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Life cycle analysis of cross laminated timber in buildings: a review

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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.
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Life cycle analysis of cross laminated timber in
buildings: a review
Xavier Cadorel
The University of Melbourne, Melbourne, Australia
xavier.cadorel@unimelb.edu.au
Robert Crawford
The University of Melbourne, Melbourne, Australia
rhcr@unimelb.edu.au
Abstract: 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.
Keywords: Cross laminated timber; life cycle assessment; greenhouse gas emissions; construction.
1. INTRODUCTION
The latest quarterly update of the National Greenhouse Gas Inventory December 2017 reveals that Australian GHG
emissions have increased by 1.5 percent compared to the previous year (Department of the Environment and Energy, 2018).
Unfortunately, this increase in national GHG emissions has been consistent for the last three years, thus making it more
difficult to achieve the 2030 target of reducing GHG emissions by 26-28 per cent from 2005 levels (Australian Government,
2015). Moreover, this 2030 target is conservative and will result in Australia emitting about 85% of its IPCC Carbon Budget
in only 14 years. Accordingly, there will potentially remain only 15% of this budget for the following twenty years, until 2050,
at which stage, the national population is projected to reach between 33 and 40 million (Krockenberger, 2015). It is therefore
reasonable to express concerns regarding the ability for Australia to successfully meet the Paris Agreement, and it highlights
the current emergency for the nation to rapidly reduce GHG emissions.
1.1 Carbon footprint of buildings
According to the Intergovernmental Panel on Climate Change (IPCC), buildings (residential and commercial) accounted for
19% of energy-related global GHG emissions in 2010 (IPCC, 2014). More recent studies estimate the global GHG emissions
contribution from buildings at between 30-40% (Ibn-Mohammed et al., 2013; GABC, 2017; Sandanayake et al., 2018).
Recent studies, using life cycle assessment (LCA), have identified the source of those large GHG emissions and revealed
that indirect emissions, in comparison to direct emissions occurring during the use stage of buildings, are responsible for a
major and increasing proportion of the total GHG emissions. This share is found to range from 71% in Ireland (Acquaye and
Duffy, 2010), to 89.5% in Australia (Yu et al., 2017), and even up to 96.6% in China (Chen et al., 2017).
Referring to the European Standard EN15978 (2011), Figure 1 shows that the building life cycle includes four distinct
stages from which GHG emissions result. The use stage (B), relates to the time in which the building is occupied, and its
operation produces direct GHG emissions from the energy it uses. In addition, indirect GHG emissions are produced by
Stages A, C and D, relating to the ‘product’ and ‘construction’ stage, the ‘End of Life (EOL)’ stage and the ‘Benefits and
loads beyond the system boundary’ stage, respectively.
P. Rajagopalan and M.M Andamon (eds.), Engaging Architectural Science: Meeting the Challenges of Higher Density: 52nd
International Conference of the Architectural Science Association 2018, pp.107–114. ©2018, The Architectural Science
Association and RMIT University, Australia.
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Figure 1: Life cycle stages. Source: adapted from EN 15978:2011 (2011)
For decades, construction regulations relating to the reduction of GHG emissions have focused on the building use
stage and have largely disregarded potential GHG emission reductions in the three others stages, in particular Stage A.
Indeed, the product and construction process stage not only represents a significant share of the indirect GHG emissions
(Crawford and Stephan, 2013), it is also a stage where decisions regarding materials and construction processes can be
most easily changed for better long-term GHG emissions outcomes. Thus, an increasing number of studies have promoted
a more holistic approach to GHG emissions reduction, using LCA inter alia (Hafner, Winter, and Takano 2012; Crawford et
al. 2016).
1.2 GHG emissions of conventional structural materials
The construction of conventional buildings in most parts of the world uses highly emissions intensive materials, such as
concrete and steel for their main structural elements. In 2014, it was estimated that energy-related GHG emissions from
iron, steel and cement manufacturing represented 9% of global GHG emissions (GABC, 2017). Concrete has benefited
from considerable research aiming to reduce GHG emissions, particularly those related to producing Portland cement
(Schneider et al., 2011; Gartner and Sui, 2017). Yet, it is estimated that by 2050 the global GHG emissions share associated
with Portland cement will represent 26% if current manufacturing processes remain unchanged, or still 20% even if cutting-
edge processes are implemented (Gunner, 2017).
Steel production has seen similar progress regards to GHG emissions reduction, through replacement of formulas (Van
Wesenbeeck et al., 2016), or innovative processes, such as molten oxide electrolysis (Allanore et al., 2013). Yet severe
technology hurdles have cut short implementation in industry, and iron and steel production are currently estimated to
account for 6.7% of global GHG emissions. This is anticipated to rise if disruptive innovations and international collaboration
aren’t implemented (Shatokha, 2016). Therefore, the global GHG emissions share associated with concrete and steel is
projected to remain significant and a substantial barrier to achieving necessary GHG emissions reduction targets within
the building industry. Furthermore, most conventional materials, including the two mentioned above are of mineral and
non-renewable nature. When considering that the Australian building stock is predicted to double by 2050 (ASBEC, 2017),
severe stress on raw mineral resources is highly likely.
1.3 Cross-laminated timber: an alternative structural material
In London, a breakthrough occurred when Waugh Thistleton Architects designed the Stadthaus, a nine storey tower in North
London, UK (Thompson, 2009), using Cross Laminated Timber (CLT). CLT is an Engineered Wood Product (EWP) panel
composed of layers of solid timber called lamellas, typically 12 to 45 mm thick and 40 to 300 mm wide, glued together. The
novelty of CLT comes from the 90° orientation of each layer of lamellas to adjacent layers, thus achieving better structural
rigidity and dimensional stability in both direction of the panel. CLT panels are typically 57 to 320 mm thick, ranging from 2.2
to 2.95 m wide and up to 11.9 m long depending on transport constraints (England and Iskra, 2016).
