Environmental Impact Analysis on Residential Building in Malaysia Using Life Cycle Assessment

The building industry has a significant impact on the environment due to massive natural resources and energy it uses throughout its life cycle. This study presents a life cycle assessment of a semi-detached residential building in Malaysia as a case study and assesses the environmental impact under cradle-to-grave which consists of pre-use, construction, use, and end-of-life phases by using Centre of Environmental Science of Leiden University (CML) 2001. Four impact categories were evaluated, namely, acidification, eutrophication, global warming potential (GWP), and ozone layer depletion (ODP). The building operation under use phase contributed the highest global warming potential and acidification with 2.41 × 103 kg CO2 eq and 1.10 × 101 kg SO2 eq, respectively. In the pre-use phase, concrete in the substructure has the most significant overall impact with cement as the primary raw material. The results showed that the residential building in Malaysia has a fairly high impact in GWP but lower in acidification and ODP compared to other studies.


Introduction
The building industry contributed significantly to the economy and social development. However, it also responsible for the massive impact on the environment due to natural resource consumption and emission released [1]. Roodman et al. [2] suggested that buildings are responsible for world's fresh water withdrawals, wood harvest and material and energy flow that consist of 17%, 25%, and 40%, respectively. Because of the significant effect, the industry gives to the environment, numerous studies have been conducted to reduce the energy consumption and its environmental impact [3].
Life cycle assessment (LCA) has been accepted as a tool to evaluate the environmental impact throughout product life cycle [4,5]. The life cycle of a product or cradle-to-grave, which consists of the pre-use (extraction and acquisition of raw materials, material production, and manufacturing process), use, and end-of-life (EOL), is used to identify systematically and avoid the potential impact on the environment [6]. The introduction of LCA to the building is relatively recent. The first study conducted by Adalberth [7] paved the way for the research in this area. Recent reviews suggested that LCA studies on buildings were conducted all over the world using ISO 14040 series as a basis, but the methodologies were varied [8].
In Malaysia, LCA was initially introduced to assess the sustainability of palm oil production [9]. Since then, it has been used in other industries such as electronics, consumer goods, potable water production, electricity generation, waste management and buildings [10][11][12][13][14][15][16][17][18][19][20][21][22]. Buildings' studies in Malaysia are mainly focused on the impact assessment of different materials. The studies also compared the benefit of integration of an industrialised building system (IBS) to a conventional construction system. Fujita et al. [19] used LCA to estimate CO 2 emission for a concrete and timber based house using an input-output method during the pre-use and operation phase. Omar et al. [20] compared the pre-use phase of two-storey houses with a conventional concrete house and an IBS system house with a precast wall panel using a hybrid method for concrete and steel reinforcement. Wen et al. [21] compared a four-storey conventional apartment in Johor Bahru, Malaysia and a four-storey IBS apartment in Iskandar Malaysia, Johor. Bin Marsono and Balasbaneh [22] compared seven different materials used for the wall of a single-family unit house in Johor, but only global warming potential (GWP) impact category was assessed.
All studies mentioned were conducted without considering a full building life cycle or 'cradle-to-grave', which consist of pre-use, construction, use, and end-of-life (EOL) phases. Moreover, the full environmental impact on residential buildings in Malaysia has yet to be evaluated especially on the global warming impact. The findings from this study can provide useful information to the government agencies and building professionals prior to future developments in terms of the environmental impact of building materials and energy consumption in the building life cycle in Malaysia. Thus, the aim of this study is to estimate the life cycle impact of a residential building in Malaysia from cradle-to-grave in four impact categories specifically on global warming potential (GWP), acidification, ozone depletion (ODP), and eutrophication.

Methods
This study follows the LCA method standardised by an ISO 14040 series, which includes four stages: goal and scope definition, life cycle inventory (LCI), life cycle impact assessment (LCIA), and interpretation [6,23].

Goal and Scope Definition
The functional unit selected in this study was 1 m 2 of gross floor area (GFA), and the building lifespan was assumed to be 50 years as suggested by previous research [24]. The building was a semi-detached house within a residential development area located in the district of Seri Kembangan, Selangor about 25 km from Kuala Lumpur. The construction methods and materials used for the house were similar to other conventional residential buildings in Malaysia, thus without considering any green building characteristics or Green Building Index (GBI) certification [25]. The building frame structures were reinforced concrete with clay bricks as the building envelope. The building size is 246 m 2 GFA with four bedrooms, a living room, a dining room, a maid room, a dry kitchen, a wet kitchen, a family area, a study area and five bathrooms as shown in Figure 1.

