT and
other mass timber technologies have captured the
interest of designers, developers, property owners,
industry, and governments in North America
(Podesto and Berneman 2016; Williamson and
Ross 2016). The revised 2021 International
Building Code includes provisions for new con-
struction Type IV-A/B/C for up to 18 stories for
business and residential buildings using mass
timber (Breneman and Richardson 2019). Using
mass timber in building systems could be a boost to
the wood industry sector, but to gain the support of
green building advocates, rigorous scienticanal-
ysis on the environmental impacts is required. The
whole-building life-cycle assessment (LCA) is a
method to analyze building environmental impacts
based on ASTM E2921 (ASTM 2016) and EN
15978 (EN 2011) standards. However, only few
LCA studies on CLT and other mass timber
buildings are publicly available (Cadorel and
Crawford 2018). These studies all agree that mass
timber buildings have better environmental perfor-
mance such as lower greenhouse gas (GHG)
emissions compared with alternative concrete
buildings, although different study periods or sys-
tem boundaries were applied (Robertson et al 2012;
Durlinger et al 2013; Grann 2013; Bowick 2015,
2018). LCA case studies for mass timber buildings
in the United States are very limited (Gu and
Bergman 2018; Pierobon et al 2019) because few
buildings have gone beyond the concept stage.
More importantly, there are very few studies that
directly compare the LCA implications for mass
timber and concrete steel buildings, with similar
size, function, and operational energy perfor-
mance. It is critical to conduct more studies to
assess the environmental impacts of mass timber
buildings and to further analyze the impacts on
local communities, forest health, and the regional
This study conducted a building LCA for a 12-story
mixed-use tall wood building in Portland, OR, that
comprises CLT and glulam as the main structural
building materials. The LCA of this mass timber
building was compared with a functionally equiva-
lent concrete building system, with no wood struc-
tural elements. The environmental impacts of the two
buildings were categorized using the Tool for the
Reduction and Assessment of Chemical and other
environmental Impacts (TRACI) 2.1 impact method
(Bare et al 2012), and a detailed contribution analysis
and carbon accounting metrics were performed. This
research is part of a more comprehensive project
investigating the CLT supply chain along with po-
tential economic contributions and environmental
implications of increased CLT and other mass timber
building construction (Kelley and Bergman 2017).
Results generated from this study will provide solid,
transparent evidence on the environmental perfor-
mance metrics for CLT and other mass timber
buildings that can inform the public, building de-
velopers and owners, and policy makers.
Goal and Scope
The goal of this study was to quantify the environ-
mental impacts of a tall wood building built primarily
with CLT and glulam structural elements and compare
those impacts with a functionally equivalent building
with traditional concrete materials. The target building
for this cradle-to-site LCA study is an 8360-m
, 12-
story, mixed-use ofce and apartment complex. The
building was designed to be built in Portland, OR, and
to have the same re-proong performance, insulation,
and energy consumption outcomes as a functionally
equivalent concrete building design. Both building
designs were completed by LEVER Architecture
(Portland, OR) with additional structural design and
analysis from their partner, KPFF Engineering
(Seattle, WA). Both buildings comply with Type 1B
re-resistant construction code with noncombustible
capacities of 2-h exterior walls, 2-h structural frame,
2-h ceiling/oor separation, and 1-h ceiling/roof
assembly (Heppner 2019). The building structure
components to compare include ceilingroof,
oors, foundation, postbeams, and walls.
Functional Unit and System Boundary
The functional unit for this study is dened as 1 m
oor area of the whole building. The system
boundary of this building LCA is dened as cradle-
to-site, as illustrated in Fig 1, and includes the
modules A1-A3 Product Stage and modules A4 and
A5 Construction Process Stage. More specically, in
this study, module A1 Raw materials supply covers
raw material acquisition (eg from tree seeding to log
harvest, or cement and aggregate mining and pro-
duction); module A2 Transport covers the trans-
portation of raw materials to the manufacture plant
(eg truck loading logs and transporting to primary and
secondary wood products manufacturers, or trans-
portation of cement and aggregate and rebar); module
A3 Manufacturing covers the gate-to-gate production
of secondary products (eg mass timber products
processing and packaging at the plant, or formulated
concrete); module A4 Transport covers the trans-
portation of materials and products from the factory
gate to the building site (eg trucking all construction
materials to the building site), whereas the trans-
portation of construction equipment to and from the
site was excluded; and module A5 Construction
installation process only covers the energy
consumption to install building materials into the
building (eg diesel usage by crane to lift CLT and
pour/pump concrete), whereas ground works,
labor assembly, land use, and other things were
Figure 1. Cradle-to-site life-cycle assessment system boundary for the mass timber and concrete buildings.
Life-Cycle Inventory (LCI) and Impact
The LCI phase in this study measures the materials
use (modules A1-A3), transportation (module A4),
and direct energy (module A5) inputs for the
construction process of the proposed CLT and
concrete buildings. Table 1 summarizes the
quantities of building materials used for the two
buildings, which were designed with the same
U-value. These quantities were provided by the
building designer (LEVER Architecture). The
building materials transport distances to the
Table 1. Quantities of materials and life-cycle inventory data sources for mass timber and concrete buildings.
Building section/material Unit Mass timber building Concrete building Database/source
Ceiling and roof
Hollow structural steel kg 11,449 7415 AIE
0.95 Chen et al 2019
1-inch mineral wool m
285 285 DataSmart
Acrylic latex paint L 3096 1548 DataSmart
1-inch polystyrene board m
144 144 DataSmart
Steel sheet kg 5693 5693 DataSmart
5/8-inch gypsum board, re-resistant m
14,907 5945 AIE
1/2-inch gypsum board, regular m
4154 3337 AIE
Acrylic adhesive L 117 117
1279 Chen et al 2019
Coated steel deck kg 110 110 AIE
Hollow structural steel kg 400 400 AIE
Concrete m
932 1878 DataSmart
Mortar kg 4737 4737 DataSmart
3/8-inch plywood m
661 661 DataSmart/USLCI
1-inch polystyrene board m
4067 4067 DataSmart
Rebar kg 53,177 170,348 DataSmart
Steel sheet kg 4193 875 DataSmart
Steel welded wire mesh kg 110 110 AIE
60-mil TPO membrane m
351 351 AIE
Concrete m
125 149 DataSmart
Rebar kg 38,590 57,884 DataSmart
Post and beam
Hollow structural steel kg 43,527 39,230 AIE
Composite wood I-joist kg 60 60 DataSmart/USLCI
Concrete m
162 DataSmart
Glulam m
557 DataSmart/USLCI
Rebar kg 22,089 DataSmart
Steel sheet kg 830 823 DataSmart
Aluminum extrusion kg 31,039 31,051 DataSmart
502 Chen et al 2019
Hollow structural steel kg 31,947 30,026 AIE
Concrete m
48 438 DataSmart
Concrete masonry unit kg 71,031 70,908 DataSmart
3/8-inch plywood m
3230 3230 DataSmart/USLCI
Mortar kg 90,113 89,824 DataSmart
Acrylic latex paint L 9100 5143 DataSmart
1-inch polystyrene board m
7643 7644 DataSmart
Silicone sealant L 503 503 DataSmart
Rebar kg 12,078 125,951 DataSmart
5/8-inch gypsum board, re-resistant m
57,330 47,097 AIE
construction site were provided by LEVER Ar-
chitecture (Heppner 2019). It is noteworthy that
concrete used a transportation distance of 24 km,
and the CLT and glulam were sourced with a
transportation distance of 320 km. Direct energy
inputs for the construction installation were
estimated as diesel usage using an empirical
equation provided by Athena Sustainable Ma-
terials Institute (Finlayson 2019). The LCI of the
CLT production process model was provided by
the University of Washington (Chen et al 2019).