CLT is a bio-sourced, and thus renewable material. Therefore, it could potentially mitigate the risk of raw mineral resource
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depletion related to the use of conventional structural materials, such as steel and concrete. Besides other advantages
such as safety and construction time savings, previous studies have also demonstrated other potential environmental
benefits. An Australian study published by Durlinger et al. (2013) with a case study of Melbourne’s Forté building, commonly
accepted as the most significant CLT construction in Australia, confirmed these benefits with a Global Warming Potential
(GWP) 13%-22% lower than a building of similar design using concrete.
Durlinger et al.’s study is one of several studies that have used LCA to assess the environmental performance of CLT
construction and compare it with conventional construction, most often Reinforced Concrete (RC) construction. These
studies vary widely in the LCA methodologies used and their complexity, but all try to answer the same question: What is
the potential for CLT construction to reduce the GHG emissions associated with buildings?
2. CRITICAL REVIEW OF PREVIOUS STUDIES
While CLT brings clear benefits over steel and concrete in terms of minimising non-renewable material depletion, the extent
of other environmental benefits is less certain. This certainty is needed to ensure it provides a viable solution to mitigate
environmental issues, such as the release of GHG emissions, associated with the built environment. A critical review was
conducted on selected previous international LCA studies comparing conventional and CLT construction.
2.1 Methodology
The review of LCAs of CLT construction was based on the systematic approach used by Booth et al., including two stages:
scoping review and mapping review. First, the scoping review was used to assess the number and quality of publications
on the relevant topic and reveal primary gaps within the literature. Secondly, the mapping review maps existing literature
and identifies secondary gaps, which leads to a summary assessment and identification of areas for future research (Booth
et al., 2016).
The search process included three main steps. First, an initial search using keywords, as listed in Table 1, in Google
Scholar, Scopus and Web of Science databases. The first one hundred results from each search from each database
were considered, resulting in an initial batch of nine international articles (including P1-3, P5-8, as per Table 2). Secondly,
further research through Google Scholar alerts and the ResearchGate community resulted in four more relevant publications
(including P4 and P9). Finally, meetings and discussions during conferences resulted in one more research report. Therefore,
a total of 14 relevant studies were identified for further analysis.
Table 1: Keywords used for searching for LCA studies of CLT.
Comparative cross laminated
timber life cycle assessment
Comparative CLT LCA
buildings
Life cycle approach cross
laminated timber CLT
Environmental impacts cross
laminated timber CLT
GWP climate change mitigation
MTC mass timber construction
Cross laminated timber CLT
zero energy
Cross laminates timber CLT
passive house
Cross laminated timber CLT
positive low energy building
2.2 Selection of studies for review
To guarantee the quality of this review, only peer reviewed studies were selected. This process removed two studies from
the review selection, a Masters thesis from Canada and one industry report from Australia. As this study focusses on the use
of CLT in the building context, only studies that considered entire buildings were analysed in further detail. This, excluded a
US study from the review. Furthermore, the quality and consistency of this review is maintained by further limiting the scope
to CLT construction and so excluding an Australian study that focuses on Laminated Veneer Lumber. A final study from
Germany that treats about a single dwelling house has also been excluded as it represents a unique case compared to all
other studies that assess multi-storey buildings ranging from 4 to 21 levels. The nine remaining studies have been reviewed,
as detailed in Table 2.
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Table 2: Nine published LCA studies of CLT construction selected for review.
Publication Author(s) (Year) Title Country
P1 Robertson et al.(2012) A Comparative Cradle-to-Gate Life Cycle Assessment of Mid-
Rise Office
Canada
P2 Darby et al. (2013) A Case Study to Investigate the Life Cycle Carbon Emissions
and Carbon Storage Capacity of a Cross Laminated Timber,
Multi-Storey Residential Building
United Kingdom
P3 Durlinger et al.(2013) Life Cycle Assessment of a Cross Laminated Timber Building Australia
P4 Grann(2013) A Comparative Life Cycle Assessment of Two Multi-Story
Residential
Canada
P5 Dodoo et al. (2014) Lifecycle Carbon Implications of Conventional and Low-Energy
Multi-Story Timber Building Systems.
Sweden
P6 Skullestad et al.(2016) High-Rise timber Buildings as Climate Change Mitigation
Measure - A Comparative LCA of Structural System
Alternatives
Norway
P7 Guo et al.(2017) A Comparison of the Energy Saving and Carbon Reduction
Performance between Reinforced Concrete and Cross-
Laminated Timber Structures in Residential Buildings in the
Severe Cold Region of China
China
P8 Rajagopalan and Kelley(2017) Evaluating Sustainability of Buildings Using Multi-Attribute
Decision Tools
United States of
America
P9 Teh et al.(2017) Replacement Scenarios for Construction Materials Based on
Economy-Wide Hybrid LCA
Australia
3. LITERATURE REVIEW
Results of all previous studies, except for some scenarios of P2 and P9, show Global Warming Potential (GWP) benefits
for CLT construction compared to conventional construction. However, a comparison of final results regarding GWP from
these nine papers is extremely difficult. Indeed, the difference in GWP benefits of CLT ranges from +15%, meaning that
CLT buildings result in more GHG emissions than RC ones, to -278%. This broad variation is a result of variations in
study parameters such as local climate, building legislation, energy mix, but also assessment methods including system
boundaries, carbon estimation, data quality and overall LCA approach.
3.1 Building characteristics
The wide range of buildings assessed, as shown in Table 3, is one source of variation in the results of the various studies.
