Life Cycle Assessment and Cost Analysis of Mid-Rise Mass Timber vs. Concrete Buildings in Australia

Abstract

The building and construction industry is one of the largest greenhouse gas producers, accounting for 39% of global emissions, most of these coming from concrete and steel. Mass timber construction (MTC) potentially offers a sustainable alternative to these traditional building materials. However, more research is needed to establish the sustainability credentials of MTC relative to traditional concrete and steel structures, especially for mid-rise structures. The aim of this study is to evaluate the environmental and cost performance of mid-rise mass timber buildings by conducting a life cycle assessment (LCA). The LCA uses a cradle-to-cradle approach, considering the global warming potential (GWP), freshwater use (FW), and total use of non-renewable primary energy resources (PENRT). Results indicated that mid-rise mass timber buildings have significantly lower impacts than concrete buildings, with their GWP approximately 30 times lower, FW about 20 times lower, and PENRT reaching a negative value. Additionally, the cost analysis revealed that MTC buildings can be cheaper to build and thus possibly more profitable than concrete buildings. These findings establish mass timber as a viable and sustainable option for the future of Australia’s construction industry.

1. Introduction

Urban areas such as cities are responsible for around 72% of human-induced global carbon dioxide emissions, with the building and construction sector responsible for around 39% of energy and process-related carbon dioxide emissions [1,2]. Concrete and steel have dominated the construction industry due to their performance in large-scale projects across criteria such as cost, fire resistance, and structural adequacy. However, the concrete industry alone accounts for 7% of global carbon dioxide emissions, while steel is responsible for 6–9% of global emissions [3,4]. Although significant improvements have been made to the environmental performance of common building materials such as concrete and steel, they still embody large amounts of carbon dioxide emissions during their production [5]. Australia accounts for only 0.33% of the world’s population yet is one of the highest fossil and greenhouse gas emitters per capita in the world [6]. Buildings account for around 18% of direct carbon emissions in Australia, so the selection of suitable materials and construction methods is vital to reducing emissions [7].

Mass timber offers a promising solution to the limitations of traditional construction materials, serving as a viable alternative for core building elements. There has been a growing interest in the use of MTC due to its technical capabilities, cost-competitiveness, and positive environmental properties compared to concrete and steel [8]. Mass timber has been shown to meet all the standard structural requirements such as fire, wind, and seismic capabilities, even outperforming traditional building materials in many ways [9]. In addition to its technical performance, mass timber can sequester carbon over its life cycle while also having the potential to lead to fewer emissions during the construction and operational stages of buildings [8].

Since the completion in 2012 of Lendlease’s Forté, a 10-storey mass timber building, the popularity of mass timber construction has been steadily rising in Australia. The Forté building showcased mass timber’s excellence and innovation and received a 5 Star Green Star As-Built rating by the Green Building Council of Australia [10]. Other examples of MTC include the Kind Street Timber Tower, a 10-storey engineered timber building built 20% faster than conventional buildings, and Gillies Hall, Australia’s first mid-rise mass timber student accommodation building [11]. Australia has updated building codes to accommodate MTC, providing an opportunity to rethink urban structures and systems [12].

Most of Australia’s major cities are growing at rates faster than many developed cities internationally, putting pressure on these cities to densify and/or expand [13]. The growing population poses a threat to the liveability and sustainability of urban life in Australia. The population in Australia is largely concentrated in urban hubs with more than 76% of the population living in eight major cities [13]. Between 2010 and 2020 the major cities grew by 3.1 million people, accounting for 84% of the country’s total population growth [13].

Despite the growing population in Australia, it has some of the lowest population densities in the world. For example, the city of Melbourne is roughly three times the area of London yet has a third of its population [14], mostly because apart from Melbourne’s inner city, the rest of Melbourne continues to sprawl out with low-rise buildings. The current urban environment needs to support higher density development to continue to sustain the large population growth in Australia’s major cities. While Australia’s major cities continue to expand, so do their impacts, with increases in urban heat, congestion, pollution, and waste, and impacts on the natural environment [13]. Encouraging high-density development through mid-rise mass timber buildings in Australia is crucial for addressing population growth and climate change while enhancing urban wellbeing and livability.

To help accelerate the use of mass timber, the Australian government has launched the Cleaner Energy Finance Corporation (CEFC) Timber Building Program to encourage the transformation of medium and high-rise buildings through funding for eligible projects with an AUD 300 million finance fund [15]. The federal government program, along with advancements in MTC, have brought about the planned construction of multiple tall mass timber hybrid buildings in Australia. Some examples of these are the Atlassian HQ in Sydney, a 40-storey hybrid timber tower with a steel and glass façade, and the C6 tower in Perth, which will be the tallest commercial hybrid timber tower in the world [16]. Tall buildings, however, make up only a small portion of the building industry in Australia, with an estimated 80% of office buildings alone being mid-rise [17]. Australia’s current focus on tall hybrid timber buildings, despite their challenges in gaining building approval, overlooks the potential of mid-rise mass timber structures, which could significantly transform various building types and contribute to sustainability goals.