Other building materials, transportation, and
energy LCI data were sourced from the USLCI
and US Ecoinvent 2.2 (DATASMART 2019)
and Athena Impact Estimator (AIE) databases
and from the Pacic Northwest forest resources,
as listed in Table 1.
The life-cycle impact assessment (LCIA) inte-
grates the LCI data of each building stage
(modules A1-A5) to quantify the total life-cycle
environmental impacts, following the ISO 14040
(ISO 2006a) and ISO 14044 (ISO 2006b) envi-
ronmental management standards. The total en-
vironmental impacts were modeled using data
sources in SimaPro 8.5 software (PR´
e Sustain-
ability, Amersfoort, the Netherlands) and AIE for
Building 5.6 software (Athena Sustainable Ma-
terials Institute, Ottawa, Canada), and the TRACI
2.1 impact method (Bare et al 2012) was used in
SimaPro and AIE. The primary energy consump-
tion, categorized as nonrenewable (fossil and nu-
clear) and renewable (biomass, solar, wind, and
hydropower), was calculated using the embedded
cumulative energy demand (CED) method v1.10 in
SimaPro and AIE. The impact indicators calculated
for each building material from the two software
were extracted into Microsoft Excel spreadsheets
and then integrated for further analysis.
Sensitivity Analysis
Although the United States has signicant lumber
manufacturing capacity, there is limited CLT
manufacturing capacity. However, with increasing
interest in this emerging product, new capacity is
developing across the United States. Thus, CLT
transportation distances to the construction site
were varied in determining the portion of this
specic variable on the whole-building environ-
mental impact. The current distance was 320 km,
which assumes transport from a nearby local fa-
cility. Sensitivity analyses included middle dis-
tance by truck (768 km) from Inland Northwest
(INW), long distance by truck (465 km) and rail
(4189 km) from eastern United States; and oversea
distance by sea (21,333 km) from Europe, rail
(1103 km), and truck (335 km).
Comparison of Building Materials
The quantities of building materials of each
building section (ceilings-roof, oor, foundation,
postbeam, and wall) for the mass timber and
concrete buildings are shown in Table 1. Gen-
erally, the mass timber building uses a total of
2376 m
of wood products with 98% CLT and
glulam. In this study, mass timber usage is about
0.28 m
per m
of oor area. Other CLT and mass
timber building designs have used between 0.1
and 0.45 m
per m
of oor area (Gustavsson et al
2010; Oregon BEST 2017; Gu and Bergman
2018). Specically, the walls use 502 m
of 7-
and 9-ply CLT, the oors use 1279 m
of 5-ply
CLT, and the postbeams use 557 m
of glulam for
columns and beams. In addition, the mass timber
building also uses a signicant amount of con-
crete and steel, eg 1104 m
concrete and
103,845 kg rebar. The concrete and steel are used
on the foundation and also to stiffen the CLT oor
elements. The concrete building uses no mass
timber but uses 2627 m
of concrete and 376,272 kg
of rebar. In addition, to comply with Type 1B re-
resistant construction code, approximately 36%
more gypsum board is applied to the mass timber
building than the concrete building.
As shown in Fig 2, the total mass of the mass
timber building is about 68% of the functionally
equivalent concrete building. It is important to
keep in mind that the density of concrete
(2400 kg/m
) is much higher than the density of
the two mass timber products and wood building
products in general (550 kg/m
). The total mass
of the concrete building is 7.5 million kg for all
ve structural sections, whereas the total mass of
the mass timber building is only 5.1 million kg. In
the mass timber building, except for the ceilings-
roof which uses more gypsum board and attached
materials for re resistance purposes, the mass of
other building sections is about 64%, 81%, 76%,
and 66% of the concrete building for oors,
foundation, postbeams, and walls, respectively.
Light-weight mass timber buildings tend to have
lower carbon footprints and lower costs than
heavier concrete buildings (Connolly et al 2018).
Environmental Impact Analysis
The comparative cradle-to-site whole-building
LCIA results for 1-m
oor area of the mass
timber and concrete buildings are shown in
Table 2. Global warming contribution of the mass
timber building was found to be 18% lower
(193 kg CO
) than that of the concrete
building (237 kg CO
). The mass timber
building performs better in eutrophication than
the concrete building (47% lower), whereas the
concrete building has better performance in the
impact categories of smog and acidication (3%
and 16% lower than the mass timber building,
respectively). In addition, the two buildings are
essentially the same for ozone depletion (1%
difference), which is dominated by the use of
polystyrene insulation boards (XPS). The two
buildings used about the same amount of XPS.
Primary energy consumption, also called CED,
which describes the direct and indirect energy use
throughout the life cycle of products, is an
Figure 2. Total mass for the mass timber and concrete buildings.
Table 2. Life-cycle impact assessment results for 1-m
oor area by building types.
Impact category Unit Mass timber building Concrete building Percentage difference (%)
Global warming kg CO
eq 193 237 18
Ozone depletion kg CFC-11 eq 1.91E-04 1.93E-04 1
Smog kg O
eq 15.74 15.22 3
Acidication kg SO
eq 1.03 0.89 16
Eutrophication kg N eq 0.19 0.36 47
Total primary energy MJ 2868 2673 7
Nonrenewable, fossil MJ 2344 2371 1
Nonrenewable, nuclear MJ 198 242 18
Renewable MJ 326 61 439
important driver of environmental impacts and is
indicative for many environmental problems
(Huijbregts et al 2006). As shown in Table 2, the
mass timber building has 7% higher CED than the
concrete building, which is mainly caused by the
relatively higher unit CED of 2629 MJ/m
CLT than 1540 MJ/m
for concrete. In the mass
timber building, the large mass of CLT results in
CLT having the highest CED (23% of building
CED), followed by 22% for glulam. In the al-
ternative concrete building, rebar has the greatest
CED, accounting for 47% of building CED,
followed by 21% for concrete. In addition, fossil
fuel accounts for 82-90% of building CED for
both buildings, and renewable energy accounts
for 12% and 2% of building CED for the mass
timber and concrete buildings, respectively. As
expected, the mass timber building also uses
substantially higher renewable energy than its
concrete alternative building. This was mainly
because of the wood products manufacturer using
mill residue as an alternative heating source to dry
the lumber before CLT and glulam production
(Bowers et al 2017; Chen et al 2019).
The normalized environmental impacts and en-
ergy demand for the mass timber and concrete
buildings at different life-cycle phases are illus-
trated in Fig 3. The product phase (modules A1-
A3) is the dominant contributor, accounting for
88-98% in all impact categories for the two
buildings. The transport phase (module A4)
contributes 3-8% to the impact categories of
global warming, smog, acidication, eutrophi-
cation, total primary energy, and fossil fuel
consumption for the mass timber building. Be-
cause of the longer transportation distance of
wood building materials from the manufacturer to
construction site, eg 320 vs 24 km for materials
for the concrete building, the transportation im-
pacts are greater in the mass timber case than in
the all-concrete case.