Two major variables are observed, first the presence or not of a RC basement that reduces the potential GWP reduction of
CLT buildings that can be achieved through reduced footings. Second, the number of levels also increases the RC share in
a CLT building, since footings are dimensioned according to building height and stress load. For example, hybrid structural
systems with concrete cores are often used for taller CLT buildings. Table 3 shows the mix of structural materials (CLT, RC
and steel) assumed for buildings modelled in each study.
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Table 3: Building details, uses and construction status of the nine published studies selected for review.
Building details Use Status
P1 1 CLT vs. 1 RC, 5 levels, RC basement 100% Commercial RC built
CLT hypothetical
P2 1 CLT vs. 1 RC, 5 & 8 levels, no basement 100% Residential CLT built
RC hypothetical
P3 1 CLT vs. 1 RC, 10 levels, no basement 89% Residential and 11%
Commercial
Both built
P4 1 CLT vs. 1 RC, 4 levels, RC basement 100% Residential CLT built
RC hypothetical
P5 1 CLT vs. 1 Timber post & beam vs. 1 Timber modular, 4 levels, no
basement
100% Residential All hypothetical
P6 4 CLT vs. 4 RC, 3, 7 ,12 & 21 levels, RC basement 100% Residential All hypothetical
P7 4 CLT vs. 4 RC, 4,7,11 & 17 levels, No basement 100% Residential RC built
CLT hypothetical
P8 1 CLT vs. 1 RC vs. 1 Steel frame, 9 levels, No basement 50% Residential and 50%
Commercial
All hypothetical
P9 New building stock replaced by CLT, 10 levels, No basement 100% Residential and 100%
Commercial
All hypothetical
3.2 Regional variation
When analysing CLT buildings from the most comparable papers P2, P3 and P7, since they are mostly residential, without
a basement and of similar height, one can observe that their results regarding total GHG emissions fluctuate from 0.16
tCO2e/m2 to 5.98 tCO2e/m2. This large variation can be explained first by the difference of climate. Operational energy (OE)
demand to reach comfort in severe cold Harbin, China (P7), far exceeds that in the more temperate London, UK (P2). In
addition, variation of building codes and thermal stringencies potentially escalates this variation. For example, for an external
CLT wall in a cold climate (P5), under Swedish conventional design a minimum of 245mm of rock wool, estimated at R5.4,
is required. In comparison, under a Chinese improved design (P7), the building requires only 50 mm of EPS, estimated at
R1.78.
Finally, the energy mix for each of the locations also plays a significant role in the resultant GHG emissions. While the CLT
building in P3 located in Melbourne, Australia, should benefit from a milder climate than in P2 (UK), the carbon intensity of
the Victorian energy mix, mostly generated from brown coal, dramatically increases GHG emissions compared to London
where coal represents less than 40% of the total energy mix, with hydro and wind representing more than 20% (Department
of Energy and Climate Change, 2013). When comparing results from international studies, these regional variations are
critical to consider, and furthermore, they will evolve as construction standards change, the energy mix becomes cleaner,
and climate changes.
3.3 System boundary
One of the main reasons for the variation in the GHG emissions of CLT construction amongst the nine selected studies is the
system boundary considered. LCA enables a holistic approach when studying the life cycle of a product, however for many
studies a streamlined approach is used, excluding many life cycle stages. Table 4 shows that only four studies out of nine
consider the full life cycle of the buildings, from ‘cradle to grave’. While a cradle to gate system boundary can be justified
to detect carbon ‘hotspots’ at Stage A (Figure 1), the major drawback is that this can potentially lead to conclusions about
the GWP benefits that can be counterbalanced in later stages of the building’s life. For example, study P3 shows that CLT
construction has 30% lower GWP than RC construction at Stage A (cradle to gate). However, when considering Stages A
to D (full life cycle) and EOL scenario without carbon sequestration, CLT is shown to have a GWP 15% higher than RC. This
is concerning given that this information can be used to inform material choices. It is therefore critical to analyse the full life
cycle implications of the use of CLT in buildings to be able to more reliably draw conclusions on the net GWP benefits of
CLT construction.
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Table 4: System boundary and lifetime horizon for the nine published studies selected for review.
System boundary
Publication Lifetime horizon and
comments
Publication Lifetime horizon and
comments
Publication Lifetime horizon and
comments
P1 50 years, Stage A5
excluded
P2 50 years, Stage B
excluded
P3 50 years
P6 60 years, Stages A4 &
A5 excluded
P4 60 years
P9 Not applicable, Full
Stages A1 to A5 included
P5 50 years
P7 50 years
Note: Publication P8 doesn’t mention system boundary and lifetime horizon.
3.4 Assessment of carbon cycle
Amongst the nine studies reviewed, there is a clear division regarding the method used in assessing life cycle GHG emissions.
Five studies out of nine consider a percentage, ranging from 0% to 100%, for carbon sequestration. Carbon sequestration
is the process performed by trees in removing atmospheric CO2 and storing it as carbon in wood fibres. This carbon, called
biogenic carbon, is removed from the atmosphere as long as the wood product is used. According the EOL scenario, all
biogenic carbon is either returned to the atmosphere (0% sequestration), and this is the case for bioenergy, or is reused in
another wood product (100% sequestration) for the life of the secondary wood product. Depending on the percentage of
sequestration, GHG benefits fluctuate largely and have led to confusion on the GHG emissions balance of CLT construction.
Three other studies, did a full assessment of the life cycle of biogenic carbon, two of them followed the IPCC
recommendations in considering biogenic carbon as neutral GWP. Alternatively, Grann (2013) (P4), hasn’t followed the
IPCC recommendations and has included the change of forest albedo at harvest site, as well as considering concrete
carbonation in their RC scenario. This study also explores various EOL scenarios, including landfill, bioenergy and reusing or
recycling, resulting in a thorough assessment of the biogenic carbon life cycle, which differs from most of the other studies.
