In the field of construction, wood products are known to have environmental benefits in comparison with materials like steel and concrete, especially to mitigate climate change. Since wood is an anisotropic material, comparisons with other building materials on a volume functional unit basis, such as a cubic meter of product, are not relevant. Wood structures also allow for architectural forms that are not feasible with other building materials. To enable a comparison between wood and steel, we have assessed the Life Cycle Carbon Footprint of complete non-residential building structures. This building frame was initially planned to be made from steel, but the architecture was modified to integrate glued laminated timber beams. The structural engineers provided material balance changes. The results show a significant reduction in greenhouse gas emissions for structures using wood as a building material.
2. Keywords: Carbon Footprint; Life-Cycle Assessment; Non-Residential Buildings; Wood Buildings Material
In North America, wood components have always been
ubiquitous in the structure of residential buildings. Today, this wood culture
is maintained and renewed by the marketing of components or prefabricated
wooden frame houses. The situation is different in the nonresidential building
sector, such as institutional, commercial or industrial buildings. In the past
decade, less than 4% of non-residential buildings in North America were made of
wood . In lasts years this has increased to 10% but for FP Innovations there
is potential for at least a twofold increase in the use of wood for nonresidential
Several circumstances explain the low wood use in
nonresidential construction in North America. Between the 1930s and the 1970s,
modern architecture reinvented the design of public and commercial buildings, by
utilizing the properties of concrete and steel structures . This architectural
revolution has gradually led to the erosion of wood structures in
non-residential buildings . Indeed, from the beginning of the 20th
century only a few massive buildings were made from heavy timber (e.g. Butler
building (1906) in Minneapolis, MN or 320 Summer Street (1906) Boston, MA). It resulted
in a lack of knowledge about the potential of wood and engineered wood
products, as well as many misperceptions associated with the technical characteristics
of these structures. Thus, the expertise gradually vanished in the building
The development of new elements of wooden structures,
also called engineered wood, like glued laminated timber (glulam) or more
recently Cross-Lam Timber (CLT), have revitalized the wood building market. These
building systems make it possible for wood products to become economically
competitive. Nowadays, the costs of wooden structures are similar or lower compared
to steel or concrete structures . Another advantage is the speed of erection.
As the elements are pre-built in the factory, it remains only to assemble the
different pieces of structure on site, hence accelerating the time of construction
Among the presumed advantages of wood construction, it
is recognized that, in comparison with competing materials, the low carbon
emissions of the production line and the sequestration of CO2 in the
material during the whole life-span of the building may be integrated into a
climate change mitigation strategy . To compare the environmental impacts of
competitive building materials, Life Cycle Assessment (LCA) is commonly used .
The functional unit used in LCA usually is a surface area of building  or
volume or weight of materials . An easy method to calculate carbon
sequestration per cubic meter of wood products in a building is the use of the
“displacement factor” . This factor is an index to quantify the reduction of
Greenhouse Gas (GHG) emissions obtained per unit of wood products substituted
for non-wood products. A displacement factor of 2.1 tC/tC (metric tons of
carbon emission reduction per tC of additional wood products used) was
calculated by reviewing 66 studies around the world. However, other parameters
such as type of building, external climate, or architectural aesthetic design can
also affect the carbon footprint and this is not taken into account in the
displacement factor. Additionally, assessing mechanical properties of building
materials is complex and makes comparisons by physical unit (mass/volume) not
appropriate, since nonequivalent functions are then assessed. Mechanical resistance
is different if there is compressive (column) or bending (beam) strength for the
materials  and this affects the sizing (section) of the structural
components. Comparisons on a physical unit base are even more difficult, or not
possible, for other architectural elements like arches, since not every
building material can achieve such structure.
This study presents a detailed comparative assessment
of GHG emissions and carbon sequestration in a life-cycle approach of a hybrid structure
(made from wood and steel) and full steel frame for a non-residential building.