The construction installation phase (module A5)
contributes a small fraction (1-5%) in all impact
categories except for ozone depletion, although
the impacts are consistently lower for the less
dense mass timber materials than for concrete.
The assessment for this phase, module A5, is based
on the estimation of diesel consumption used for
lifting all the building materials (Finlayson 2019).
When more empirical data on diesel consumption
by construction equipment and time for mass
timber building construction are collected, more
precise LCIA results can be reported for this phase.
Figure 4 compares the product phase (modules
A1-A3) environmental impacts from each
building section for the mass timber and concrete
buildings. Floor is the largest contributor for both
Figure 3. Normalized impacts for mass timber (left column) and concrete (right column) buildings at different life-cycle
buildings and accounts for 40-50% in the impact
categories of global warming, smog, and eutro-
phication, followed by the wall sections at 31-
39%. Specically, the building materials of CLT
and concrete/rebar in the mass timber building, as
well as concrete/rebar in the concrete building,
dominate the impacts of the oor component (93-
99%). For acidication, wall is the largest con-
tributor, accounting for 39-48% of impacts for the
two buildings. This is caused by the use of
gypsum board. Wall and oor together contribute
98-99% of the ozone depletion for both buildings,
which is because of the insulation material, eg
polystyrene boards (XPS). Although XPS ac-
counts for only 0.4% of the total mass quantities
in wall components in the mass timber building, it
contributed more than 99% of total ozone de-
pletion impacts. We strongly suggest that an
alternative product be considered. The ceilings-
roof, foundation, and postbeams together con-
tribute less than 27% to all impact categories for
the two buildings, although the mass timber
building contributes a higher fraction than the
concrete building in these building sections.
These differences are caused by the greater use of
gypsum board in the ceilings-roof, rebar in the
foundation, and glulam in the postbeams.
MasterFormat is a standard for organizing
specications and other written information for
commercial and institutional building projects in
the United States and Canada. It provides a
structured hierarchy for building construction
requirements and associated activities (Tecchio
et al 2018). To further analyze the environmental
impact contribution, the building materialsLCIs
were grouped into individual construction divi-
sions based on MasterFormat (CSI 2016), eg
Division 03: Concrete;Division 04: Masonry;
Division 05: Metals;Division 06: Wood, Plastics,
Composites;Division 07: Thermal and Moisture
Protection; and Division 09: Finishes. Figure 5
shows the comparison in the product phase
(modules A1-A3) of the environmental impacts
from individual construction divisions for the
mass timber and concrete buildings. The two
buildings have signicant differences in all im-
pact categories except for ozone depletion, which
was dominated by Division 07 for both buildings,
eg XPS. Because the insulation packages are
essentially the same, materials such as XPS,
aluminum panels, mineral wool, sealants, adhe-
sives, and TPO membranes dominate the impacts.
The total environmental impact of the concrete
building is dominated by Division 03, consisting
of concrete and rebar, which accounts for 72%,
72%, 61%, and 86% in the impact categories of
global warming, smog, acidication, and eutro-
phication, respectively. These numbers range
Figure 4. Normalized impacts (A1-A3) from different building sections for mass timber (left column) and concrete (right
column) buildings.
from 17% to 50% for the mass timber building.
Approximately 58% concrete and 72% rebar
in Division 03 of the concrete building are
substituted by 2339 m
CLT and glulam in Di-
vision 06 for the mass timber building, which
resulted in Division 06 in the mass timber
building contributing 28%, 49%, 45%, and 22%
to the impact categories of global warming, smog,
acidication, and eutrophication, respectively.
The two buildings have no signicant differences
in Division 07. In addition, in the mass timber
building, Division 09 contributes relatively more
to all impact categories than it does in the con-
crete building, which is largely caused by the use
of 36% more gypsum board in the mass timber
building compared with the concrete building.
Carbon Analysis
Biogenic carbon refers to CO
emissions that
originate from biological sources such as plants,
trees, and soil (Harris et al 2018). In LCA studies
of durable wood products, it is assumed that
harvested timber products will be replaced sus-
tainably by new growth in managed forest land,
and therefore, the biogenic CO
emissions are
considered to be carbon neutral from the climate
change prospective. The Intergovernmental Panel
on Climate Change (IPCC 2006) also supports
the carbon neutral hypothesis, which considers
the CO
emissions from biomass as part of the
natural carbon cycle. The carbon in wood is
accounted for as stored CO
during the lifetime of
the product or building. Such stored carbon is
estimated by average carbon content of 50% of
dry mass of wood products. This analysis as-
sumed a service life of 100 yr for the mass timber
building, which equates to the same time frame
used for accounting for GHG emissions in this
study. As shown by this LCI analysis and Fig 6,
biogenic CO
emissions from the mass timber
and concrete buildings were 81 and 3.4 kg/m
oor area, respectively. These results were
closely aligned with the consumption of renew-
able energy in the two building types. The
Figure 6. Comparison of CO
emissions for mass timber
and concrete buildings under different carbon accountings.
Figure 5. Normalized impacts (A1-A3) of different construction divisions for mass timber (left column) and concrete (right
column) buildings.
sequestered CO
values in wood products were
about 276 and 4.3 kg/m
of oor area for the mass
timber and concrete buildings, respectively. As
previously calculated, the GHG emissions for the
CLT and concrete buildings were 193 and 237 kg
of oor area, respectively, which is
about 18% different. More signicant differences
were observed when biogenic carbon and se-
questered carbon were combined, resulting in
values of CO
emissions for the mass timber and
concrete buildings of 2.7 and 236 kg/m
of oor
area, respectively.
Sensitivity Analysis
Transportation accounts for about 5% of the total
global warming impact emissions for the mass
timber building. But given that there is a limited
production infrastructure for CLT, it is worth
considering the effects of different production/
transportation alternatives on the overall global
warming impacts of the building. CLT trans-
portation has a global warming impact of 3.4 kg
of oor area when assuming local
production and transportation (320 km). Thus,
with limited CLT production in the United States,
it is important to understand the implication of
longer transportation distances. Figure 7 shows
the global warming impacts of different CLT
transport distances and, specically, the effects of
sourcing CLT from INW, the eastern United
States, or Europe. This analysis shows that the
global warming impact of CLT transportation
increased from 3.4 to 8.2, to 16, to 47 kg CO
of oor area with the increasing levels of
distance, respectively (Fig 7), which also ac-
counts for 59%, 73%, and 89% of total impacts in
the transport phase (module A4) for the three
projected regions. Meanwhile, as shown in Fig 7,
the transport phase (module A4) contributes less
than 5% to the global warming impact compared
with the module A1-A5 impacts under the local
(within 320 km) assumption, and this ratio would
increase to 7%, 10%, and 22%, respectively, if
sourcing the CLT material from the three other
The CLT transport distance revealed substantial
changes to the differences between the mass
timber and concrete buildings in environmental
impacts. The mass timber building outperformed
the concrete building inglobal warming with 18%,
16%, and 13% lower impacts when sourcing from
local and projected INW and eastern US regions.