Compared with a sequestration percentage, which can be confusing information for decision makers, Grann’s approach in
assessing the full biogenic carbon life cycle results in more accurate, detailed and valuable outcomes regarding the GWP
benefits of CLT construction.
3.5 LCA method and data
Out of the nine selected studies, eight studies apply an LCA approach and one, P8, uses a survey approach with its
conclusion limited to identifying potential ‘hot spots’ associated with CLT construction. Seven studies out of the eight that
use LCA, used a process-based approach, which is often considered acceptable for comparative studies, but ill equipped
to provide a comprehensive estimation of GHG emissions associated with CLT construction.
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Harvey (2012) stated that ‘to rely entirely on a process-based approach will underestimate the true embodied energy
and subsequent environmental burdens, since interactions beyond some relatively low order [processes] will be omitted
(that is, there is a truncation error)’. This finding has also been reinforced by Lenzen and Treloar (2002) who estimated,
in a comparative study of a wood frame versus RC building, that a process-based approach underestimated the GHG
emissions by a factor of two, compared with an economy-wide input-output (IO) approach.
This IO method has been further developed into hybrid methods that integrate both the precision of the
process-based method and the comprehensiveness of the IO method, and this is the method used by Teh et
al. (2017) (P9). Unfortunately, due to the limitation of this study’s scope, the system boundary has been restricted to
cradle to gate and so missed the opportunity to reveal a broader economy-wide estimation of the GHG emissions from CLT
buildings.
The quality and relevance of data regarding CLT products has been an ongoing challenge evidenced by these nine
studies. Since CLT is a relatively new construction material, with only a limited, but growing, number of manufacturers,
data regarding its environmental performance is rare, which has resulted in approximations or considerable limitations in
assessment of its environmental performance.
4. CONCLUSION
This paper has provided a review of studies on the environmental performance of CLT building construction. The review
of nine studies reveals that most conclude that CLT construction results in lower GHG emissions than conventional RC
construction. However, there is a wide range of results due to the variety of buildings assessed, regional variations, the
treatment of biogenic carbon, LCA approach used, and data source. Only one study uses a comprehensive hybrid LCA
approach, but even this study suffers from limitations, i.e. a limited scope. This study has highlighted the need for further in-
depth analysis of the environmental performance of CLT construction using a hybrid LCA approach, complimented with CLT
production process data, comprehensive consideration of concrete carbonation and biogenic carbon. This would provide
a more realistic estimation of the potential for CLT construction to reduce GHG emissions associated with buildings. The
new knowledge generated would form an important element of the decision-making process for the selection of structural
materials, potentially integrated with the framework for assessing the environmental benefits of mass timber construction
proposed by Crawford and Cadorel (2017).
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180 211–220.
X. Cadorel and R. Crawford
... El uso creciente de nuevas tecnologías de construcción en altura con madera masiva (compuestos de madera laminada [ML] y contralaminada [MCL]) representa un potencial poco explorado para contribuir a mitigar los efectos nocivos de la edificación (Ramage et al. 2017). Resultados de análisis de ciclo de vida (ACV), donde se trazan emisiones GEI/GCA para todas las etapas de la edificación (ISO 2006), destacan las ventajas de la madera masiva comparada con sistemas tradicionales de hormigón y tabiquería liviana para habilitar edificios de cero emisiones de carbono (CEC) edificios cuyos balances netos de emisiones de ciclo de vida o ciclo anual son negativos o iguales a cero (Cadorel & Crawford 2019). Estas ventajas incluyen la capacidad de la madera masiva de secuestrar grandes cantidades de carbono (Heräjärvi 2019); disminuir entre 40-60% las emisiones de manufactura y construcción (Morales Vera et al. 2020); reducir demandas de combustible de climatización entre 60-90% (Felmer & Yannas 2018); y facilitar su reutilización posterior para nuevas edificaciones (Nakano et al. 2020). ...