System Boundaries
The whole building life cycle was evaluated from cradle-to-grave within specific system boundaries outlined in Figure 2. The construction works involved overall residential development and were not specific to the building such as site clearance works, external works, and infrastructure works were excluded.

System Boundaries
The whole building life cycle was evaluated from cradle-to-grave within specific system boundaries outlined in Figure 2. The construction works involved overall residential development and were not specific to the building such as site clearance works, external works, and infrastructure works were excluded.

System Boundaries
The whole building life cycle was evaluated from cradle-to-grave within specific system boundaries outlined in Figure 2. The construction works involved overall residential development and were not specific to the building such as site clearance works, external works, and infrastructure works were excluded.  The LCA modelling has been carried out in SimaPro V7.3.3 (PRé Consultants bv, Amersfoort, The Netherlands) [27]. SimaPro is one of the leading LCA software programs produced by PRé Consultants bv and used by LCA practitioners all over the world as a decision support tool [28]. The Malaysia Life Cycle Inventory Database (MYLCID) was used in the LCI, especially on raw materials such as cement and diesel, in order to produce significant results for the Malaysian scenario [29]. Due to data limitation, the Ecoinvent database was used and adapted to Malaysian conditions by replacing the local electricity mix data set as suggested by Horváth and Szalay [30]. The databases used in this study have considered the detail processes of each material in manufacturing, transportation, and disposal involved during its life cycle [29,31].

Pre-Use Phase
The LCI data for the pre-use phase were obtained from the bill of quantities. The quantities were then divided into GFA of the building as shown in Table 1. Few assumptions have been considered due to the limitation of the databases as follows: • An additional 5% of material waste during construction was added from the total amounts from the bill of quantities as suggested by previous studies [32,33].

•
In Malaysia, only steel and aluminium were recycled, whereas other materials are transported to the landfill as suggested by Arham [34]. The building materials related to steel and aluminium i.e., the reinforcement bars, aluminium window and door frames in the case studies were adjusted accordingly by replacing the use of pig iron and primary aluminium to scrap iron and old aluminium scrap, respectively, as suggested in the SimaPro.

•
The types and materials were limited to process data equipped in the databases. • Acrylic emulsion paint was substituted with alkyd paint due to the limitation in the databases.

•
The transportation distances from the manufacturer to the construction site were assumed to be 300 km for all materials; meanwhile, the distance is 50 km for a ready-mix concrete, as suggested by Wittstock et al. [35]. • A 16-ton lorry was used to transport materials from manufacturers to the site, whereas a 24-ton ready-mix lorry was used to transport concretes.

•
The transportation data were calculated based on impact per ton kilometre (tkm) fleet average from the Ecoinvent database with adaptation of Malaysian data from MYCLID for electricity and diesel. The CO 2 emissions for the 16-ton and 24-ton lorry were estimated at 0.84822 kg and 0.93854 kg per tkm, respectively [29,31].

Construction Phase
Only three construction processes were taken into consideration-namely, excavation, transportation of the excavator to the construction site, and temporary timber formwork. An excavator was used during excavation works. Meanwhile, other installation work was assumed to be completed by manual labours. The transportation of the excavator was considered to be a 50 km distance from the construction site using a 40-ton low-loader. The formwork was expected to be used multiple times before disposal as suggested by Abdullah [36].

Use Phase Operation Data
Total electricity consumption was estimated at about 2949.78 kWh·per·m 2 as shown in Table 2. Energy simulation software OpenStudio V1.2.0 (Alliance for Sustainable Energy, LLC, Lakewood, CO, USA) [37] with EnergyPlus was used to estimate the annual electricity consumption of air conditioning, illumination, and electrical equipment. The Kuala Lumpur weather data for the year 2013 was used as the basis. The air-conditioning system was set at 20.8 degrees Celsius from 10:00 p.m. to 6:00 a.m. every day in the master bedroom and two other bedrooms on the first floor based on findings by Kubota et al. [38]. The electricity consumption was assumed to be constant throughout the operation of the house. Maintenance Data Maintenance data was estimated based on the selected elements such as painting, replacement of roof coverings, and also changing of windows as suggested by other studies [39,40]. The replacement intervals were based on the report by National Association of Home Builders (NAHB) due to data limitations in Malaysia as suggested by Iyer-Raniga and Wong [26]. The replacement interval is shown in Table 3, which includes the production and transportation of the selected building materials. EOL phase was incorporated into the LCA studies because of the ability of recycling potential of building materials, which reduced the embodied energy [41]. As mentioned earlier in the pre-use phase, only steel and aluminium were recycled in Malaysia, thus these two materials were used as raw materials instead of aluminium and iron ores to reduce environmental impact as suggested in the SimaPro [27]. The transportation distances from the construction site to landfill and recycling centre were assumed to be 300 km from the construction site. The disposal of inert materials to the landfill with renaturation after closure and 50% of the sites feature a base seal and leachate collection system.