However, the mass timber building had 0.2%
higher global warming impact than the concrete
Figure 7. Global warming impacts from transportation of cross-laminated timber (CLT) materials to the building site
(assuming CLT manufacturer in-state with a distance of 375 miles; INW: Inland Northwest region in the United States,
Eastern: eastern United States, and Oversea: Europe) and the fraction of A4 impact in total A1-A5 for the mass timber building.
building if CLT was sourced from Europe because
of the long transportation distance.
Study Strengths and Limitations
A strength of this study was the detailed building
design information for two equivalent buildings
by our highly qualied architectural and struc-
tural engineering partners. The study evaluated
the structural elements, modules A1-A5, with the
expectations that the bill of the materials for the
two buildings incorporated the same U-value.
Although mineral wool was incorporated into the
analysis at the same quantities, its impacts were
less than 0.3%. A limitation of this study was the
lack of detail on the CLT manufacturing process.
This lack of detail includes energy consumption
in the manufacturing, proprietary details such as
resin use, and the yield of CLT from dimensional
lumber. In this study, the building components
were limited to elements that were most different,
eg the ceilings-roof, oors, foundation, post-
beams, and walls. Other equivalent components
such as windows, doors, plumbing, and elec-
tricity were excluded in the scope of this study.
Construction site data including equipment use,
electricity use, and labor count were not available
for this study. Therefore, an empirical equation
provided by the Athena Sustainable Materials
Institute and based on building height was used.
As with any LCA, additional data on specic
processes, eg CLT manufacturing to concrete
transportation, will improve the value of the
In this study, a comparative cradle-to-site LCA of
a mass timber, tall wood building, and a func-
tionally equivalent concrete building was con-
ducted. This study shows that the mass timber
building outperformed the concrete building on a
number of environmental impact categories, eg
global warming, ozone depletion, and eutrophi-
cation, whereas the concrete building showed
better performance on smog and acidication, as
well as total primary energy demand. The product
phase (modules A1-A3) contributed more than
66% of total cradle-to-site (modules A1-A5)
impacts in all impact categories for both build-
ings. The mass timber building was much lighter,
68% of the total weight of the concrete building.
Even with the use of concrete and steel in the
foundation and CLT oor systems, the mass
timber building used 58% of the concrete and
72% of the rebar of the concrete building. Floors
and walls were major environmental contributors
in building sections. CLT and concrete were the
hotspot for the tall wood building, and concrete
and rebar were the hotspot for the concrete
building. The required use of more gypsum board
for mid- to high-rise mass timber buildings to
comply with building codes increased global
warming, smog, acidication, and eutrophica-
tion. The CLT building had lower CO
than the concrete building when biogenic carbon
and sequestered carbon were included. Sensi-
tivity analysis showed that the environmental
impacts for CLT transport distance, including
sourcing from European countries, could reverse
the advantages of all impact categories for the
mass timber building in this study. Further work
will focus on environmental impacts at the use
and end-of-life phases.
This project was nancially supported by a joint
venture agreement between the USDA Forest
Service, Forest Products Laboratory, and the U.S.
Endowment for Forestry & Communities, Inc.,
Endowment Green Building PartnershipPhase
1, no. 16-JV-11111137-094. External reviews
were performed by Jonathan Heppner, Lever
Architecture; Cindy Chen and Francesca Pier-
obon, University of Washington; and Kuma
Sumathipala, American Wood Council. The au-
thors also acknowledge the anonymous reviewers
from the Wood and Fiber Science journal.
APA (2012) ANSI/APA PRG 320-2012 Standard for
performance-rated cross-laminated timber. APA The
Engineered Wood Association, Tacoma, WA.
APA (2019) Case study: Mass timber has banks seeing green.¼Massþ
tember 2019).
ASTM (2016) ASTM E2911: Practice for minimum criteria
for comparing whole building life cycle assessments for
use with building codes, standards, and rating systems.
American Society for Testing and Materials, West Con-
shohocken, PA.
Bare J, Young D, Hopton M (2012) Tool for the reduction
and assessment of chemical and other environmental
impacts 2.1. STD Standard Operating Procedure (SOP)
SOP No. S-10637-OP-1-0.
Berardi U (2017) A cross-country comparison of the building
energy consumptions and their trends. Resour Conserv
Recycl. 123:230-241.
Bowers T, Puettmann ME, Ganguly I, Eastin I (2017) Cradle-
to-gate life-cycle impact analysis of glued-laminated
(glulam) timber: Environmental impacts from glulam
produced in the US Pacic northwest and southeast. For
Prod J 67(5-6):368-380.
Bowick M (2015) Wood innovation and design centre Prince
George, BC: An environmental building declaration
according to EN 15978 standard. Athena Sustainable
Materials Institute, Ottawa, ON, Canada. pp. 1-54.
Bowick M (2018) Athena Brock Commons Tallwood House,
University of British Columbia: An environmental
building declaration according to EN 15978 standard.
Athena Sustainable Materials Institute, Ottawa, ON,
Canada. pp. 1-55.
Breneman S, Richardson D (2019) Tall wood buildings and
the 2021 IBC: Up to 18 stories of mass timber. WW-WSP-
12. Wood Works. pp. 1-11.
Cadorel X, Crawford R (2018) Life cycle analysis of cross
laminated timber in buildings: A review. Pages 107-114 in
Engaging Architectural Science: Meeting the Challenges
of Higher Density: 52nd International Conference of the
Architectural Science Association and RMIT University,
Melbourne, VIC, Australia.
Chen CX, Pierobon F, Ganguly I (2019) Life cycle assess-
ment (LCA) of cross-laminated timber (CLT) produced in
western Washington: The role of logistics and wood
species mix. Sustainability 11:1278.
Connolly T, Loss C, Iqbal A, Tannert T (2018) Feasibility
study of mass-timber cores for the UBC tall wood building.
Buildings 8:98.
CSI (2016) MasterFormat 2016. Construction Specications
Institute (CSI), Alexandria, VA.
DATASMART 2019. LCI package (US-EI SimaPro
life-cycle-inventory/ (26 March 2020).
Durlinger B, Crossin E, Wong J (2013) Life cycle assessment
of a cross laminated timber building. Forest & Wood
Products Australia, Melbourne, VIC, Australia. ISBN:
978-1-921763-63-2, pp. 1-110.
EN (2011) EN 15978: Sustainability of construction works -
Assessment of environmental performance of buildings -
Calculation method. European Committee for Standardi-
zation, Brussels, Belgium.
Espinoza O, Buehlmann U (2018) Cross-laminated timber in
the USA: Opportunity for hardwoods? Curr For Rep 4:
FII (2016) Brock Commons Tallwood House. Forestry innovation
investment (FII), naturally: Wood. https://www.naturallywood.
house (17 July 2019).
Finlayson G (2019) Personal communication. Athena
Grann B (2013) A comparative life cycle assessment of two
multistory residential buildings: Cross-laminated timber vs.
concrete slab and column with light gauge steel walls.
FPInnovations Report, Vancouver, BC, Canada. pp. 1-121.
Gu H, Bergman R (2018) Life cycle assessment and envi-
ronmental building declaration for the design building at
the University of Massachusetts. General Technical Report
FPL-GTR-255. U.S. Department of Agriculture, Forest
Service, Forest Products Laboratory, Madison, WI. 71 pp.