Research Proposal
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Este proyecto tiene como propósito el diseño de soluciones constructivas que permitan mejorar él comportamiento térmico de envolventes de madera masiva y evaluar sus efectos sobre el confort térmico interior en habitáculos de prueba que serán instalados en el centro tecnológico para la construcción (CTeC), ubicado en Santiago (33oS). Los estudios se centran en el desarrollo y aplicación de técnicas avanzadas de climatización pasiva aprovechando la capacidad de envolventes de madera masiva (principalmente Madera Contralamina-da [MCL]) de generar inercia ante la amplitud térmica diaria presente en localidades de climas mediterráneos. Esta propiedad, que contribuye a moderar el flujo diario de energía solar pasiva, es instrumental para reducir la alta dependencia de combustibles que afecta a viviendas del centro y sur del valle central de Chile donde más de la mitad de la energía auxiliar se consume en calefacción ─aproximadamente 100 kWh/m 2 año por vivienda. Si bien existe consenso internacional de que la construcción con madera masiva permite secuestrar grandes cantidades de carbono (-1.0 tonCO2/m 3) su comportamiento térmico es un tema aun poco estudiado en la literatura especializada, cuyo avance, no sólo será un aporte importante para el conocimiento, sino que traerá consigo inmensas consecuencias económicas y sociales para el país. El objetivo del proyecto es formular soluciones de envolvente en base a paneles prefabricados de MCL modular compuestos con biomateriales renovables de alta capacidad térmica que permitan crear condiciones estables de temperatura interior para el uso efectivo de componentes operables de control pasivo, sin recurrir al uso de energía auxiliar (como ventanas, celosías, cortinas o persianas). Para ello, la metodología propuesta consiste en una serie de estudios analíticos combinados con mediciones empíricas que se llevarán a cabo en el parque de innovación de CTeC, ubicado en Laguna Carén. Estos comprenderán, en una primera etapa, la modelación de un edificio piloto de viviendas de MCL en altura para establecer la influencia relativa de sus componentes sobre sus emisiones de carbono; en una segunda etapa, el monitoreo del comportamiento térmico de un módulo de departamento del edificio construido en el parque, denominado Prototipo-CERO, con el fin de calibrar su simulacion térmica computacional; en una tercera etapa, ensayos de laboratorio para la caracterización termofísica de paneles de MCL de pino-radiata nacional con otros materiales de interés que informarán el diseño de nuevas soluciones; y por último, en una cuarta etapa, junto con ensayos de verificación en celdas de prueba en CTeC, análisis extensivos de simulación para evaluar el potencial de climatización pasiva de las soluciones propuestas para la vivienda prototipo en Temuco (38oS) y Puerto Montt (41oS). La contribución científica de esta investigación consiste en cubrir el vacío de conocimientos existentes en la literatura internacional sobre el acondicionamiento térmico de viviendas de madera masiva, comprender sus propiedades de comportamiento térmico dinámico y las nuevas posibilidades que ofrece para la climatización natural. En países en vías de desarrollo como Chile, que se encuentra entre los diez mayores exportadores de madera del mundo, la construcción de viviendas de madera masiva podría ser instrumental para la descarbonización sistemática del sector de la edificación. Se espera que los resultados permitan demostrar la contribución de las soluciones propuestas para la construcción de viviendas de cero emisiones de carbono que alcancen consumos de combustible de climatización cercanos a cero o inferiores a 5.0 kWh/m2 año (<0.003 tonCO2/m2 año) para gran parte del territorio continental del país. Se espera además por medio de índices que serán presentados para el desarrollo de la investigación que la aplicación extensiva de las soluciones propuestas para la construcción de nuevas viviendas, puedan aportar a mejorar sustantivamente condiciones de confort térmico interior, reducir gastos energéticos del hogar y emisiones de gases contaminantes atmosféricos asociados al uso de artefactos de climatización intradomiciliaria.
... There have been research projects in Europe that points towards replacing concrete with cross laminated timber (CLT) in critical support structures in buildings [3,4]. This will not only reduce the greenhouse gas emission, that are made when manufacturing cement, but also make the building a carbon sink [5,6]. CLT consists of multi-layered wood planks where the layers are organised crosswise and connected by adhesive bonding [4]. ...
Article
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The theory and applications of Smart Factories and Industry 4.0 are increasing the entry into the industry. It is common in industry to start converting exclusive parts, of their production, into this new paradigm rather than converting whole production lines all at once. In Europe and Sweden, recent political decisions are taken to reach the target of greenhouse gas emission reduction. One possible solution is to replace concrete in buildings with Cross Laminated Timber. In the last years, equipment and software that have been custom made for a certain task, are now cheaper and can be adapted to fit more processes than earlier possible. This in combination, with lessons learned from the automotive industry, makes it possible to take the necessary steps and start redesigning and building tomorrows automated and flexible production systems in the wood industry. This paper presents a proof of concept of an automated inspection system, for wood surfaces, where concepts found in Industry 4.0, such as industrial Internet of things (IIoT), smart factory, flexible automation, artificial intelligence (AI), and cyber physical systems, are utilized. The inspection system encompasses, among other things, of the shelf software and hardware, open source software, and standardized, modular, and mobile process modules. The design of the system is conducted with future expansion in mind, where new parts and functions can be added as well as removed.
... A few comprehensive studies have been reported on the life cycle climate impacts of CLT buildings. In a recent review of life cycle analyses of CLT in buildings, Cadorel and Crawford (2018) identified only nine detailed studies in the literature and most of these focused on the cradle-to-gate stages, with simplified modelling of the impact of the endof-life stage. For example, Balasbaneh and Sher (2021) evaluated the life cycle environmental implications of hypothetical single-family building designed, using CLT or glue-laminated timber structural elements. ...
Article
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Low-carbon buildings and construction products can play a key role in creating a low-carbon society. Cross-laminated timber (CLT) is proposed as a prime example of innovative building products, revolutionising the use of timber in multi-storey construction. Therefore, an understanding of the synergy between structural engineering design solutions and climate impact of CLT is essential. In this study, the carbon footprint of a CLT multi-storey building is analysed in a life cycle perspective and strategies to optimise this are explored through a synergy approach, which integrates knowledge from optimised CLT utilisation, connections in CLT assemblies, risk management in building service-life and life cycle analysis. The study is based on emerging results in a multi-disciplinary research project to improve the competitiveness of CLT-based building systems through optimised structural engineering design and reduced climate impact. The impacts associated with material production, construction, service-life and end-of-life stages are analysed using a process-based life cycle analysis approach. The consequences of CLT panels and connection configurations are explored in the production and construction stages, the implications of plausible replacement scenarios are analysed during the service-life stage, and in the end-of-life stage the impacts of connection configuration for post-use material recovery and carbon footprint are analysed. The analyses show that a reduction of up to 43% in the life cycle carbon footprint can be achieved when employing the synergy approach. This study demonstrates the significance of the synergy between structural engineering design solutions and carbon footprint in CLT buildings.
... They showed that timber has less impact compared to other materials. Cadorel et al. [22] reviewed building materials and suggested that using CLT could reduce greenhouse gas (GHG) emissions from the construction sector [23]. assessed the LCA and embodied energy of CLT building structures from the cradle to the grave, showing that the GWP impact was very low due to the CO 2 sequestration of wooden materials [24]. ...