The aim is to calculate the carbon emissions reduction that can be achieved
with the use of wood material as a replacement for steel in a non-residential
building. The comparative scenarios were prepared for the same building and
were considered as building options for an arena located at the Université du
Québec à Chicoutimi (UQAC) campus (Saguenay, Quebec, Canada). It was actually
decided to choose to build the hybrid structure, which is presently fully functional
and for few decades. This assessment has the particularity of using
context-specific primary data. Indeed, the structural engineering company that
sized the steel and hybrid structures provided the calculated mass balance for
the design of the two structures. The calculation of wood impacts used a
cradle-to-gate LCA of a glulam company supplying arena beams . These data
were supplemented by field data collected during the construction of the arena.
The Life Cycle Carbon Footprint (LCCF) study is performed
in accordance to the ISO 14044 LCA guidelines . Therefore, the first section
is devoted to the definition of the objectives and scope of the study. It is
followed by the inventory analysis describing the sources and methodology used
in the data collection. In the third section, the impact assessment presents
the results of GHG emissions calculated from data inventories of both building
structures. Then the interpretation presents the analysis of uncertainty and
sensitivity as well as additional elements of discussion, all to draw
conclusions in the final section.
4. Definitions of the Objectives and
Scope of the System
Objectives and scope definition are the first step of the
presented LCA, according to the ISO 14040 series standards . It allows a
more elaborate approach than a carbon footprint based on the standard ISO 14067
, as the latter makes possible to calculate carbon footprint only related
to the direct emissions, also referred to as scope . The boundaries of this
study include all direct emissions, indirect emissions from energy and other
indirect emissions, also called scope 3.
4.1. Application Envisaged and Target
This study aims to assess the carbon footprint of
using wood components instead of steel components in a nonresidential
construction. It provides decision makers quantified arguments of the steel
substitution by wood to reduce greenhouse gas emissions and thus mitigate climate
change. The study will take advantage of a life cycle approach that avoids
shifting environmental impacts from one stage to another stage. However, this
study does apply to a region-specific context. The glulam is modelled from
primary data from the producer in Quebec, and the steel manufacturing is
representative for the North America market context. The model of the
construction stage is even specific for the building, since it was made from
the data collected on the construction site.
The results of the comparative study are relevant for
a wider audience interested in the use of wood in building structures to reduce
climate change impacts.
4.2. Functions and Functional Unit
The main function of the studied system is to support
the envelope of the UQAC arena during the lifetime of the building. The
structure of the building has multifunctional characteristics. Only the primary
function as support in the building was considered. The secondary functions of
this structure, like aesthetics and acoustic quality, are not considered. Since
aesthetics depend mostly on architects and is a subjective criterion and acoustic
aspects are not a priority for a sports venue. The functional unit for this
study is: "The structure of a non-residential building (an arena more
precisely), covering an area of 3780 m2 (or a volume of 23,000 m3),
for a life-span of 75 years".
Since this is an existing structure, the functional
unit includes the area and volume of the building, which provides the
opportunity to report the results to a physical allocation, in order to
calculate the displacement factor.
4.3. Reference Flow
The reference flow represents the quantity of products
necessary to fulfill the functional unit.
The lifetime of buildings in North America is not well
documented. Only one study from the Athena Institute was performed on 227 demolished
buildings, of which 94 were nonresidential. The results highlight the lack of
correlation between the materials used in a structure and the average life-span
of the building . Demolitions reasons recorded were economic or social but
less than one-third was demolished for physical failure. Those cases were
mainly related to fire damage and touched more steel than wood structures. The Athena
Institute study showed a longer lifetime expectation for wood nonresidential
buildings, in comparison to steel or concrete. The majority of wood buildings
reached 75 to 100 years but there are buildings that pass the 100 years
regardless of the building materials. A conservative point of view was taken in
the study in which it was assumed that the use of wood material in a nonresidential
construction does not require additional replacement or maintenance compared to
a steel construction. The reference flows for both types of structures were considered
identical for an expected life
span of 75 years. Both models include the quantity of materials needed to
support the envelope.