Gustavsson L, Joelsson A, Sathre R (2010) Life cycle pri-
mary energy use and carbon emission of an eight-storey
wood-framed apartment building. Energy Build 42(2):
Harris ZM, Milner S, Taylor G (2018) Biogenic carbon
Capture and sequestration. In Greenhouse Gas Balances of
Bioenergy Systems, Chapter 5. Academic Press, Cam-
bridge, MA. pp. 55-76.
Heppner J (2019) Personal communication. LEVER
Huijbregts MA, Rombouts LJ, Hellweg S, Frischknecht R,
Hendriks AJ, van de Meent D, Ragas AM, Reijnders L,
Struijs J (2006) Is cumulative fossil energy demand a
useful indicator for the environmental performance of
products? Environ Sci Technol 40(3):641-648.
IPCC (2006) Guidelines for national greenhouse gas in-
ventories. Institute for Global Environmental Strategies
(IGES) for the IPCC, Kanagawa, Japan.
ISO (2006a) ISO 14040: Environmental management Life
cycle assessment Principles and framework. International
Organization for Standardization, Geneva, Switzerland.
ISO (2006b) ISO 14044: Environmental management Life cycle
assessment Requirement and guidelines. International Or-
ganization for Standardization, Geneva, Switzerland.
Jones K, Stegemann J, Sykes J, Winslow P (2016) Adoption
of unconventional approaches in construction: The case of
cross-laminated timber. Constr Build Mater 125:690-702.
Karacabeyli B, Douglas B (2013) CLT Handbook, US
2013_gagnon001.pdf (17 July 2019).
Kelley S, Bergman R (2017) Potential for tall wood buildings to
sequester carbon, support forest communities, and create new
options for forest management. Forest Products Laboratory
Research in Progress.
(26 March 2020).
Kremer PD, Symmons MA (2015) Mass timber construction
as an alternative to concrete and steel in the Australia
building industry: A PESTEL evaluation of the potential.
Int Wood Prod J 6(3):138-147.
Oregon BEST (2017) Advanced wood product manufacturing
study for cross-laminated timber acceleration in Oregon &
SW Washington. Technical Report. Oregon BEST, Port-
land, OR. pp. 1-111.
Perez-Garcia J, Lippke B, Briggs D, Wilson JB, Bowyer J,
Meil J (2005) The environmental performance of renew-
able building materials in the context of residential con-
struction. Wood Fiber Sci 37:3-17.
Pierobon F, Huang M, Simonen K, Ganguly I (2019) En-
vironmental benets of using hybrid CLT structure in
midrise non-residential construction: An LCA based
comparative case study in the US PNW. J Build Eng 26:
Podesto L, Berneman S (2016) CLT research: Available and
accessible to North American building designers. Wood
Design Focus 26(1):3-7.
Ritter M, Skog K, Bergman R (2011) Science supporting the
economic and environmental benets of using wood and
wood products in green building construction. General
Technical Report FPL-GTR-206. U.S. Department of
Agriculture, Forest Service, Forest Products Laboratory,
Madison, WI. 9 pp.
Robertson AB, Lam FC, Cole R (2012) A comparative
cradle-to-gate life cycle assessment of mid-rise ofce
building construction alternatives: Laminated timber or
reinforced concrete. Buildings 2:245-270.
Smith RE, Grin G, Rice T, Hagehofer-Daniell B (2018)
Mass timber: Evaluating construction performance. Ar-
chitectural Engineering and Design Management 14(1-2):
Tecchio P, Gregory J, Olivetti E, Ghattas R, Kirchain R
(2018) Streamlining the life cycle assessment of buildings
by structured under-specication and probabilistic triage.
J Ind Ecol 23(1):268-279.
Walch F, Watts R (1923) Composite lumber. U.S. Patent
Williamson T, Ross R (2016) Proceedings: Mass timber
research workshop 2015. General Technical Report FPL-
GTR-241. U.S. Department of Agriculture, Forest Service,
Forest Products Laboratory, Madison, WI. 364 pp.
... The use of sustainably sourced mass-timber technologies to build multistory residential buildings (mainly cross-laminated timber (CLT) and glue-laminated timber (glulam)) has the potential to mitigate global climate change and benefit developing economies [1][2][3]. While it is well known that the building sector is responsible for about 40% of global carbon emissions [4], there is a large body of scientific research showing that, compared to reinforced concrete (RC), mass-timber (MT) buildings can store large amounts of biogenic carbon, reduce the embodied carbon of building materials, and avoid useful life emissions from auxiliary space-conditioning energy [5][6][7][8]. ...
... m 3 of processed mass-timber per square meter of floor area, a high usage rate compared to other studies in which usage rates are between 0.1-0.45 m 3 [3,38]. Other capital equipment and facilities, land use, maintenance, use, and final disposal were excluded from the system boundaries. ...
... In this stage, the global warming contribution of the MT design was 44% lower (90 kg CO2 eq/m 2 ) than that of the mainstream RC building (162 kg CO2 eq/m 2 ), attributable to the relatively high usage of mass timber and differences in national energy source mixes. This is a considerable cut in emissions compared to other studies that found reductions from RC to MT buildings in the order of 18% and 28%, with the embodied carbon of MT buildings ranging from 190-240 kg CO2 eq/m 2 [3,21]. ...
Full-text available
While high-rise mass-timber construction is booming worldwide as a more sustainable alternative to mainstream cement and steel, in South America, there are still many gaps to overcome regarding sourcing, design, and environmental performance. The aim of this study was to assess the carbon emission footprint of using mass-timber products to build a mid-rise low-energy residential building in central Chile (CCL). The design presented at a solar decathlon contest in Santiago was assessed through lifecycle analysis (LCA) and compared to an equivalent mainstream concrete building. Greenhouse gas emissions, expressed as global warming potential (GWP), from cradle-to-usage over a 50-year life span, were lower for the timber design, with 131 kg CO2 eq/m2 of floor area (compared to 353 kg CO2 eq/m2) and a biogenic carbon storage of 447 tons of CO2 eq/m2 based on sustainable forestry practices. From cradle-to-construction, the embodied emissions of the mass-timber building were 42% lower (101 kg CO2 eq/m2) than those of the equivalent concrete building (167 kg CO2 eq/m2). The embodied energy of the mass-timber building was 37% higher than that of its equivalent concrete building and its envelope design helped reduce space-conditioning emissions by as much as 83%, from 187 kg CO2 eq/m2 as estimated for the equivalent concrete building to 31 kg CO2 eq/m2 50-yr. Overall, provided that further efforts are made to address residual energy end-uses and end-of-life waste management options, the use of mass-timber products offers a promising potential in CCL for delivering zero carbon residential multistory buildings.
... CLT construction offers structural, economic, and environmental benefits with respect to traditional building materials (concrete, steel, and masonry). As an engineered timber-based material it provides better life cycle environmental performance (Pierobon et al. 2019;Liang et al. 2020;Jayalath et al. 2020) and less waste and pollution generation ). Besides, the high level of prefabrication and lightweight of the CLT components provide faster erection times and easier on-site handling (APA 2019). ...
... With regard to construction costs, CLT buildings are economically competitive in the medium to high-rise segment (Pei et al. 2016), but for low-rise buildings, the cost tends to be higher (Burback and Pei 2017;Ahmed and Arocho 2021). However, considering the total life cycle cost, CLT buildings have advantages if long life spans are considered (Gu et al. 2020). ...