Article
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The environmental emissions and energy from construction activity and building materials contributes significantly to a building's sustainability. Previous research dealing with wood or engineering wood's energy requirements compared to reinforced concrete and steel structures has shown that embodied energy and embodied carbon is significantly lower in wood-based construction. This study has assessed the environmental impact and costs of glued laminated timber (GLT) or cross-laminated timber (CLT). Hardwood and softwood variants of both GLT and CLT were considered. We compared the life cycle costs (LCC) of these alternatives to discover the lowest cost. The comparative results indicated that GLT has higher emissions in Global warming potential (GWP), Terrestrial Ecotoxicity (TE), Land Use (LUP), and Ozone layer depletion (OLD), while CLT has higher impact in Human-Toxicity Potential (HTP), Fossil Depletion Potential (FDP). The results indicated that using CLT significantly reduces embodied energy by 40%. However, a comparison of costs showed that CLT is 7% more expensive than GLT. Establishing which material performs best based on environmental and economic criteria thus required further analysis. Thus, the multi-criteria decision making (MCDM) method was applied. This showed that CLT manufactured with softwood is the most sustainable choice among the alternatives considered. This study's findings are important for aggregate level decision making of different wood materials for residential buildings.
... Numerous studies have investigated the environmental benefits of CLT construction in comparison to conventional construction, typically using a life cycle assessment (LCA). Yet, Cadorel and Crawford (2018) have highlighted the need for further in-depth analysis of the environmental performance of CLT construction using a more comprehensive approach for quantifying the production-related (or embodied) loadings of CLT, namely the Path Exchange (PXC) hybrid approach. The PXC approach is a hybrid approach for quantifying embodied loadings that integrates the precision of a process analysis and the comprehensiveness of environmentally-extended input-output (EEIO) analysis (Crawford et al., 2017). ...
Conference Paper
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Numerous studies have investigated the environmental benefits of cross laminated timber (CLT) construction in comparison to conventional construction, typically using a life cycle assessment (LCA). Yet, there is a need for further in-depth analysis of the environmental performance of CLT construction using a more comprehensive approach, in order to provide a more realistic estimation of the potential for CLT construction to reduce greenhouse gas (GHG) emissions associated with buildings. This research aims to fill this knowledge gap by conducting a streamlined life cycle assessment to quantify embodied GHG emissions, using hybrid coefficients from the EPiC Database, for a real case study; a five storey multi- residential CLT building about to be constructed in Melbourne, Australia. The new knowledge will provide some of the critical knowledge that is currently lacking in relation to the life cycle GHG emissions performance of CLT construction and the potential for this form of construction to reduce GHG emissions associated with the construction industry. (2) (PDF) Greenhouse gas emissions performance of cross laminated timber construction using hybrid life cycle assessment. Available from: https://www.researchgate.net/publication/350890919_Greenhouse_gas_emissions_performance_of_cross_laminated_timber_construction_using_hybrid_life_cycle_assessment [accessed Apr 16 2021].
... The local sourcing of lumber and the use of lighter species instead of heavier species were pointed out as factors that could significantly reduce the global warming potential of CLT products. Cadorel and Crawford [10] presented a review of studies related to the environmental performance of CLT buildings. The authors referred that most of the analysed studies concluded that CLT buildings have lower greenhouse gas emissions than RC solutions. ...
Article
A sandwich wall-panel solution based on Cross-Laminated Timber (CLT) has been recently developed aiming to rationalize the wood volume and combine it with a low-density core layer for improved thermal insulation and reduced weight. Such panel, named Cross-Insulated Timber (CIT), was previously optimized to fulfil structural and thermal requirements with a minimum production cost. The layout of the new panel is similar to the one of a five-layer CLT panel, but the inner layer is made of polyurethane rigid foam instead of timber. Besides its technical and economical benefit, it is also of interest to assess its environmental impact. This paper presents a study about the environmental impact assessment through Life-Cycle Analysis (LCA) of this new type of wood-based sandwich wall panel. A cradle-to-gate LCA with consideration of different end-of-life scenarios is performed in order to identify the processes that contribute the most to the environmental impact of the CIT panel solution proposed during its life cycle, namely during manufacturing. The LCA includes also the comparative assessment of: (i) varying the thickness of the wood layers, with respect to the optimized CIT panel; (ii) using an alternative core material, namely insulation cork board (ICB), and (iii) applying structurally equivalent three-layered CLT solutions, with alternative core materials. The results obtained show that the manufacturing process of the CIT panel, namely the polyurethane foam production and the press and curing processes during the panels assembly are the ones that produce the highest impacts. It was also found out that varying the thickness of the wood layers compared to the optimized solution leads, in general, to an increase in all impact categories. This means that the optimized solution in terms of economic costs is also the one which presents the lowest environmental impacts. Compared to equivalent CIT panels with ICB core and CLT solutions, the environmental performance of the panel proposed was better for some impact categories, while it was worse in others.
... These results are consistent with Cadorel and Crawford's (2018) review of CLT LCAs which found substituting wood for conventional building materials results in reduces greenhouse gas emissions. In a review of global emissions from the construction sector, Huang et al. (2018) also conclude that substituting conventional building materials for those with low embodied carbon, like wood, is a key strategy to reducing global greenhouse gas emissions. ...