Product Systems and
The boundaries are
defined by the limits and the phases considered for the modeling of the system.
The comparative carbon footprint covers the entire life cycles of the two
building frames, thus a cradle-to-grave assessment. However, since it is a
comparative assessment, we chose to exclude the use phase assumed to be equivalent,
as further explained in the section general assumptions (Figure 1) shows the boundaries of the studied systems.
Activities Description: The resource extraction mainly covers the mining of iron ore
resources and the harvesting of wood resources. Resources are then transferred
to the transformation/production activity, which brings together the various
stages that take place at the processing and manufacturing sites of the two
construction materials studied. Data for extraction and production of the
various steel elements (hollow structural steel, flange sections, as well as screws
and bolts) are retrieved from the USLCI database (National Renewable Energy
Laboratory, Golden, Colorado) as these are representative for average North
American steel. The inventory includes a steel recycling rate of 76% . The data
for wood beam production are taken from the cradle to gate LCA study of Quebec
boreal forest glulam . This inventory is provided from the factory that produced
the glulam beams for the arena. It is important to note that both steel and
wood structures are preassembled at the factory. This includes other materials
(e.g. glues for the glulam beams), energy and
infrastructures dedicated to these transformations or productions.
materials are ready to be assembled, they are transported to the construction
site. Transportation of materials is done by truck, from Toronto (ON) for steel
and Chibougamau (QC) for glulam. The model includes an allocation of trucks and
road infrastructures to this activity.
Since the wood
structures are pre-assembled, the building activity consists of assembling the
beams together. The construction machines and the energy consumed are modeled.
The data are primary data taken on site during the construction of the hybrid
structure. The deconstruction activity inventory is modelled as identical to
the building activity, as further explained in section general assumptions.
The end-of-life activity
integrates the impacts of landfilling and building materials recycling,
including transportation and infrastructures. The end-of-life scenario is based
on the most recent statistical data representative of the construction sector
in the Saguenay-Lac-Saint-Jean (QC) area. Since it is difficult to know what
will happen in 75 years, during the
estimated deconstruction of the building, a sensitivity study on this scenario
is carried out in the results section to estimate the influence of this
scenario on the total carbon footprint. Non-landfilled wood, 2% according to ,
is modeled as a source of energy
4.5. Geographical Limits
boundaries of the study need to include the origin of all resources. The study
also needs to properly model activities that are different from region to
region, such as transportation, energy generation (electricity grid) and waste
management systems. Moreover, the sensitivity of the environment to different emissions
varies from one geographic zone to another.
To take account of
these geographical aspects, the databases used must be adapted as much as
possible. This study focuses on the harvesting, processing, production,
distribution, and end-of-life management in Quebec of a structure whose
components originate mainly from North America. Until 2007 Quebec's crude oil
supply came mainly from the North Sea and North Africa . To stick as much as possible to the local context an adjustment
was made based on the ecoinvent database (ecoinvent Centre, St-Gallen, Switzerland) inventories in Simapro
software V7.3 (PRé Consultants,
Amersfoort, The Netherlands).
4.6. Time Limits
The time period defined
by the functional unit corresponds to the useful life expectancy of the building
that is 75 years. Since the reference flow is the same for the two types of
structures studied, the temporal boundaries are defined for the estimated
lifetime of the building. It is important to note that:
processes can generate emissions over a long period. Landfilled organic
material, such as wood, may emit different GHGs over a very long period,
depending on the decomposition conditions. Some of these GHGs may or may not be
transformed by flaring.