Life Cycle Impact Assessment (LCIA)
The midpoint assessment used the approach developed by Centre of Environmental Science (CML), Leiden University [42]. Only four common impact categories from CML 2001 were applied-namely, global warming potential (GWP), acidification, ozone depletion (ODP), and eutrophication as suggested by Khasreen et al. [43].

Interpretation
LCIA was interpreted according to the goal and scope of the study that shall include an assessment and a sensitivity check of the significant inputs and outputs [23]. The findings later will be validated by comparing it to other published studies [40]. Figure 3 shows the results of total LCIA. Operation phase of the building life cycle has the highest impact on GWP and acidification compared to other phases. This is due to the use of fossil fuel in the electricity generation mix in Malaysia. The pre-use phase has the highest impact on ODP compared to other phases mainly contributed by materials and processes in the production of the wall (6.28 × 10 −6 kg CFC-11 eq). The construction phase has the lowest overall environmental impact, which is similar to previous studies [32,40,41]. EOL has the highest impact in eutrophication compared to other phases with 1.92 kg PO 4 -eq, which were contributed by the disposal of clay bricks to landfill. The maintenance phase has a lower impact in comparison to the pre-use phase due to the low quantity of materials used.  Table 4 shows the environmental impact of every element in the pre-use phase. The substructure has the highest impact of acidification and eutrophication, and GWP largely contributed due to the substantial quantity of cement in concrete-based building elements, which account for 77%, 53%, 81%, respectively. Stairs have the lowest overall impact due to small quantities of material used per GFA.

Overview of the Results
During the maintenance phase, the painting and aluminium frame window have been identified as the two highest environmental impact contributors. Painting has the largest impact on acidification, eutrophication, and ODP due to higher replacement frequencies. Meanwhile, the aluminium frame window has the highest impact on GWP as shown in Table 5.
The environmental impact during the EOL phase has the highest level of eutrophication with a relatively high GWP. Figure 4 shows the LCIA of transportation to the landfill and disposal of building materials. The impact of clay brick disposal was the highest in all impact categories followed by cement based products.  Table 4 shows the environmental impact of every element in the pre-use phase. The substructure has the highest impact of acidification and eutrophication, and GWP largely contributed due to the substantial quantity of cement in concrete-based building elements, which account for 77%, 53%, 81%, respectively. Stairs have the lowest overall impact due to small quantities of material used per GFA.
During the maintenance phase, the painting and aluminium frame window have been identified as the two highest environmental impact contributors. Painting has the largest impact on acidification, eutrophication, and ODP due to higher replacement frequencies. Meanwhile, the aluminium frame window has the highest impact on GWP as shown in Table 5.
The environmental impact during the EOL phase has the highest level of eutrophication with a relatively high GWP. Figure 4 shows the LCIA of transportation to the landfill and disposal of building materials. The impact of clay brick disposal was the highest in all impact categories followed by cement based products.

Impact of Materials
Contribution analysis process has been carried out to identify materials or processes that produce the highest impact. In the pre-use phase, the substructure has been identified as the largest impact for acidification, eutrophication, and GWP. Concrete was found to be dominant in every impact category compared to steel reinforcement and hardcore as shown in Table 6. In the production of concrete, cement was identified as the highest contributor, followed by transportation of concrete to the site as shown in Table 7. This study however, did not consider the potential of CO2 uptake during accelerated concrete carbonation curing for carbon capture and storage, as the technology has not been adopted yet in Malaysia [44]. The environmental impact and emission of cement production in Malaysia were calculated based on the MYLCID, where the main processes in cement production consist of raw material extraction, production of clinker, and cement grinding [29]. The clinker cement is comprised of a mixture of primary products of mainly calcium oxide, silica, aluminium oxide, and iron oxide. Limestone, chalk, and clay provide these chemical constituents. The raw material mixture is heated to approximately 1450 °C in a rotary furnace until sintering, which leads on average to the production of 570 kg CO2/t of cement (plus combustion emissions). Other materials used in concrete production such as aggregate have a very minimal impact. The CO2 emissions of aggregate production for 1 m 3 of concrete mixture used in the building were 2.34 kg compared to 359 kg for cement.