Article
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We conducted a systematic literature search and meta-analysis of studies with side-by-side life cycle analysis comparisons of mid-rise buildings using mass timber and conventional, concrete and steel, building materials. Based on 18 comparisons across four continents, we found that substituting conventional building materials for mass timber reduces construction phase emissions by 69%, an average reduction of 216 kgCO2e/m2 of floor area. Studies included in our analysis were unanimous in showing emissions reductions when building with mass timber compared to conventional materials. Scaling-up low-carbon construction, assuming mass timber is substituted for conventional building materials in half of expected new urban construction, could provide as much as 9% of global emissions reduction needed to meet 2030 targets for keeping global warming below 1.5⁰C. Realizing the climate mitigation potential of mass timber building could be accelerated by policy and private investment. Policy actions such as changing building codes, including mass timber in carbon offset crediting programs and setting building-sector-specific emissions reduction goals will remove barriers to and incentivize the adoption of mass timber. Private capital, as debt or equity investment, is poised to play a crucial role in financing mass timber building.
... 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 performance such as lower greenhouse gas (GHG) emissions compared with alternative concrete buildings, although different study periods or system boundaries were applied (Robertson et al 2012;Durlinger et al 2013;Grann 2013;Bowick 2015Bowick , 2018. ...
Article
The building and construction sector is a major contributor to human environmental impact on the planet. It follows that the sector's contribution is also crucial for transition towards a low carbon society and circular economy (CE). Mass timber products, are one of the sustainable alternatives to traditional building materials and have led to the recent revolution in timber construction. While environmental benefits of mas timber manufacturing and construction is well documented the end-of-life (EOL) and the post-EOL options for mass timber buildings, their environmental benefits and CE potential are discussed much less. Short history of construction technology involving prefabricated mass timber panels compared to traditional building types results in virtually no documented cases of panelized mass timber structures reaching the EOL stage and no practical examples of incorporating CE concepts in such projects. In this study, a two-step systematic literature review was used, to define and classify 23 CE-based governing principles from six categories in the construction industry, and to use those principles to analyze the state-of-the-art circular approach in mass timber research. The study covered a total of 90 papers, of which 68 focused on the general construction industry and 22 specifically on the mass timber construction. Results of this review suggest substantial gaps in knowledge and pressing research needs for the development of holistic approaches to prepare the mass timber construction for circular economy.
Article
In this study, the life cycle environmental implications of modular multi-storey building with cross-laminated timber (CLT) volumetric elements are analysed, considering the product, construction, service life, end-of-life and post-use stages. A bottom-up attributional approach is used to analyse the environmental flows linked to the global warming potential (GWP), acidification potential (AP) and eutrophication potential (EP) impacts of the building for a 50-year reference study period. The result shows that the building’s life cycle impacts can vary considerably, depending on the energy production profile for the operation of the building. The product, construction and end-of-life stages constitute a significant share of the life cycle impacts, and the importance of these stages increase as the energy production profile evolves towards a low-carbon energy mix. For the GWP, the product and construction stages constitute 13% of the total life cycle impact when the operational energy is based on a coal-based marginal electricity. The contribution of this stage increases to 81% when electricity is based on a plausible long-term Swedish average mix. The patterns of the life cycle EP and AP impacts are also closely linked to the energy production profile for the assessment. The analysis shows that a 5% reduction in the GWP impact in the product stage is achievable with emerging solutions for the improved structural design of CLT buildings. This study highlights the need for strategies to improve the life cycle environmental profile of modular CLT buildings. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
Article
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This paper aims to investigate the energy saving and carbon reduction performance of cross-laminated timber residential buildings in the severe cold region of China through a computational simulation approach. The authors selected Harbin as the simulation environment, designed reference residential buildings with different storeys which were constructed using reinforced concrete (RC) and cross-laminated timber (CLT) systems, then simulated the energy performance using the commercial software IES™ and finally made comparisions between the RC and CLT buildings. The results show that the estimated energy consumption and carbon emissions for CLT buildings are 9.9% and 13.2% lower than those of RC buildings in view of life-cycle assessment. This indicates that the CLT construction system has good potential for energy saving when compared to RC in the severe cold region of China. The energy efficiency of residential buildings is closely related to the height for both RC and CLT buildings. In spite of the higher cost of materials for high-rise buildings, both RC and CLT tall residential buildings have better energy efficiency than low-rise and mid-rise buildings in the severe cold region of China.
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As part of the Integrated Carbon Metrics project, which comprehensively quantifies embodied GHG emissions related to the built environment in Australia, this contribution evaluates construction material replacement scenarios at the economy-wide scale. We investigate the potential use of Engineered Wood Products (EWPs) in new building stock to assess the carbon outcomes of a potentially significant shift in the use of construction materials. This becomes increasingly relevant as Australia moves forward with augmenting the National Construction Code to allow the construction of mid-rise buildings utilizing timber. The selection of low-carbon and sustainable building materials is crucial in reducing the built environment's carbon footprint. The main objective of the replacement scenario analysis is to assess the potential reduction in future GHG emissions by replacing the use of reinforced concrete with EWPs. The scenarios include the comparison of mid-rise buildings (10-story) with standard reference buildings (using reinforced concrete) at the national scale. The analysis considers the full cradle-to-gate carbon footprint of construction materials embedded in buildings. Since the scenarios are implemented in an input-output model of the Australian economy, changes in the use of construction materials can also be evaluated with respect to indirect effects on industries involved in the production chain of these materials as well as their respective GHG emissions.
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Australia accounts for just 0.33% of the world's population yet it is one of the highest emitters of greenhouse gas (GHG) emissions per capita in the world. The construction sector is a substantial area for mitigation efforts in Australia because of its economic importance and its involvement with indirect GHG emissions, i.e. those embodied in construction supply chains, including construction materials and electricity use. While the majority of policies and regulations focus on reducing direct emissions from buildings, more attention needs to be paid to the embodied emissions of the whole sector as these can take up anywhere between 10% and 97% of the whole life-cycle carbon emissions.