construction of the arena took place in 2009 so we chose this year as a
reference. This static LCCF is representative for the year 2009. Any major
change in one of the processes may change the results for other reference
The Life Cycle Impact Assessment (LCIA)
should theoretically be considered over an infinite period of time to take into
account the full
extent of the effects and persistence of these events. In practice, we use models
adapted to the substances analyzed, thus reducing the uncertainties. Since this
analysis focuses on GHGs, the potential effects of emissions can be quantified
for periods of 20, 100 or 500 years. In this study, we use the impact method
"IPCC 2007 GWP 100a  based on . This time period is mandated by
the ISO standard (ISO 14044) and is the most suitable for the lifetime of the
building of 75 years. It is also the time horizon for the global warming
potential of GHG in main international conventions (UNFCCC, Kyoto Protocol,
Western Climate Initiative), as well as in the most recognized carbon footprint
quantification tools such as PAS 2050  and the GHG Protocol for Product
Accounting and Reporting ; other temporal considerations are not itemized .
This section presents
general assumptions regarding the carbon footprint assessment, as well as the
characteristics and parameters of the materials of structures studied.
use phase was not included in this assessment because the structural materials
are not determinative in the choice of materials
used for the building envelope or for insulation. As this is a comparative assessment
and both use phases are equivalent, both are removed from the study. In fact,
this assumption can be considered conservative and favorable to the steel
structure, since the steel framing in the wall reduces the insulating
resistance (R-value), and this is usually compensated by design techniques .
The amount of concrete required for
the construction of foundations does not differ from a steel or a wooden
structure . The amount of concrete for the foundation is more dependent on
the soil and the possibility of earthquakes . Therefore, concrete was not
included in this study as it is the same for the two studies in this comparison.
The lifetime of the arena is
similar, regardless of the structural material chosen. The fatigue resistance
of the two materials in question is most likely exceeding the lifetime of the
building, as discussed in the Forintek report . Biogenic carbon
sequestration is not considered, but is estimated in the discussion section. For
all practical purposes in a dynamic analysis the estimated lifespan of a
non-residential building in North America can be estimated at 75 years .
A few studies mention that deconstruction
is more labor intensive than demolition . The deconstruction phase is not
well documented in North America . Therefore, we took the assumption of the
deconstruction phase to be identical to the construction phase. The model reuses
equipment and cycles times of the construction phase.
The modeling of different machineries
(skidders, cranes, etc.) used in all life cycle processes is not directly integrated into the ecoinvent
database. We therefore resorted to a generic model “diesel burn in building
machine” from ecoinvent.
5. Inventory Data of the
This section provides
an overview of the sources of the data that were used, as well as an analysis
of their quality.
5.1. Data Sources
Primary data were mainly
collected from the producer of glulam beams used in the arena structure. The
collection of these data was carried out during different visits to the
producer with support of those responsible for the various stages of harvesting
and processing as well as accounting data. The construction phase was the
subject of particular attention, with precise monitoring of the assembly and
fuel consumption. Missing, incomplete or not easily accessible data have been
supplemented by the most representative assumptions and secondary data
available in the cited literature or databases (ecoinvent and USLCI). We used
ecoinvent and USLCI databases for different elements of the modeling of the two
compared structures. All the production processes of consumed resources and
waste management, as well as the transport involved in each phase of the life cycle
of both structures were modeled with available secondary data.
5.2. Arena Structures Mass
The components used to model the hybrid structure, the constructed
arena, are detailed
in (Table 1). The building's hybrid structure is composed of a hollow steel
structure, a wide steel section and wood glulam beams assembled by screws, nuts
and bolts that are presented in the mass balance. The components used to model the full steel frame
arena structure are detailed in (Table 2).
In comparison with
the modeling of the current arena, the 111 m3
of wood glulam used for the structure above the ice has been replaced by 114 tons
of steel. The other structural components for the administrative offices, for
the machinery rooms, for the players' rooms and for the internal platforms are the
5.3. Delivery Stage
Fuel consumption was estimated with information
received from suppliers of the two materials studied, distances traveled and
national average fuel consumption by type of truck used. This energy
consumption served as an input into the model and was adapted to represent
North American truck transport. The delivery distance of the steel was modelled
from Toronto (ON) to Chicoutimi (QC) (1 003km) since a large majority of the steel used in the
arena structure comes from the Great Lakes region (personal communication with
Picard Steel, 2011). The transport distance of glulam is real because it is
determined from a known production site in Chibougamau (QC) (358km from
Chicoutimi). Both delivery distances were estimated by using Google Maps.