Impact of Materials
Contribution analysis process has been carried out to identify materials or processes that produce the highest impact. In the pre-use phase, the substructure has been identified as the largest impact for acidification, eutrophication, and GWP. Concrete was found to be dominant in every impact category compared to steel reinforcement and hardcore as shown in Table 6. In the production of concrete, cement was identified as the highest contributor, followed by transportation of concrete to the site as shown in Table 7. This study however, did not consider the potential of CO 2 uptake during accelerated concrete carbonation curing for carbon capture and storage, as the technology has not been adopted yet in Malaysia [44]. The environmental impact and emission of cement production in Malaysia were calculated based on the MYLCID, where the main processes in cement production consist of raw material extraction, production of clinker, and cement grinding [29]. The clinker cement is comprised of a mixture of primary products of mainly calcium oxide, silica, aluminium oxide, and iron oxide. Limestone, chalk, and clay provide these chemical constituents. The raw material mixture is heated to approximately 1450 • C in a rotary furnace until sintering, which leads on average to the production of 570 kg CO 2 /t of cement (plus combustion emissions). Other materials used in concrete production such as aggregate have a very minimal impact. The CO 2 emissions of aggregate production for 1 m 3 of concrete mixture used in the building were 2.34 kg compared to 359 kg for cement.  In comparison to other building elements, the wall contributed the highest ODP mainly from transportation of natural gas with 3.24 × 10 −6 kg CFC-11 eq (54%) and crude oil production with 2.47 × 10 −6 kg CFC-11 eq (41%).

Sensitivity Analysis
Other researchers suggested that uncertainties in the method of measurement and geographical representative would influence the results [39,45]. This step was conducted to determine the influence of the uncertainties in the assumptions in this study specifically on the transportation distances and the impact of electricity production in different locations. For transportation, the predetermined distances were 50 km for concrete and 300 km for other materials. The standard deviation of ±20% is allocated for transportation distance as suggested by Wen et al. [21]. A substructure element was used as the base case scenario, as it has the largest impact. Results show that the transportation distances have minimal impact overall with the highest changes of 8.78% in ODP, while other impact categories had below 6% variance, as shown in Table 8. Table 8. LCIA with ±20% standard deviation for transportation distance for substructure.

Impact Category Unit Percentage
Acidification kg SO 2 eq 3.06% Eutrophication kg PO 4 eq 5.51% Global warming (GWP100) kg CO 2 eq 2.54% Ozone layer depletion (ODP) kg CFC-11 eq 8.78% Similar to previous findings, energy consumptions were identified as the largest impact on the environment. The Malaysian electricity generation mix is different to other countries because the major source of production is fossil fuel. The power stations in Malaysia consist of gas-fired, coal-fired, gas and coal-fired, oil-fired and hydro, but natural gas is the highest main fuel source [29]. Electricity generated by fossil fuels contribute to high greenhouse gas (GHG), which then leads to global warming. Figure 5 shows the midpoint environmental impact of 1 kWh electricity generation in Malaysia, Great Britain, Spain, Germany, and France by using CML 2001. Malaysia has the highest impact on GWP, the third highest in acidification and the lowest in ODP. Malaysia acidification impact is the third overall, but it has the largest emission of nitrogen oxides compared to other countries. The GWP impact in Malaysia is marginally higher (8.19 × 10 1 kg CO 2 eq) due to the release of carbon dioxide from fossil fuels. The different electricity generation mix in the various countries will produce different environmental impact. Thus, the findings for this study are limited to Malaysia.

Comparison with Other Studies
Data validation is part of the LCA process as suggested in ISO 14044 and can be done by comparing the results to other published research [23, 40,46]. Since no cradle-to-grave LCA studies for Malaysian residential buildings are available, the results were compared to a conventional fourstorey flat and an IBS four-storey flat located in Johor, Malaysia from cradle-to-gate, i.e., from preuse to construction only. Subsequently, cradle-to-grave comparison was made to the building in Spain and UK on the impact of GWP, acidification, and ODP since the type of building and the LCA method used in the studies were fairly similar. However, for the building in the UK, only GWP was considered as other impacts were not available. The comparison of selected impact categories with other studies is shown in Figure 6 and Table 9.