Despite its numerous advantages, the widespread adoption of mid-rise mass timber faces significant challenges. Factors such as a lack of education within the construction industry, resistance to change from traditional materials, and insufficient media attention compared to high-rise projects impede its adoption [18]. Historically, sourcing materials for MTC has also been a deterrence, but the emergence of local manufacturers such as XLam and Wood Solutions suggests promising growth in domestic supply capabilities that should overcome these concerns [19,20]. Consequently, perhaps the main inhibitor to a rapidly expanding use of MTC for mid-rise buildings in Australia is uncertainty in the construction industry about the relative environmental benefits of switching to MTC and whether such a shift would be cost-effective.

The aim of this project is to evaluate the environmental and cost impacts of mid-rise MTC compared to concrete through a comprehensive cradle-to-cradle life cycle assessment (LCA) analysis. Unlike prior studies limited to cradle-to-site, this research fills a knowledge gap by examining mid-rise construction’s holistic performance, particularly in Australia, aiming to provide updated insights into its environmental footprint beyond carbon emissions. The study has the following objectives:

• To quantify and compare the environmental and costs impacts of MTC vs. traditional concrete and steel builds for mid-rise structures using a cradle-to-cradle life cycle approach;
• To identify critical stages of the building’s life cycle where environmental and cost impacts are most significant, and inform the competitiveness of mid-rise mass timber buildings in the construction industry and promote their adoption in Australia.

2. Materials and Methods

This section describes the methods utilized to conduct a life cycle analysis (LCA) and a cost analysis of mass timber and concrete mid-rise buildings located in Melbourne, Australia. The aim of the use of the LCA method was to gain a better understanding of the environmental impacts and differences between mid-rise mass timber and concrete buildings. A cradle-to-cradle LCA model was used to ensure all aspects of the building’s life were taken into consideration beginning from the extraction of raw materials and concluding with the energy recovery and reuse possibilities for both building types. To determine what would be needed in the construction of an eight-storey building, a bill of materials was adapted from an LCA study conducted by Gu et al. [21], which included a bill of materials for an eight-storey building for both mass timber and concrete construction.

There were several alterations made to the original bill of materials. First, the amount of glulam required for the columns and beams was reduced because the required amount quoted by Gu et al. [21] was considered excessive in comparison to other studies. Conservative estimates indicate that to replace reinforced concrete columns and beams, the amount of glulam in m³ required would be one and a half times that of the concrete required; thus, the amount of glulam required was reduced to that amount. Additionally, mineral wool and fiberglass mats (both used as insulation) were excluded from the bill of materials because they are required for both mass timber and concrete buildings in similar quantities and so would not represent a point of difference between the two. Similarly, the PE (polyethylene) vapor barrier was also removed from the bill of materials because the amount of PE vapor barrier required was close to equal for both buildings, and again would not represent a point of difference. All of the remaining materials and amounts utilized remained the same as those presented by Gu et al. [21]. The LCA was conducted with a life cycle of 75 years following the EN 15978 [22] and EN 15804 [23] standards to ensure all stages were assessed correctly.

Table 1. List of sources for the LCAs.

Stage	Purpose	Source
A1–A3	Bill of Materials	Gu et al. [21].
	Concrete	EPD Australasia—Average of Boral, Barro and Adbri [24,25,26].
	Glulam	EPD Australasia—Wood Solutions [27].
	Rebar	EPD Australasia—Australian Reinforcing company [28]
	Steel stud (1.15 mm, #681)	EPD Australasia—Rondo [29]
	CLT	EPD Australasia—Xlam [30]
	Gypsum Board (Fireshield 13 mm)	EPD Australasia—Siniat—plasterboard [31]
	Foam insulation	EPD Australasia—Metecno [32]
	Acoustic insulation (Absorb black 25 mm)	EPD Australasia—Martini [33]
A4	Truck carbon emissions calculator	Greenstar [34]
	Concrete transportation	EPD Australasia—Hanson [35]
	Imported CLT transportation	Durlinger et al. [36], carboncare.org [37]
	Glulam transportation	EPD Australasia—Woodsolutions [27]
A5	Total diesel equation	Greene et al. [38]
	Diesel GWP coefficient	Department of Climate Change, Energy the Environment and Water [39]
C1	MTC vs. concrete demolition	Duan et al. [40]
C2	Transport to waste disposal	AusLCI Carbon Emission Factors [41]
C3−D	Concrete	EPD Australasia—BGC Concrete [42]
	Glulam	EPD Australasia—Wood Solutions [27]
	Rebar	EPD Australasia—Australian Reinforcing Company [28]
	Steel stud	EPD Australasia—Rondo [29]
	CLT	EPD Australasia—Xlam [30]
	Gypsum board	EPD Australasia—Siniat [31]
	Acoustic insulation	EPD International—Interfloor crumb rubber underlay EPD [43]