Full-text available
The CLT market is quickly growing and developing in different regions of the world. However, the production and consumption are highly concentrated in Central Europe (Austria, Germany, Italy, and Switzerland). Due to the elevated levels of personalization required for the construction projects, the CLT manufacturing process involves costly and specialized equipment that represents an entry barrier for domestic producers in markets where the demand is small and incipient. This work discusses a production model and supply chain integration for the development of the CLT industry in emerging environments where the product and its properties are not well-known. Furthermore, a comprehensive economic analysis is performed for three small capacity mills designed according to SMEs capabilities. Findings suggest that CLT manufacturing with low-capacity plants (less than 10,000 m³/yr) is profitable but high levels of integration are required. The most influential variables in the economic results are the lumber cost and production volume; therefore, special attention must be paid to the efficiency of the process. Despite the small size of the studied plants promoted by the proposed production and plant design model, the sale price is attractive and competitive.
... Timber is a good alternative to concrete and steel as a construction material, due to the high strength/weight ratio. Comparative life cycle analysis (LCA) studies highlight the positive environmental impact of using cross laminated timber (CLT) instead of reinforced concrete in multistorey buildings [4][5][6][7][8][9]. Skullestad et al. [10] performed LCA on buildings up to 21 floors and concluded that timber buildings have 34-84% lower climate change impact than reinforced concrete buildings with the same load capacity. ...
... Previous studies have shown that using timber as a construction material instead of structural steel or reinforced concrete can result in reduced GHG emissions and, therefore, more environmentally friendly construction [4][5][6][7][8][9][10][11][12][13][14]. However, the focus was mainly on multistorey residential buildings, and less focus was given to industrial buildings. ...
Full-text available
The construction industry is a big contributor to greenhouse gas emissions, which has a negative environmental impact. Several studies have highlighted the possibility of using timber to reduce the environmental impact of construction. Most of these studies have focused on residential buildings, but little attention has been devoted to industrial buildings. In this paper, an attempt is made to compare the environmental impact of using timber, steel, and reinforced concrete in industrial buildings using life cycle assessment. The system boundary was set to cradle-to-gate with transportation to construction site due to the limitation of data, and only the quantities of the main structural system are considered. Portal frames with variable spans were designed using the three materials to meet similar load carrying capacity. Reinforced concrete was used in the foundation of all frames. The results of the comparative study show that timber has, by a good margin, better environmental impact than reinforced concrete and steel, due to the carbon stored in the wood. The results also show that reinforced concrete and steel alternatives have similar environmental impacts. The findings of this study agree with the findings of other studies on residential buildings.
... A growth of the global share of timber construction in the building industry has been observed in the past years. Rising order numbers, due to the positive environmental properties of timber among other reasons, and the growing complexity of construction projects, has resulted in the need for an increase in production efficiency by, for example, evaluating new manufacturing methods (Liang et al. 2020). ...
With the growing demand for timber construction, more advanced production methods need to be developed and applied. Multi-axis industrial robots (IR) show a high potential for increasing the efficiency and extending the workspace within subtractive manufacturing. To apply IRs, it is necessary to understand the interaction between the robot and the mechanics of machining and reveal optimal settings. This study investigates the effects of machining parameters (axial and radial depth of cut) and robot kinematic settings (acceleration, jerk) using typical milling tools for the machining of elementary geometries (lines, rings, pockets). The results are evaluated based on the surface finish (tactile measurements and optical/haptic assessment) and nominal/actual comparison of the geometry. Axial and radial depth of cut is high relevance: higher values lead to lower quality while mid-range settings frequently lead to the highest quality. The robot's kinematic settings have higher effects when using relatively small diameter tools. The tool manufacturers feed recommendations for CNC-machines are also applicable to robot machining and all examined parameters are relevant factors influencing the quality. The results achieved with the IR can compete with conventional joinery machines and are able to meet the currently required industry standards with further potential for improvement.
... The construction phase of timber buildings can deliver considerable savings with over 50% faster assembly times compared to traditional construction materials [51]. Timber construction offers light and prefabricated alternatives with various size and thermal insulation options to respond to special demands [52][53][54]. ...
Full-text available
One of the most effective ways to cover real estate development and renovation processes by improving functionality and energy efficiency is wooden additional floor construction. This entry maps out, organizes, and collates scattered information on the current state of the art and the benefits of this practice including its different stages, focusing on the case of Finland. The entry presents this topic in an accessible and understandable discourse for non-technical readers. By highlighting the benefits and opportunities of this sustainable application, the entry will contribute to increasing the awareness of wooden additional floor construction, which has many advantages, and therefore to gain more widespread use in Finland and other countries.
... Several recent studies have shown that substituting mass timber for steel and concrete in mid-rise buildings can reduce the emissions associated with manufacturing, transporting, and installing building materials by 13-26.5% [5][6][7]. Other studies have quantified the amount of carbon stored in mass timber materials themselves, which persists for the useful life of the building and perhaps longer if materials are recovered, reused or repurposed [8]. ...
Full-text available
As the need to address climate change grows more urgent, policymakers, businesses, and others are seeking innovative approaches to remove carbon dioxide emissions from the atmosphere and decarbonize hard-to-abate sectors. Forests can play a role in reducing atmospheric carbon. However, there is disagreement over whether forests are most effective in reducing carbon emissions when left alone versus managed for sustainable harvesting and wood product production. Cross-laminated timber is at the forefront of the mass timber movement, which is enabling designers, engineers, and other stakeholders to build taller wood buildings. Several recent studies have shown that substituting mass timber for steel and concrete in mid-rise buildings can reduce the emissions associated with manufacturing, transporting, and installing building materials by 13%-26.5%. However, the prospect of increased utilization of wood products as a climate solution also raises questions about the impact of increased demand for wood on forest carbon stocks, on forest condition, and on the provision of the many other critical social and environmental benefits that healthy forests can provide. A holistic assessment of the total climate impact of forest product demand across product substitution, carbon storage in materials, current and future forest carbon stock, and forest area and condition is challenging, but it is important to understand the impact of increased mass timber utilization on forests and climate, and therefore also on which safeguards might be necessary to ensure positive outcomes. To thus assess the potential impacts, both positive and negative, of greater mass timber utilization on forests ecosystems and emissions associated with the built environment, The Nature Conservancy (TNC) initiated a global mass timber impact assessment (GMTIA), a five-part, highly collaborative research program focused on understanding the potential benefits and risks of increased demand for mass timber products on forests and identifying appropriate safeguards to ensure positive outcomes.
... The results showed the total amount of pollution by the RC building at various stages was 38% higher than by the steel building, and the steel frame selection in RC buildings was more environmentally friendly than the building industry concrete frame. Liang et al. [73] made a comparative LCA of a 12-story mixed-use building constructed predominantly from solid timber (CLT and glulam) and a similar concrete building. The results indicated that the solid timber building had reductions of 18%, 1%, and 47% in the global warming, ozone depletion, and eutrophication impact categories, respectively, and the use of solid timber significantly reduced the carbon footprint of the building. ...