Comparison with Other Studies
Data validation is part of the LCA process as suggested in ISO 14044 and can be done by comparing the results to other published research [23, 40,46]. Since no cradle-to-grave LCA studies for Malaysian residential buildings are available, the results were compared to a conventional four-storey flat and an IBS four-storey flat located in Johor, Malaysia from cradle-to-gate, i.e., from pre-use to construction only. Subsequently, cradle-to-grave comparison was made to the building in Spain and UK on the impact of GWP, acidification, and ODP since the type of building and the LCA method used in the studies were fairly similar. However, for the building in the UK, only GWP was considered as other impacts were not available. The comparison of selected impact categories with other studies is shown in Figure 6 and Table 9.

Comparison with Other Studies
Data validation is part of the LCA process as suggested in ISO 14044 and can be done by comparing the results to other published research [23, 40,46]. Since no cradle-to-grave LCA studies for Malaysian residential buildings are available, the results were compared to a conventional fourstorey flat and an IBS four-storey flat located in Johor, Malaysia from cradle-to-gate, i.e., from preuse to construction only. Subsequently, cradle-to-grave comparison was made to the building in Spain and UK on the impact of GWP, acidification, and ODP since the type of building and the LCA method used in the studies were fairly similar. However, for the building in the UK, only GWP was considered as other impacts were not available. The comparison of selected impact categories with other studies is shown in Figure 6 and Table 9.  The GWP of this study was 8.28 × 10 2 kg CO 2 eq, while the flats were much lower at 3.44 × 10 2 kg CO 2 eq and 2.98 × 10 2 kg CO 2 eq. In flats, the ratio of certain elements such as roofs, walls, floors and ceilings were shared between multiple units, which reduced the impact per m 2 GFA. The specification and the quantity per m 2 also contributed to the difference. For example, detailed specifications of the brick used in the 4-storey flats were not clearly mentioned. In general, low to medium cost houses use cheaper cement-based brick, which has lower energy used in production in comparison to clay bricks, and thus will influence the overall GWP [47]. The comparison of GWP impact category for cradle-to-grave between three semi-detached houses is relatively comparable. Since the larger share of GWP is from the use phase, the method used in determining the energy consumptions, climates, and impact from electricity generation mix in different countries contributed to variations in results. The energy consumption for the house in Spain was estimated using DesignBuilder software (DesignBuilder Software Ltd., London, UK) while data from statistics and estimation were used for the house in the UK. The air-conditioning system uses a large share of energy in the case study (47%) and 26% in the semi-detached house in Spain. However, the majority of the energy usage in the semi-detached house in the UK was contributed by space heating (59%), which was not applicable to the case study in Malaysia because of the hot and humid weather. Acidification results for the case study and the house in Spain were also primarily contributed by the use phase. However, the ODP for this study was lower in comparison to other buildings. The ODP in the case study was largely contributed by the pre-use phase rather than the use phase in Spain, which contributed to higher ODP levels per kWh of electricity used.

Conclusions
LCA is a crucial tool in measuring detailed environmental impact, especially towards the building industry. This study has assessed the environmental impacts of a conventional residential building in Malaysia from cradle-to-grave, i.e., during pre-use, construction, use, and EOL using four impact categories from CML 2001-namely, GWP, acidification, ODP, and eutrophication. The limitation of this study was based on the LCA method and assumptions in the goal and scope definition, LCI, LCIA, and interpretation. It was found that the building operation during the use phase produced the highest GWP (2.14 × 10 3 kg CO 2 eq) and acidification (1.10 × 10 1 kg SO 2 eq) compared to other phases during the building life cycle. In the pre-use phase, concrete in the substructure has been identified as the largest contributor to GWP (3.65 × 10 2 kg CO 2 eq), acidification (1.54 kg SO 2 eq), and eutrophication (2.22 × 10 −1 kg PO 4 eq) with cement as the primary raw material. In the maintenance phase, painting has the highest impact on acidification (2.13 × 10 −1 kg SO 2 eq), eutrophication (7.52 × 10 −2 kg PO 4 eq) and ODP (4.81 × 10 −6 kg CFC-11 eq), while the aluminium window frame has the highest impact on GWP (4.21 × 10 1 kg CO 2 eq). In EOL, clay bricks and concrete contributed to major environmental impacts. The results of this study showed that residential building in Malaysia is comparable to the building in Spain and UK. The study also showed that uncertainties in the method of measurement, data quality, and different geographic location would influence the results. The findings in this study are useful to government agencies and building professionals on the environmental impacts of building construction, especially in Malaysia as well as other countries with similar conditions.