provides the sources of all the data used through every stage of the life cycle analysis. A cost analysis was also conducted in conjunction with the LCA to further understand the costs associated with constructing both a timber and concrete building; the sections below further describe the methods utilized for each stage in detail.

2.1. Product Stage

According to standards EN 15978 and EN 15804, the production stage marks the initial phase in the building life cycle and is divided into three distinct modules. Module A1 concerns the raw material supply, Module A2 is the transport of raw materials, and Module A3 is the manufacturing of a product for construction use. Equation (1) was used to calculate the global warming potential (GWP), freshwater use (FW), and total use of non-renewable energy resources (PENRT) totals for each material used in the building designs:

$${\mathrm{E}}_1=\mathsf{\Sigma }{\mathrm{f}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}} \ast {\mathrm{M}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}}$$

(1)

where f_material represents the environmental impact factors of GWP, FW, and PENRT per unit of the specified material, while M_material represents the quantity of that material used within the buildings. The environmental impact factors for this stage were sourced from environmental product declarations (EPDs) corresponding to each material used in the building designs, covering Modules A1 through to A3. For the calculation of the environmental impact of concrete, the impact factors were taken as an average of three different concrete suppliers. The environmental impact factors for all other materials were taken from one EPD per material (Table 1).

2.2. Construction Stage

Transportation to site, also referred to as Module A4, covers the global warming potential emissions from transporting the manufactured product to the construction site. Module A4 used a mixture of environmental product declarations (EPDs) from Table 1 and Equation (2) to calculate the global warming potential contributions:

$${\mathrm{E}}_2=\mathsf{\Sigma }\mathrm{D}\cdot {\mathrm{M}}_{\mathrm{l}\mathrm{o}\mathrm{a}\mathrm{d}}\cdot {\mathrm{f}}_{\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{n}\mathrm{s}\mathrm{p}\mathrm{o}\mathrm{r}\mathrm{t}}$$

(2)

where D is the total distance travelled, M_load is the mass of the hauled material in tonnes, and f_transport is the emission factor of the transport mode (kg CO₂e/tkm). The transport stage considered environmental impacts for concrete, steel, and mass timber components. The construction site was in Melbourne, so supplier distances were based on previously used EPDs. For concrete, it was assumed a supplier was within 20 km of the build site. For all road transport, a truck with a 16–28 tonne gross weight was used, except for concrete, where specific truck details were unknown, and thus EPD emission factors were used. The emission factor for a 16–28 tonne truck was taken from AusLCIv1.42.

Two sourcing scenarios for cross-laminated timber (CLT) were considered: local and imported from Austria. The GWP for CLT imported from Austria was based on the work of Durlinger et al. [36]. In their study, they showed that CLT travels from Katsch an der Mur, Austria, to Koper by truck, then by ship to Melbourne via Singapore, totalling 19,433 km [36]. The ship’s GWP was calculated using carboncare.org, based on shipment weight and route. The truck distance from the Port of Melbourne to the site was calculated using the same method as for locally sourced CLT.

The construction and installation phase (Module A5) details the GWP from activities during building and construction. Equation (3) was used to calculate the total diesel requirements, and Equation (4) was used to calculate the total GWP of each building:

$$\mathrm{V}=0.000037 \ast {\mathrm{M}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}} \ast \mathrm{h}+{\displaystyle \frac{{\mathrm{M}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}}}{500}}+0.83$$

(3)

$${\mathrm{E}}_3={\mathrm{V}}_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{l}} \ast {\mathrm{f}}_{\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{s}\mathrm{e}\mathrm{l}}$$

(4)

where M_material is the mass of materials in kg, h is half the building height in meters, and V_diesel is the total diesel required and is calculated in Equation (3), while f_diesel is the GWP emission factor for diesel. These formulae only considered the crane’s diesel requirements. Previous LCA analyses showed no major difference in earthworks between MTC and concrete buildings, so that phase was excluded. Other construction elements contributing to GWP were also excluded due to limited information. The main difference was crane usage, influenced by construction speed and material mass. To calculate the diesel impact, the mass of materials hauled by the crane was calculated from the bill of materials and material densities.