5.4. Requirements for Data
requirements, according to the ISO standard, must at least ensure their
validity in terms of age, geographical origin and technological performance. Our
study concerns the reference year 2009. The geographical context is an arena in
Quebec. The construction is specific to the Saguenay-Lac-Saint-Jean region, but
some data are aggregated for North America as a whole.
In general, the
available Life-Cycle Inventory (LCI) databases are not representative of
specific reality, as the analysis presented here would require. Data from
ecoinvent, which is the most comprehensive database at present, presents
averages of technology impacts that have not necessarily been updated and that
are mostly derived from the European context. We adapted this databank to the Quebec context for activities
that took place in this province. The ecoinvent data concerning energy supply
have been adapted to Quebec's energy grid (grid mix) to replace the various
European energy sources. This includes, for example, modifying the distribution
percentages of the various countries supplying crude oil resources  and
sources of electricity production in Quebec, which was in 2009, 97% produced by
hydropower . Thus, all the foreground processes, such as industrial process
and transportation, use background processes adapted to the Quebec energy
In addition, the type and consumption of the various
vehicles used have been adapted from the ecoinvent database. For example, a
noticeable difference is observable between the typical European city vehicles
with gasoline modeled in the database and a pickup truck traveling on forest
roads. Therefore, we made some changes, such as the mass of the vehicle and the
fuel consumption to adapt it to the North American context. The vehicle
modeling available in ecoinvent is based on a Volkswagen Golf; the weight is
barely higher than one ton and the consumption is representative of the average
consumption of European vehicles in 2005. We have therefore modified the
quantity of steel in the inventory as well as all emissions by a factor of 2.14
so that it represents a pick-up whose consumption is on average 16.8 l / 100km
(GHG protocol, 2009). In addition, we reduced the impacts to 10 percent
attributable to the manufacture, use and maintenance of road infrastructures,
since these pick-ups would only be running one tenth of the time on paved roads,
according to silviculture workers consulted. Data specific to several other
vehicles, mainly related to forest transport, were also adapted for the
purposes of the study. We have paid particular attention to disaggregate and
document the data collected. (Tables 3) present the approach advocated and are inspired
by Weidema .
Since this study is
limited to the impact of GHG emissions and
their contributions to climate change, we used the "IPCC 2007 GWP 100a"
method for modeling GHG emissions . This method is the result of a
consensus of the most recognized researchers in the field of climate change
with a timeframe of 100 years. The "IPCC 2007" method mainly consists
of characterizing the different GHG emissions contributing to global warming
and then aggregating them into carbon dioxide equivalents (CO2-eq) .
6.1. Application and Limits of the Carbon
Non-residential buildings are most often unique and
complex, making comparisons difficult . It is therefore not recommended to
use the results of this study directly in a context different from this study. The
interpretation of the results
has certain limitations, as demonstrated by the sensitivity analysis in section sensitivity analysis.
Transport is an element that can significantly vary, and may even reverse the
carbon gains from the use of lumber in a building. In addition, the
completeness and validity of the inventory data and the assumptions used also
limit to the conclusions that can be drawn.
6.2. GHG Emissions Results
(Figure 2) presents the GHG emission results of the
two types of structures studied. These results consider carbon emissions for
all the processes described in the inventory for both types of structures over
the entire life cycle. The hybrid structure, steel and wood, totaling 111 m3
of wood glulam, reduced the amount of steel required for the construction of
the arena by 55%, on mass based evaluation. This structure emits 120 tCO2-eq,
while that of steel would have emitted 203 tCO2-eq. So using wood in
the structure reduced the emission of 83 tCO2-eq, or resulted in a 40%
reduction of greenhouse gas emissions.