Full-text available
To date, in the literature, there has been no study on the comparison of hybrid (timber and concrete) buildings with counterparts made of timber and concrete as the most common construction materials, in terms of the life cycle assessment (LCA) and the carbon footprint. This paper examines the environmental impacts of a five-story hybrid apartment building compared to timber and reinforced concrete counterparts in whole-building life-cycle assessment using the software tool, One Click LCA, for the estimation of environmental impacts from building materials of assemblies, construction, and building end-of-life treatment of 50 years in Finland. Following EN 15978, stages of product and construction (A1–A5), use (B1–B6), end-of-life (C1–C4), and beyond the building life cycle (D) were assessed. The main findings highlighted are as following: (1) for A1–A3, the timber apartment had the smallest carbon footprint (28% less than the hybrid apartment); (2) in A4, the timber apartment had a much smaller carbon footprint (55% less than the hybrid apartment), and the hybrid apartment had a smaller carbon footprint (19%) than the concrete apartment; (3) for B1–B5, the carbon footprint of the timber apartment was larger (>20%); (4) in C1–C4, the carbon footprint of the concrete apartment had the lowest emissions (35,061 kg CO2-e), and the timber apartment had the highest (44,627 kg CO2-e), but in D, timber became the most advantageous material; (5) the share of life-cycle emissions from building services was very significant. Considering the environmental performance of hybrid construction as well as its other advantages over timber, wood-based hybrid solutions can lead to more rational use of wood, encouraging the development of more efficient buildings. In the long run, this will result in a higher proportion of wood in buildings, which will be beneficial for living conditions, the environment, and the society in general.
Life cycle assessment (LCA) has been widely used to investigate the environmental performance of building developments. However, LCA studies on the construction stage emissions are limited due to its relatively minor impacts in a building life cycle. In view of the continual advancement in energy efficiency and building services, reducing carbon emissions from the construction activities will become more important. Such emission reduction is particularly crucial for wooden construction because reductions in these anthropogenic carbon emissions can enhance the utility of biogenic carbon sequestration and reduce the distance to carbon flux neutrality. This study applies LCA to a wooden construction to evaluate the anthropogenic carbon emissions from the material extraction, production, transportation, and particularly the construction stage. LCA data disaggregation is adopted to identify the unnoticed emission hotspots, contexts of the occurrence, and countermeasures against the underperformance for individual processes. The findings highlight that concrete foundation works of wooden constructions can contribute significantly to not only embodied carbon but also construction carbon emissions, and suggest courses of action for wooden constructions to reduce the anthropogenic carbon emissions. Future research should enrich the disaggregated LCA data for inter-referencing sustainable strategies to reduce the anthropogenic carbon emissions throughout the building life cycle.
Full-text available
The building industry is a large contributor to greenhouse gas (GHG) emissions and a vast consumer of natural resources. It is estimated that, in the next 40 years, around 415 Gt of CO2 will be released as a result of global construction activities. Therefore, improvements in construction technologies are essential to reduce GHG emissions and thereby attain national and international goals to mitigate climate change. Cross-laminated timber (CLT) has emerged as an innovative alternative material to steel/concrete in building construction, given its relatively low carbon footprint, not to mention its high strength-to-weight ratio, simple installation, and aesthetic features. CLT is a structural composite panel product developed in the early 1990s, and the contemporary generation of CLT buildings are yet to reach the end of their service life. Accordingly, there has been growing interest to understand and optimize the performance of CLT in building construction. In view of that, this paper presents an overview on the feasibility of using CLT in buildings from a life-cycle assessment (LCA) standpoint. The authors performed a brief review on LCA studies conducted in the past decade pertaining to the carbon footprint of CLT buildings. On average, the findings of these studies revealed about 40% reduction in carbon footprint when using CLT in lieu of conventional construction materials (steel/concrete) for multi-story buildings. Furthermore, the paper explores the challenges associated with conducting LCA on CLT buildings, identifies the gaps in knowledge, and outlines directions for future research.
Full-text available
Universities, as innovation drivers in science and technology worldwide, should attempt to become carbon-neutral institutions and should lead this transformation. Many universities have picked up the challenge and quantified their carbon footprints; however, up-to-date quantification is limited to use-phase emissions. So far, data on embodied impacts of university campus infrastructure are missing, which prevents us from evaluating their life cycle costs. In this paper, we quantify the embodied impacts of two university campuses of very different sizes and climate zones: the Umwelt Campus Birkenfeld (UCB), Germany, and the Nanyang Technological University (NTU), Singapore. We also quantify the effects of switching to full renewable energy supply on the carbon footprint of a university campus based on the example of UCB. The embodied impacts amount to 13.7 (UCB) and 26.2 (NTU) kg CO2e/m2•y, respectively, equivalent to 59.2% (UCB), and 29.8% (NTU), respectively, of the building lifecycle impacts. As a consequence, embodied impacts can be dominating; thus, they should be quantified and reported. When adding additional use-phase impacts caused by the universities on top of the building lifecycle impacts (e.g., mobility impacts), both institutions happen to exhibit very similar emissions with 124.5–126.3 kg CO2e/m2•y despite their different sizes, structures, and locations. Embodied impacts comprise 11.0–20.8% of the total impacts at the two universities. In conclusion, efficient reduction in university carbon footprints requires a holistic approach, considering all impacts caused on and by a campus including upstream effects.
Full-text available
The use of cross-laminated timber (CLT), as an environmentally sustainable building material, has generated significant interest among the wood products industry, architects and policy makers in Washington State. However, the environmental impacts of CLT panels can vary significantly depending on material logistics and wood species mix. This study developed a regionally specific cradle-to-gate life cycle assessment of CLT produced in western Washington. Specifically, this study focused on transportation logistics, mill location, and relevant wood species mixes to provide a comparative analysis for CLT produced in the region. For this study, five sawmills (potential lamstock suppliers) in western Washington were selected along with two hypothetical CLT mills. The results show that the location of lumber suppliers, in reference to the CLT manufacturing facilities, and the wood species mix are important factors in determining the total environmental impacts of the CLT production. Additionally, changing wood species used for lumber from a heavier species such as Douglas-fir (Pseudotsuga menziesii) to a lighter species such as Sitka spruce (Picea sitchensis) could generate significant reduction in the global warming potential (GWP) of CLT. Given the size and location of the CLT manufacturing facilities, the mills can achieve up to 14% reduction in the overall GWP of the CLT panels by sourcing the lumber locally and using lighter wood species.
Conference Paper
Full-text available
Greenhouse gas (GHG) emissions have increased for the last three consecutive years in Australia, and this directly threatens our ability to meet our 2030 GHG emission reduction target under the Paris Agreement. Despite progress in reducing building-related GHG emissions, little focus has been placed on the indirect GHG emissions associated with building material manufacture, and construction. Cross laminated timber (CLT) is an alternative construction material that has been subject to numerous comparison studies, including many life cycle assessments (LCA). The aim of this paper is to provide a review of the recent literature on the environmental performance of CLT construction for Medium Density Residential (MDR) buildings and to identify knowledge gaps that require further research. Studies reviewed were sourced from web-based research engine, direct searches on global wood promotion websites, and the review was limited to peer reviewed publications. This review provides a useful basis for informing the exploration of important gaps in the current knowledge of how CLT buildings perform from an environmental perspective. This will ensure a comprehensive understanding of the environmental benefits of CLT construction and inform decision-making relating to structural material selection for optimising the life cycle GHG emissions performance of buildings.