2.3. Use Stage

The use stage covers environmental impacts from building operation until end of life, as defined by EN 15978 and EN 15804. The use stage includes seven modules: use (B1), maintenance (B2), repair (B3), replacement (B4), refurbishment (B5), operational energy use (B6), and operational water use (B7). The LCA excluded the use stage following the findings from past studies where Eslami et al. [24] and Forest and Durlinger [36] found Module B1 impacts were similar for both types of buildings. Maintenance, repair, replacement, and refurbishment were also assumed to have negligible differences by building type because the LCA focuses on the main structural elements of the buildings. Both buildings are considered to have the same energy class, making operational energy and water use identical, and thus these were excluded from this study [36,44].

2.4. End-of-Life Stage

The end-of-life stage involves four modules: deconstruction (C1), waste transportation (C2), waste processing (C3), and disposal (C4) per EN 15978 and EN 15804. A cradle-to-cradle approach extends evaluation to include reuse, recovery, and recycling (Module D). Total GWP for each building was calculated using Equation (5):

$${\mathrm{E}}_4={(\mathrm{f}}_{\mathrm{b}\mathrm{u}\mathrm{i}\mathrm{l}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g}} \ast {\mathrm{A}}_{\mathrm{b}\mathrm{u}\mathrm{i}\mathrm{l}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g}})$$

(5)

where f_building is the GWP emission factor, and A_building is the total building area in m². The GWP for deconstruction was sourced from Duan et al. [45], which indicated emission factors per m² for both buildings.

The transport to waste processing, otherwise known as Module C2, covers the emissions from transporting the construction waste from the building site to a waste processing site. Module C2 used Equation (2) to calculate the global warming potential contributions. For the calculation of the global warming potential, it was assumed that a truck with a 16 to 28 tonne gross weight will be used to transport the materials. The emission factor for a 16 to 28 tonne truck was taken from AusLCIv1.42. The buildings have a design life of 75 years and it was assumed that there would be a suitable location within 30 km of the site in Melbourne.

The waste processing, disposal, and reuse, recovery, and recycling modules, also referred to as modules C3, C4, and D, respectively, are the final stage of the life cycle assessment. Modules C3, C4, and D cover the environmental impact contributions of waste processing and the potential reuse, recovery, and recycling of specific material. Equation (6) was used to calculate the total environmental impact for each end-of-life scenario:

$${\mathrm{E}}_5=\mathsf{\Sigma }{(\mathrm{f}}_1 \ast {\mathrm{M}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}})+({\mathrm{f}}_2 \ast {\mathrm{M}}_{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}})$$

(6)

where f₁ represents the environmental impact factors GWP, FW, and PENRT per unit of the specified material for Module C3, f₂ represents the environmental impact factors GWP, FW, and PENRT per unit of the specified material for Modules C4 and D, and M_material represents the quantity of that material used within the buildings. The data collected to find the GWP, FW, and PENRT totals were based on multiple environmental product declarations (EPDs) and are summarized in Table 1 for each material type used in the building designs.

The concrete building was split into two scenarios, landfill and recycling, while the MTC building was split into four scenarios, landfill, energy recovery, recycling, and reuse. The landfill scenarios for both concrete and MTC take f₂ as the environmental factor for the C4 Module, whereas the concrete recycling scenario and MTC recycling, reuse, and recovery scenario take f₂ as the environmental factor for Module D.

For the concrete recycling scenario, each material in the building was assumed to be recycled except for the foam insulation board, and because no EPDs could be found to cover a recycling scenario, it was assumed to go to landfill. The energy recovery, recycling, and reuse scenarios of MTC buildings only apply to the timber components and assume all other materials were recycled. The energy recovery scenario involved energy recovery through shredding and combustion, offsetting energy from natural gas with options including coal or electrical replacement. The reuse scenario involved the direct reuse of the timber components from the building without any further processing. The final scenario, recycling, involves downcycling the timber components into wood chips to be utilised in other products. These scenarios were based on assumptions made by their equivalent EPDs.

2.5. Totals

Equation (7) is used to calculate the environmental impact totals for both concrete and mass timber construction (MTC):

$${\mathrm{E}}_{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}=\mathsf{\Sigma }{\mathrm{E}}_1+{\mathrm{E}}_2+{\mathrm{E}}_3+{\mathrm{E}}_4+{\mathrm{E}}_5$$

(7)

where E₁ is the product stage total environmental impact, E₂ is the total environmental impact of both transportation modules, E₃ is the total environmental impact for the construction/installation stage, and E₄ is the total environmental impact of the end-of-life disposal, reuse, recovery, and recycling. The calculated totals were split up into different best and worse scenarios for each of the different building-type cases, with the first case being the concrete building, the second being the MTC building, and lastly, the MTC building with imported CLT. Totals were calculated for GWP, FW, and PENRT.