The first finding is
that steel production has the largest contribution to GHG emissions. It has a
contribution of about 92% in the case of the entirely steel structure. In the
case of the hybrid structure, steel production is also the main contributor with
70% of GHG emissions while it accounts
for only 45% of the mass of materials. The contribution of glulam production is
13%. The second contributor, in order of importance, is associated with the
stages of building and deconstruction in both cases.
In this study, transportation distances are short, so
it is not a hotspot in the life cycle carbon footprint. Nevertheless, glulam
beams are transported on longer distances and mainly by truck, as shown in ,
and therefore this phase may be a bigger contributor than glulam manufacturing
emissions from cradle-to-gate. In these cases, it is advised to use an
alternative mode of transportation that could help to minimize the reduction of
The end-of-life of wood products is probably the phase
where it is easiest to reduce the carbon footprint, even if the impact is low.
Indeed, the use of the wooden material for energy purposes would allow a
possible substitution of fossil fuel, thus reducing the net carbon balance.
6.3. Uncertainty Analysis
Monte Carlo uncertainty analysis was performed in
Simapro software to determine the extent to which a difference between two
scenarios is significant, as explained by . The results of this analysis
are presented in (Figure 2), in which the "l" at the top of the bars
represents the standard deviation on the GHG emissions result.
The USLCI data have the advantage of presenting
processes that are more representative of North American practices. On the other hand, uncertainty is not available
in this source, which removes much relevance to uncertainty analyzes on these
data. With a variability of 2.54%, the uncertainty of the hybrid structure is
higher than the steel structure, which is 0.72%. This difference is explained
by the lack of variability given for the steel production in the USLCI database.
Nevertheless, this lack of precision reinforces the relevance of addressing,
through a sensitivity analysis, the variability of GHG emissions related to
steel production. This analysis is integrated in the following section.
6.4. Sensitivity Analysis
As mentioned above
several parameters used in the model present uncertainties. We have also put
forward several assumptions to make it possible to determine the carbon
footprint of the two types of structures studied. We tested the robustness of those
parameters. The variability of the GHG emissions results demonstrates the
importance of the modified parameters.
6.4.1. GHG Emissions from Steel Production
Initially we used the
USLCI database because it is
representative for North American practices. So for modeling the steel
production we used the inventory name “Iron and steel, production mix/US”. In
order to verify the robustness of this main contributor a sensitivity analysis
was performed on the steel production. We resorted to the reinforcing steel
produced outside of Europe (ROW stands for Rest of the World) of the ecoinvent
database. With the IPCC method, the GHG emission factor is two kgCO2-eq.
/ kg of steel, compared with 0.91 kgCO2-eq. / kg of steel based on the
USLCI data. This notable difference is due to a recycling rate of 56% using the
cut-off rule in the USLCI model, as explained in the documentation . On the
other hand, the recycling of steel is not taken into account in ecoinvent , probably because of a lack of reliable data. The reality is probably
between these two values, which justifies the use of a sensitivity analysis.
(Figure 3) illustrates the results of the sensitivity
analysis on emissions from steel
As shown in the results, GHGs emitted during steel production greatly
influence the carbon footprint of both types of structures. When ecoinvent data
are used to model the hybrid structure, its carbon footprint becomes greater
than the original all-steel structure. However, when compared with the full
steel structure calculated with the ecoinvent data for steel production, the
hybrid structure maintains a significant advantage in terms of GHG emissions. That
result shows how the model for steel production influences the GHG results.
End of Life Scenarios of Wood Glulam
End-of-life scenarios can vary from landfilling to energy valorization. As
we cannot determine the material valuation rate that will be applied when the
arena is demolished, we propose to evaluate the variation between 0 and 100%.