Full-text available
The UBC Brock Commons building in Vancouver, which comprises of 18 stories and stands 53 m in height, was at the time of completion in 2016 the world’s tallest hybrid wood-based building. The building’s 17 stories of mass-timber superstructure, carrying all gravity loads, rest on a concrete podium with two concrete cores that act as both the wind and seismic lateral load-resisting systems. Whereas the construction of the concrete cores took fourteen weeks in time, the mass-timber superstructure took only ten weeks from initiation to completion. A substantial reduction in the project timeline could have been achieved if mass-timber had been used for the cores, leading to a further reduction of the building’s environmental footprint and potential cost savings. The objective of this research was to evaluate the possibility of designing the UBC Brock Commons building using mass-timber cores. The results from a validated numerical structural model indicate that applying a series of structural adjustments, that is, configuration and thickness of cores, solutions with mass-timber cores can meet the seismic and wind performance criteria as per the current National Building Code of Canada. Specifically, the findings suggest the adoption of laminated-veneer lumber cores with supplementary ‘C-shaped’ walls to reduce torsion and optimize section’s mechanical properties. Furthermore, a life cycle analysis showed the environmental benefit of these all-wood solutions.
Full-text available
Purpose of Review In this paper, the authors review the available literature on the manufacture and usage of hardwood cross-laminated timber (CLT) and discuss the technical and economic feasibility of hardwood CLT including procurement issues. Recent Findings CLT is an emerging building system in North America that has attracted the attention of construction professionals, developers, and researchers across the continent, due to its environmental, economic, and esthetic advantages, among others. Today, however, virtually all CLT structures are manufactured using softwoods, yet, there is growing interest in the possibility of manufacturing CLT using a variety of hardwood species. To date, most studies on the feasibility of hardwood CLT are motivated by a desire to find high value-added uses for underutilized or low-valued hardwood species but there is also an interest in benefitting of specific mechanical properties of selected hardwood species. Summary Research on hardwood CLT is scarce, though findings from existing studies suggest that it is technically feasible and the resulting product offers interesting perspectives for specific applications. However, for hardwood CLT to become a reality, the hardwood industry needs to overcome significant challenges, some of which are discussed in this paper.
Full-text available
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.
In this study, the cradle-to-gate environmental impact of a hybrid, mid-rise, cross-laminated timber (CLT) commercial building is evaluated and compared to that of a reinforced concrete building with similar functional characteristics. This study evaluates the embodied emissions and energy associated with building materials, manufacturing, and construction. Two alternative designs are considered for fire protection in the hybrid CLT building: 1) a ‘fireproofing design’, where gypsum wallboard is applied to the structural wood; and 2) a ‘charring design’, where two extra layers of CLT are added to the panel. The life cycle environmental impacts are assessed using TRACI 2.1 and the total primary energy is evaluated using the Cumulative Energy Demand impact method. Results show that an average of 26.5% reduction in the global warming potential is achieved in the hybrid CLT building compared to the concrete building, excluding biogenic carbon emissions. Except ozone depletion, where the difference in impact between scenarios is <1%, replacing fireproofing with charring is beneficial for all impact categories. The embodied energy assessment of the building types reveals that, on average, the total primary energy in the hybrid CLT buildings and concrete building are similar. However, the non-renewable energy (fossil-based) use in the hybrid CLT building is 8% lower compared to that of the concrete building. As compared to the concrete building, additional 1,556 tCO2e and 2,567 tCO2e are stored in the wood components of the building (long-term storage of biogenic carbon) in the scenario with fireproofing and with charring, respectively.
Life cycle thinking plays an important role in sustainable development in the building sector. However, the complexity of data collection and scope definition limits life cycle assessment (LCA) applications. Even if the inventory data have already been collected, tabulated, and indexed, the method is still time-consuming, which may be discouraging for designers. This study demonstrates how the LCA of buildings can be robustly streamlined using structured underspecification of impact data combined with an effective and efficient triage of the data collection. Tests were conducted with a series of building typologies that were analyzed with a cradle-to-gate approach. The probabilistic triage approach was tested to identify selected activities requiring detailed specification because they contribute most to total impact, thereby reducing data gathering effort. Impacts such as global warming, acidification, eutrophication, and smog creation were assessed, and results showed that 40% to 46% of the bill of materials components represent 75% of total impacts of single-family houses and multifamily buildings. By specifying only a prioritized subset of the bill of materials to the highest level of specificity, results proved to be reasonably accurate and obtainable with less effort.
Biogenic carbon emissions are those that originate from biological sources such as plants, trees, and soil. Biogenic carbon emissions relate to the natural carbon cycle and there is significant interest in quantifying how plants capture CO2 in the process of photosynthesis, how it is lost in respiration and stored in biomass (both living and dead), and finally biologically sequestered into long-term biological stores in the soil. This biogenic terrestrial carbon cycle offers significant potential for greenhouse gas emissions (GHG) reductions and here we summarise findings for the major bioenergy crops, for biogenic carbon fluxes, and stores that contribute to biological carbon sequestration. The quantification of biogenic carbon in recent years has proved to be a highly controversial topic, since this stored carbon is used in national GHG inventories and in estimating whether bioenergy crops are sustainable.
Achieving sustainable development requires the decoupling of economic growth from the use of non-renewable resources. This depends on industry adopting unconventional approaches to production. This research explores the root causes of barriers to the adoption of such approaches in the construction industry, and applies a behavioural model to assess whether companies are hindered by capability, opportunity or motivation. The long history of lowest-cost tendering in construction has led to a path-dependent lock-in to conventional market-driven objectives of cost and risk reduction; it is suggested that locked-in companies lack the commercial opportunity and hence motivation, rather than the capability, to adopt approaches perceived to increase cost or risk. Such companies will therefore tend to resist unconventional approaches, restricting the physical opportunity for other project participants. This theory is explored in a case study of first adoptions of cross-laminated timber (CLT) in UK projects, using a survey and series of semi-structured interviews. The case study found that project contexts created market niches. This provided designers, who were motivated to use CLT, the opportunity to promote its use in the project. CLT was seen as key to successful resolution of project constraints, thereby providing motivation to other project participants to adopt the material.
Although it is often stated that the energy consumption in buildings accounts for more than 30% of total global final energy use, only a few studies analyze updated data about the current building energy consumptions or focus on comparing different countries. Similarly, models that predict future trends in building energy demand often use contrasting algorithms which result in diverse forecasts. Scope of this paper is to present and discuss data taken from several studies about the building energy consumptions in US, EU, and BRIC (Brazil, Russia, India, and China) countries and to provide an updated inventory of useful figures. Comparisons among countries are used to show historical, actual, and future energy consumption trends. Data presented by the World Bank, the United Nations Environment Program, the Intergovernmental Panel on Climate Change, and the International Energy Agency are compared with national reports as well as with research studies. The variety of the approaches used in each of the previous sources was considered fundamental to allow a complete review. The paper shows that the total building energy consumptions in BRIC countries have already overcome those in developed countries, and the continuous increase in the building stock of the BRIC countries creates an urgency for promoting building energy efficiency policies in these countries. At the same time, the policies actually adopted in developed countries are insufficient to guarantee a significant reduction in their building energy consumption in the years to come. In the current scenario, at least a doubling of the global energy demand in buildings compared to today’s levels will occur by 2050. To avoid this forecast, cost-effective best practices and technologies as well as behavioral and lifestyle changes need to be diffused and accepted globally.