2.6. Cost Analysis

The cost analysis was conducted based on a previous cost analysis completed by Wood Solutions on an eight-storey residential building in Australia [46]. However, there were some alterations made to the cost analysis given in that report. First, wall finishes were excluded from the results because they do not contribute to differential costs between the building types. Next, the cost of the foundation was added to the analysis because the mass timber building does not require a foundation as thick as the concrete building does. Third, the construction costs including labour, site management, site sheds, and any equipment required were considered to be AUD 52,000 per week for the whole duration of construction for both buildings. Finally, it was conservatively assumed that six weeks would be saved in construction time for the mass timber building, thus reducing the construction time from twelve months for the concrete building to ten and a half months for the mass timber building.

3. Results

The following section outlines the results of the life cycle and cost assessments of the mass timber and concrete mid-rise buildings in Melbourne, Australia. Environmental impact factors of both buildings were calculated and compiled in accordance with the methods described above. The findings are presented as graphs, illustrating the environmental impacts for both building types during each stage of the life cycle assessment.

3.1. Product Stage

The product stage analysed the global warming potential (GWP), freshwater use (FW) and the total use of non-renewable primary energy sources (PENRT) for the production of materials required for the reinforced concrete and mass timber construction (MTC) buildings. The bill of material quantities for each building is shown in

Table 2. Bill of material quantities.

Assembly	Material	MTC Quantity	Concrete Quantity	Unit
Columns and Beams	Concrete 40 MPa	n/a	93	m3
	Glulam	140	n/a	m3
	Rebar	n/a	59	tonnes
Exterior Walls	Steel stud	n/a	738	kg
	CLT	172	n/a	m3
	13 mm Gypsum board	1638	1638	m2
	70 mm Foam insulation	n/a	1638	m2
Floors	25 mm Acoustic insulation	4115	n/a	kg
	CLT	1437	n/a	m3
	Concrete 40 MPa	790	2293	m3
	Rebar	5	42	tonnes
Foundation	Concrete 40 MPa	367	674	m3
	Rebar	12	20	tonnes
Interior Walls	CLT	1152	n/a	m3
	Concrete 40 MPa	n/a	516	m3
	13 mm Gypsum board	13,724	24,041	m2
	Rebar	n/a	73	tonnes
	Steel stud	8112	16,302	kg

Note: n/a = not applicable, MTC = mass timber construction, CLT = cross-laminated timber.

. The materials’ characteristics as well as their quantities were used in calculating each environmental impact.

Figure 1a illustrates the total GWP for concrete and MTC buildings, showing MTC’s negative GWP compared to concrete’s positive GWP. In the MTC building, the utilization of CLT and glulam combined reduced the GWP by a total of −1,415,328 kg CO₂, signifying the beneficial climate impact of including MTC components within the building.

The total freshwater usage and total use of non-renewable primary energy resources are depicted in Figure 1b and Figure 1c, respectively. In both cases, MTC outperformed the concrete structures, with 17% lower freshwater use by the MTC building and 500,000 fewer MJ of non-renewable energy resources consumed by the MTC building relative to that of the concrete structure.

3.2. Construction Stage

The GWP of the transport required to get materials to the site location is depicted in Figure 2a. Per the methods section, the concrete building components were considered to be transported from Metropolitan Melbourne, local CLT and glulam were considered to be transported from Regional Victoria, and imported CLT was considered to be transported from Austria. The concrete building exhibited the lowest global warming potential (GWP) for transportation. Locally sourced MTC materials demonstrated five times the GWP of the concrete building, while imported MTC materials showed 15 times the GWP of the concrete building.

The GWP of construction, specifically the diesel requirements associated with crane usage for the concrete and MTC buildings, is depicted in Figure 2b. The MTC building exhibited the lowest GWP for construction, releasing close to half the GWP emitted by the concrete building.

3.3. End-of-Life Stage

Figure 3a depicts the GWP of the deconstruction of the concrete building in comparison to the MTC building. The concrete building produced the highest GWP, exhibiting more than double the GWP of the MTC building. Figure 3b depicts the GWP of transportation to processing or disposal sites. The concrete building had the highest GWP, approximately 40% higher than the MTC building. The results show that a total of 10,663 kg of CO₂e emissions were generated from the concrete components of the MTC building, accounting for 66% of the total emissions for MTC.