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This article reviews proposed technical approaches for the manufacture and use of alternatives to Portland Cement Clinker as the main reactive binder component for ordinary concrete construction in non-specialty applications, while giving lower net global CO2 emissions in use. A critical analysis, taking into account a wide range of technical considerations, suggests that, with the exception of alkali-activated systems, (treated in a separate paper in this issue,) there are only four classes of alternative clinker system that deserve serious attention with respect to global reductions in concrete-related CO2 emissions:
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This paper reports on a study examining the potential of reducing greenhouse gas (GHG) emissions from the building sector by substituting multi-storey steel and concrete building structures with timber structures. Life cycle assessment (LCA) is applied to compare the climate change impact (CC) of a reinforced concrete (RC) benchmark structure to the CC of an alternative timber structure for four buildings ranging from 3 to 21 storeys. The timber structures are dimensioned to meet the same load criteria as the benchmark structures. The LCA comprises three calculation approaches differing in analysis perspective, allocation methods, and modelling of biogenic CO2 and carbonation of concrete. Irrespective of the assumptions made, the timber structures cause lower CC than the RC structures. By applying attributional LCA, the timber structures are found to cause a CC that is 34-84% lower than the RC structures. The large span is due to different building heights and methodological assumptions. The CC saving per m² floor area obtained by substituting a RC structure with a timber structure decrease slightly with building height up to 12 storeys, but increase from 12 to 21 storeys. From a consequential LCA perspective, constructing timber structures can result in avoided GHG emissions, indicated by a negative CC. Compared to the RC structures, this equal savings greater than 100%.
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Radical modernization of the greenhouse gas emitting industrial sectors is indispensable for transition to a low-carbon economy. The iron and steel industry accounts for 6.7 % of the global anthropogenic carbon dioxide emissions. Futures of iron and steel industry based on various market penetration scenarios for best available and innovative technologies have been modelled and analyzed against the climate change mitigation targets identified by the International Energy Agency for keeping the global warming within 2C. Plausible modernization pathways have been studied revealing a possibility of achieving the levels of CO2 emissions consistent with the climate targets by 2030-2040. However, reaching of the targets established for 2050 requires disruptive innovations in a synergy with carbon capture and storage/utilization, enhanced material efficiency and greater share of recycled steel production. The need for international collaboration to facilitate development and commercialisation of eco-innovations has been revealed. International instruments shall be applied in order to deliver incentive for modernisation, to boost carbon investment mechanisms and to ensure borderless technology transfer.
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Greenhouse gas (GHG) is a major air emission pollutant that creates environmental burden in buildings. Timber buildings are gaining notable popularity in the building industry due to life cycle environmental and economic benefits over conventional buildings. However, little or no studies have made attempts to compare greenhouse gas emission variations in timber and concrete buildings during the construction stage. Knowledge of emission at the construction stage is critical for passionate contractors who wants to maintain an environmental friendly built environment. The study presented in this paper aims to compare GHG emissions and energy consumptions during timber and concrete building construction. A process based quantitative assessment is conducted for evaluating emissions from materials, equipment and transportation stages. The comparative results of the study indicated that use of timber can reduce embodied emissions as well as transportation emissions during the construction stage. Scenario analyses results comprehends that recycling of materials and use of regional materials influence GHG emissions the most while transportation distance has medium effect on total GHG emissions at the construction stage of timber building. The results of the study are important in aggregate level decision making of timber and concrete buildings. Further studies are encouraged on conducting comprehensive assessment of different timber usages in a building to investigate the GHG emission variation.
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Developing tools and methodologies for the evaluation of sustainable buildings is essential to promote transparency in building design community. Building sustainability includes attributes from the built, natural and social systems, and inherently requires a series of trade-offs. These complex and often competing priorities require consideration at each stage of a building's life-cycle. A total of 24 environmental, social and economic indicators were developed and applied to three alternative building systems, e.g., cross laminated timber (CLT), steel and reinforced concrete. The goal of this study is to demonstrate the use of a multi-attribute decision support system (MADSS) that uses a series of indicators, assigns numerical values to these indicators, and allows for systematic evaluation and ranking of alternatives. A case study approach was used to demonstrate the utility of the MADSS approach to identify 'hotspots' for the three building systems. Portland Oregon was selected as the location for the alternative buildings. The functional unit for this study was a mixed use nine story building with an area of 19,000 square feet. CLT building was found to have a higher rank compared to concrete and steel in all three attributes of environmental, economic and social sustainability This study is intended to serve as a demonstration of the MADSS tool for building systems and identify hotspots in the various indicators utilized for sustainability evaluation. The ranking of environmental, social and economic attributes of building materials on specific indicators will vary with the interests of stakeholders, and building location, type, design or other factors.
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This paper presents lab-scale flash carbonization (FC) experiments under elevated pressure using Norwegian wood as a feedstock. The silicon and ferrosilicon industry of Norway has been urged to reduce fossil CO2 emissions by increasing the use of charcoal as a substitute for coal and coke in the production process. Because charcoal is not produced in Norway, large amounts of it are imported from south Asia. Norway now intends to produce charcoal locally using optimum carbonization techniques from local biomass and forestry waste. That is where the pressurized FC experiments come in. Birch, spruce and corresponding forest residues (FRs) were carbonized, enabling the analysis of the impact of pressure and FC canister insulation on their respective fixed carbon yields. FRs proved to be proper to make charcoal, because fixed carbon contents of 80% could be achieved at moderate pressures. The fixed carbon yields of spruce and birch wood reached over 90% of their theoretical values. The high charcoal yields can result in remarkable cost savings for the metallurgical industry while, at the same time, making excessive deforestation unnecessary. The use of coal will soon be abandoned in the ferrosilicon industry, and charcoal "mines" could become an obvious choice.