We have assumed that the GHG emissions are a linear function of reduced
landfill, which gives the slope represented in
In contrast with the very conservative scenario "everything to
landfill", the 100% valuation scenario can be qualified as very
optimistic. Indeed, the modeling of an energetic valorization of all the glulam
would be only thermal, since the reduction of the carbon impact for electricity
is not advantageous in terms of substitution in Quebec, because of the already very
low GHG impact of electricity supply in the province. The use for energy
purposes of 111 m3 of wood allows the
substitution of 800 GJ of fossil fuel, or about 30 m3 of natural gas. In addition, we considered that the combustion of wood glulam
is possible directly near the site of the UQAC (hospital complex boiler),
without significant transportation and wood chips are produced with an electric
This valuation provides GHG emission reductions of 2.4 tCO2-eq, a reduction of 1.7% in the balance sheet
of the hybrid structure. This is a low contribution on the final result.
7. Discussion of the
In this section, we will expand the scope of the study. In the first part,
we will try to answer the question: what could be the carbon footprint of a
whole-wood structure? The second part of the section aims to calculate the
potential sequestration of carbon in the structure by integrating biogenic
carbon into the accounting.
7.1. Entirely Wooden
Modern wood construction techniques make it possible to build large
wooden structures. Some arenas, such as the Richmond Olympic Oval (BC) or the
Anaheim ice arena (CA) have a structure with a large proportion of wood. There
does not seem to be any disadvantage from the point of view of the technical
feasibility of proposing a structure entirely made of wood, even if there is
still a need for steel for screws and supports.
It is possible to determine the amount of wood glulam required for a
whole-wood structure, by using the software Athena (Athena Sustainable
Materials Institute, Ottawa, ON). Given the contribution of steel in the hybrid
structure to GHG emissions, it is interesting to conduct the exercise as to
determine the carbon footprint of such a structure.
Modeling the Structure of the Arena Completely in Wood
The components used to model the structure of the arena completely in 100%
glulam are detailed in (Table 4).
In comparison with the current arena hybrid structure, the 83 tons of
steel used for the structure of administrative offices, machinery rooms,
players' rooms and internal platforms were replaced by 76 m3 of glued laminated wood in the
modeling carried out with the Athena software.
Carbon Balance of the Entirely Wooden Structure
In order to add the entirely wooden structure to the carbon footprint comparison
in this study, the same methodology, functional unit and assumptions were used.
(Figure 5) presents the
result of the carbon footprint of the whole-wood structure in comparison with
the two structures studied earlier.
It is easily identifiable that the carbon impact of the structure made entirely
of wood is lower than the two others, with emissions of the order of 58.6 tons
of CO2-eq. So, the wooden structure would have emitted only
half of the GHG emissions from the real (hybrid) structure and one quarter of the total GHG emissions
of the steel structure. The figure shows a distribution of the contribution of
the impacts and results show that the production of glulam greater contribution
to the wood structure GHG impact (37%) than steel production with 22% of the
overall GHG impact. This is due to the low amount of steel needed for this
These results suggest
that maximizing the use of glue-laminated wood in the construction of
non-residential buildings with related structural configurations appears to
have positive effects on the carbon
.2. Biogenic Carbon
Accounting for the biogenic carbon sequestered in harvested wood products is still under discussion [35-37].
From each standard, biogenic carbon must be accounted, but must be separately
presented [38,39]. Since the Quebec forest is sustainably managed and registered
under recognized certification, mainly Forest Stewardship Council (FSC),
Canadian Standards Association (CSA) or Sustainable Forestry Initiative (SFI),
the wood procurement does not result in net deforestation in addition to other
environmental criteria such as biodiversity, aquatic effects and soil impact .
Obviously, wood contains carbon, because each carbon atom in the wood is
derived from an atmospheric CO2 molecule
captured by photosynthesis. It is generally accepted that wood is composed of
50% biogenic carbon by dry mass in average . Based on of the
Quebec’s glulam LCA study, the density is 520 kg/m3 and contains
22.5 kg of residual glue. That corresponds to 249 kg of carbon, or 914 kg CO2
per m3 of glulam. By subtracting the 102 kg emitted throughout the
entire manufacturing cycle, a cubic meter of Quebec’s wood glulam sequesters a
net 812 kg of CO2 .