The data presented in Figure 4a–c highlight the GWP, FW, and PENRT totals associated with different end-of-life scenarios including landfill, energy recovery, recycling, and reuse. The MTC buildings consistently produced the highest GWP for each end-of-life scenario, where the GWP for the best-case scenario was approximately eight times higher than the concrete landfill scenario.

The MTC reuse stage in Figure 4b produced the best freshwater use results, using approximately six times less water per m³ than the best concrete building scenario. The MTC energy recovery scenario was the best performing scenario with respect to PENRT, using approximately 20 times fewer Megajoules than the best concrete building scenario (Figure 4c).

3.4. Totals

Figure 5a–c show the combined GWP, FW, and PENRT results for the life cycle assessment from cradle to cradle. Results show that the MTC building performs better in every scenario compared to the concrete building, with the exception of PENRT totals for both worst case scenarios. The concrete building’s total GWP was approximately 30 times higher than the MTC building, its total FW was approximately 20 times more than the MTC building and the total PENRT for the MTC building was negative for its best-case scenario.

3.5. Cost Analysis

The cost analysis of the elements that differentiated between the building types indicated that close to AUD 480,000 is saved when using mass timber in a building rather than concrete.

Table 3. Cost analysis of the differentiating elements between the two mid-rise building types.

Assembly	MTC	Concrete	Variance
Columns and beams	$34,935	$365,644	−$330,709
Exterior walls	$518,082	$416,165	$101,917
Floors	$2,539,961	$1,810,398	$729,563
Foundation	$364,350	$537,441	−$173,091
Interior walls	$1,286,436	$1,224,522	$61,914
Roof	$233,100	$356,617	−$123,517
Ceiling finishes	$0	$459,085	−$459,085
Termite protection	$25,000	$0	$25,000
Construction costs (labour, etc.)	$2,392,000	$2,704,000	−$312,000
Total	$7,393,864	$7,873,872	−$480,008

summarizes the prices broken down by material costs and construction costs for each element of the two buildings. The cost analysis indicates that the initial material price for both buildings is close to AUD 5,000,000 and that the majority of the savings for the MTC building comes from the ceiling finishes, columns and beams, and reduced construction time.

Six weeks was saved in construction time for the MTC building, reducing the construction time from twelve months for the concrete building to ten and a half months for the MTC building, ultimately reducing the total cost by around AUD 300,000 due to savings in labour, site management, site sheds, and any equipment required such as cranes and scaffolding. The cost analysis total indicated that the MTC building is cheaper to construct than the concrete building with a saving of 6%, or AUD 480,000, attained when constructing the building with MTC.

4. Discussion

This study aimed to evaluate the environmental and cost performance of mid-rise mass timber buildings and identify specific stages with the most significant impacts. The analysis seeks to inform stakeholders and enhance the competitiveness of mass timber buildings in Australia. The results showed that mid-rise mass timber buildings perform significantly better in several key areas compared to traditional concrete structures. The following section discusses the findings of the life cycle assessment and uses the current literature to support these findings, highlighting the strengths and limitations of each building type for each life cycle stage to contribute to informed decision making in the construction industry.

4.1. Product Stage

In the product stage of the life cycle assessment, three indicators of environmental impact were analysed: global warming potential (GWP), freshwater use, and total non-renewable energy (PENRT). MTC outperformed concrete in all three indicators. Concrete and rebar had negative impacts across all indicators, whereas glulam and CLT showed positive impacts. The MTC building included all four materials, while the concrete building did not include glulam or CLT. The concrete building required over three times the amount of concrete and more than ten times the amount of steel rebar compared to the MTC building, significantly impacting the outcome.

The GWP of the MTC building was negative, indicating CO₂ sequestration, while the concrete building had a large positive GWP, indicating CO₂ emissions. Trees absorb CO₂ through photosynthesis, binding carbon into sugars used for growth while releasing oxygen [47]. Glulam and CLT store more carbon than is emitted during the product stage, including harvesting, transporting, and manufacturing. MTC plantations promote carbon sequestration, as young trees capture carbon as they grow. Trees continue to store carbon until they decompose or are burned. About 50% of a tree is carbon, and decomposition takes many years, so MTC buildings store this carbon once built [40]. These findings confirm Harte’s support regarding MTC’s ability to reduce emissions [8].

Concrete and steel had significant impacts across all environmental indicators, with 90% of the GWP of the concrete building attributed to concrete and steel rebar, resulting in over 1 million additional kgCO₂ emissions compared to the MTC building. Freshwater use also favoured MTC, though the difference was smaller than for GWP. Concrete and steel accounted for 90% of freshwater use in the concrete building, while in the MTC building, 30% was attributed to concrete and steel, and 60% to glulam and CLT. Hardwood glulam used more freshwater than CLT, but using softwood glulam reduced water usage. Glulam and CLT water usage comes from plantations, pressing and curing, and post-lamination treatment [48]. These processes are efficient, and reducing freshwater use in MTC would require significant investment.

Non-renewable energy (PENRT) also favoured MTC, as CLT and glulam required less non-renewable energy per cubic meter than concrete and steel rebar. Less material is needed for MTC buildings, so overall, MTC buildings outperform concrete in PENRT. In addition, wood product production tends to involve biomass energy produced by waste products from the wood-harvesting process (a renewable energy source). This contrasts with the heavy reliance on fossil fuels for the production of concrete and steel. These factors combine to see MTC outperform concrete and steel in the consumption of non-renewable energy. The product stage concluded that MTC outperforms concrete in every stage, proving the superiority of materials like CLT and glulam over concrete and steel, supporting Abed et al.’s [9] argument for industry adoption.

4.2. Transport and Construction Stage

Transportation to the construction site was one area where the concrete building outperformed the MTC building. Concrete and steel required shorter transportation distances (about 30 km) to the construction site due to the availability of suppliers near Metropolitan Melbourne. This reduced fuel consumption, emissions, and logistical complexities, contributing to construction efficiency.

In contrast, MTC, particularly imported mass timber, required longer transportation distances. Mass timber travelled about 300 km to the site, with imported timber from Austria traveling approximately 20,000 km. This underscores the environmental impact of transportation and the importance of local sourcing. Transporting mass timber is challenging due to the difficulty of moving large timber beams and high transportation costs [18]. Imported timber needs specific processing, handling, and wrapping due to container size limitations. Local production capabilities and government incentives like the Cleaner Energy Finance Corporation (CEFC) Timber Building Program have facilitated the transition to local supply chains. This reduces the reliance on imported goods and promotes the use of regional suppliers.

The recent completion of Australia’s first mass timber building under the CEFC program in 2023, using only local products, showcases the feasibility and benefits of local sourcing [49]. Local manufacturing reduces transportation distances and fosters economic growth, job creation, and regional development [50]. Local mass timber production supports both rural and urban economies, offering employment and mitigating climate change. XLam’s establishment of the pioneering CLT manufacturing plant in 2017 served as a catalyst for local production, reducing the nation’s dependence on imported products [19]. An increase in demand for mass timber will provide economic incentives to invest in forest plantations [51].

Australia’s forestry supply chain supports domestic and export markets, vital for many rural communities [52]. While concrete is expected to outperform mass timber in transportation to construction sites, transportation is a small component of the overall environmental impact. However, the stagnant growth in new plantations threatens future local mass timber supply. Presently, Australia’s total plantation area is at its smallest since 2003-04, primarily due to the ongoing conversion of hardwood plantations to alternative land uses [53]. This trend poses a looming threat to future local mass timber supply. The forest industry has the potential to address the increasing demand for wood products, while new plantations would support the environment, regional employment, and economic activity, and improve social outcomes [52].

The installation and construction stage showed the MTC building’s superiority, with the concrete building emitting nearly double the CO₂ emissions. The main differentiation was the time of construction, impacting CO₂ emissions from diesel use for crane operations. The concrete building’s material mass was nearly double that of the MTC building, leading to higher emissions. These results highlight the efficiency of constructing mass timber buildings, reducing GWP and construction time and cost.

4.3. End-of-Life Stage

At the end-of-life stage, deconstruction/demolition presented a significant difference in GWP, highlighting the advantages of MTC, which had about half the GWP compared to the concrete building. Due to MTC being a relatively new construction material, there is a knowledge gap regarding its environmental impacts at this stage. The first modern MTC building in Australia was constructed in 2012, so it has not reached end of life [54,55]. Duan et al. [45] used demolition energy data for CLT and concrete to estimate emissions, concluding that CLT has a demolition energy of 0.0359 MJ/kg and reinforced concrete 0.0612 MJ/kg with emissions equalling 7.62 and 3.63 kgCO₂e/m², respectively. These results show the MTC building’s superiority in GWP.

Transportation to waste processing facilities highlighted the advantages of CLT and glulam due to their low density compared to concrete. Concrete, with a density of approximately 2400 kg/m³, is significantly denser than CLT and glulam, which range from 480 kg/m³ to 674 kg/m³ [27,30,56]. Concrete’s high density requires more trips, increasing GWP. Mass timber’s lower transport costs and reduced GWP during transportation contribute to its environmental benefits [57]. However, urban environments like Melbourne can impact fuel consumption due to traffic conditions [58]. The impact of high traffic conditions can result in 1.1 to 1.5 times higher fuel consumption compared to free-flowing traffic [59].