According to these
estimates, (Figure 6) presents the integration of biogenic carbon in the LCCF
results. This calculation makes the wood structure even more advantageous by doubling the
difference between the hybrid and steel structure total carbon emissions. By
sequestering more carbon than anthropogenic emissions in the whole-wood
structure, it could be carbon negative. In terms of mitigation of climate change
this makes the use of wood even more interesting than other types of materials
as carbon negative measures are requested to fulfill the goal of the Paris
Accord to keep climate warming “well under 2 degrees before 2100”. It should be
noted that when the material is decomposed after use, e.g. by energy
valorization, the sequestered carbon is released again. However, when all such
structures would be wood-only, it could significantly contribute to carbon
sequestration over time periods of 75 years.
This study aimed to quantitatively determine the life cycle carbon
footprint of the hybrid structure of the Université du Québec à Chicoutimi arena
and to compare it to that of an entirely steel-made structure modelled for the
same building. Based on the nature of the specific data used for a building
constructed in 2009, but expected to remain functional for a few decades. As
such, this comparative assessment will remain relevant for a long time, as
building materials technology, such as glulam, is still under development in
the non-residential construction sector in North America. The results of this
case study show a net reduction in GHG
emissions by using wood materials in the structure of a non-residential
building. The construction of the hybrid structure has saved 83 tons of CO2-eq,
or 173 tCO2-eq when the positive effect of biogenic carbon
sequestration is taken into account.
Given the result of the
comparison with the entirely wooden structure, the University could have reduced
the impact of climate change by an additional 61 tCO2-eq (and 122
tCO2-eq, including biogenic carbon) by using more wood in its arena
Although the wood material has already been documented as a lower emitter
than steel over the entire life cycle, within the context of Quebec it is
particularly favorable as non-residential building material. The availability
of raw materials and their renewable nature are fundamental elements, and the
low carbon intensity of electricity in the Quebec network contributes to
consolidating these advantages. Indeed, much of the energy consumed by the
forest industry is electrical, especially for sawing. The general conclusions
were drawn from a site-specific study. However, this study can reinforce the
interest for non-residential wood buildings in the light of greenhouse gas emission
reduction, especially when wood procurement can be certified for sustainable
management of forests.
Finally, regarding the displacement factor mentioned in the
introduction, the indices calculated from the results of this case study are
between 0.83 tC/tC for the hybrid structure and 1.76 tC/tC for the structure
entirely made from wood, including biogenic carbon sequestration accounting.
The displacement factors in this study are therefore below the average of 2.1
tC/tC calculated by Sarthe & O'Connor (2010) and this demonstrates the need
for precise carbon footprint accounting to achieve GHG reductions with wooden
Figure 1: System boundaries of the study
Figure 2: Comparative
Greenhouse gas emissions of the hybrid and the steel structure.
Figure 3: Steel production sensitivity
Figure 4: Sensitivity
analysis of wood glulam end of life scenarios.
Figure 5: Wood structure carbon footprint
Figure 6: Biogenic carbon integration.
Hollow structural steel
Wide flange section
Screws, nuts & bolts
Table 1: Hybrid structure mass balance.
Wide flange section
Screws, nuts & bolts
Table 2: Steel structure mass balance.
Life cycle stages
Further technological correlation
End of life
Table 3: Data quality matrix.
Hollow structural steel
Screws, nuts & bolts
Table 4: Wood structure mass balance.
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Citation: Laurent AB, van der Meer Y and Villeneuve C (2018) Comparative Life Cycle Carbon Footprint of a Non-Residential Steel and Wooden Building Structures. Curr Trends Forest Res: CTFR-128. DOI: 10.29011/ 2638-0013. 100028