In waste processing, concrete structures benefit from well-established end-of-life strategies, with steel and concrete being highly recyclable [38]. Most life cycle assessment studies of mass timber buildings focus on a cradle to site, or cradle to the construction system boundary, and do not include the end-of-life stage. Predicting the end of life and outcomes beyond the system boundary for mass timber buildings poses challenges because it necessitates forecasting decades into the future, resulting in some uncertainty regarding the accuracy of end-of-life assessments [60]. Mass timber end-of-life scenarios include reuse, recycling, combustion for energy recovery, or landfill [61]. Reusing mass timber extends its lifespan, maximizing sequestered carbon and delaying CO₂ release [62]. The extended lifespan of mass timber also reduces the demand for new timber extraction, mitigating the environmental impacts associated with the timber production process. The reuse of mass timber components also had a large impact on freshwater use, almost making the entire lifecycle, excluding the use stage, water neutral. However, it is important to note that not all mass timber can be recycled because the presence of nail holes or deconstruction-related damage can deem some material unsuitable for reuse [38]. Innovations in modular construction and prefabrication could facilitate easier reuse. While timber is a source of carbon sequestration, once it is incinerated or decays, the sequestered CO₂ stored in the wood is released [60]. Thus, where mass timber cannot be reused, it should be used to produce biomass energy through direct combustion so that it can offset the use of fossil fuels [9,30]. Although it is well-established that wood decomposes very slowly, resulting in minimal carbon loss over decades, the specific decomposition rate of mass timber remains largely unknown due to variations in landfill management practices and climates [63]. In landfills, mass timber decomposes slowly but releases biogenic methane, which has a much higher GWP than CO₂ and thus could have a greater effect on global warming [45]. However, one study in Australia on the decomposition of wood products found that after being buried for 46 years, softwoods and hardwoods had only lost 18% and 17% of their original carbon content, respectively [64]. Other research has shown that only up to 8% of the carbon in wood may be emitted as gas in landfill sites [65]. These studies suggest that the slow rate of timber decomposition minimises immediate carbon emissions.

4.4. Costs

The cost analysis indicated a 6% saving for MTC buildings, nearly AUD 500,000 for a mid-rise MTC building compared to a concrete building. Initial material costs are similar, but construction time savings make MTC more cost-effective. This supports Evison et al.‘s [66] findings but contradicts studies suggesting MTC is more expensive [67]. Variability in results may explain builders’ hesitation in adopting MTC, especially regarding construction phase time savings.

4.5. Limitations

This study’s use of USA-based building design data introduces potential discrepancies, as it may not reflect Australian practices. Modifications were made for environmentally friendly choices, but data constraints limited options. Assumptions about waste processing facilities may not align with real-world scenarios, and uncertainties about end-of-life scenarios highlight the complexity of conducting comprehensive LCAs for mass timber construction. Conservative estimates in this study suggest MTC’s superiority over concrete for mid-rise buildings.

5. Conclusions

This study addresses the urgent need to mitigate urban CO₂ emissions, particularly in Australia where buildings contribute significantly to the high per capita emissions [2,7]. Overall, the life cycle assessment indicated that mid-rise MTC buildings have significantly lower environmental impacts than concrete buildings, with GWP approximately 30 times lower, freshwater use about 20 times lower, and even lower total use of non-renewable energy resources, with MTC having a negative value. Further, the cost analysis revealed potential savings close to AUD 500,000 with MTC, mainly due to faster construction times, suggesting that MTC mid-rise buildings are more profitable than typical concrete and steel mid-rise buildings, with changes in the supply chain in Australia suggesting that MTC mid-rise buildings will be even more profitable in future.

The detailed findings indicated that mid-rise MTC outperformed concrete buildings in the product stage, demonstrating significantly lower global warming potential, freshwater use, and total use of non-renewable energy resources. During the construction stage, MTC exhibited lower GWP from construction activities, although for transportation, the GWP for MTC was higher, particularly for imported materials—although that situation will soon change and represented only a small difference between the building types. At end of life, the MTC building produced higher GWP but performed better in freshwater use and non-renewable energy resources.

These findings suggest that MTC construction should be a preferrable option for the construction industry in Australia, and globally. These structures are both more sustainable and cheaper, indicating that they have both an environmental and commercial advantage over traditional structures. As MTC products are already commercially available, a shift to increased use of MTC as a preferred building material will stimulate further growth in the production of MTC, helping to drive costs even lower, and limiting the potential adverse impacts that come with importing these materials from overseas. Future research should investigate potential barriers to MTC adoption in the Australian construction industry, to help expedite the transition to MTC for mid-rise structures.