3.1 LCA Results of Single-Family House
The LCA results of a single-family house in Turkey by considering cradle-to-grave approach were calculated using ReCiPe midpoint (H) method and the results were indicated in Table 1. LCA analysis consists of six environmental impact categories (GWP, ODP, AP, EP, HTP and LU) to reveal the environmental performance of the buildings. The value of GWP was calculated as 3.26E+03 kg CO2 eq for the single-family house given in Table 1. The main contributor factor for GWP were fossil-based energy consumption for lighting, HVAC, running appliance and maintaining the comfort conditions regularly in the operation phase. Besides, the value of ODP for the single-family house was 6.76E+00 kg NOx eq (Table 1). The usage of vinyl-based materials particularly in window frames for residential buildings and use of CFCs and HCFCs in manufacturing of insulation materials are the main reasons of the ODP impact category (Azari 2014).
Table 1
Impact category values of single-family house per m2 of floor area (ReCiPe midpoint (H) method)
Impact category | Unit | Single-Family House |
Global warming potential | kg CO2 eq | 3.26E+03 |
Ozone layer depletion | kg NOx eq | 6.76E+00 |
Acidification potential | kg SO2 eq | 3.21E+01 |
Eutrophication potential | kg P eq | 2.94E+00 |
Human toxicity potential | kg 1,4-DBC e | 2.39E+02 |
Land use | m2a crop eq | 6.11E+01 |
In this study, process-based analysis is used for evaluation of environmental impacts of single-family house. Within the entire life cycle, processes are mainly divided into three categories, which are pre-operation, operation and post-operation phases. In pre-operation phase, extraction of raw materials, transportation of materials and construction of single-family house are included in system boundaries. The operation phase consists of operation, maintenance and replacement of the building for service life of 50 years. In operation phase, consumption electricity, natural gas and water, generation of solid waste and wastewater are taken into account for single-family house. Lastly, post-operation phase covers the demolition of single-family house at the end of its life. The operation phase is dominant on the distribution of GWP for single-family house with 79% and pre-operation follows with 20% contribution as shown in Fig. 3. These LCA results are comparable with published LCA findings in the literature. For instance, Dara et. al. (2019) performed a LCA study for single-family house in Canada with cradle-to-gate approach. They report that use and operation phase accounts for 85-95%, of the total life cycle impact (Dara et al. 2019). Petrovic et. al. (2019) applied a LCA on a wooden single-family house in Sweden within the life span of 100 years by considering entire life cycle stages. They revealed that in-use stage has highest environmental impact (64%) and then production and construction stage follows with 30% and 4%, respectively (Petrovic et al. 2019). Zhang et. al. (2013) studied on LCA of a two-storey single-family house in Vancouver, Canada over 60 years lifespan. Their findings revealed that the major contributor phase is operation with 30-90% while manufacturing is about 7-51% and end-of-life accounted less than 1% impact (Zhang et al. 2014). Atmaca (2017) studied on LCA of post-disaster temporary housing to estimate the total energy use and CO2 emissions and he showed that operation phase is dominant in CO2 emissions of both container houses and prefabricated houses with 96% and 95% contribution, respectively (Atmaca 2017).
The distribution of GWP by sub-components of single-family house for operation phase, which is the most dominant phase, is indicated in Fig. 4. In operation phase, electricity made up 87% of the total GWP for the single-family for GWP were fossil-based electricity consumption for lighting, HVAC (heating, ventilation, and air conditioning), running appliance and maintaining the comfort conditions regularly in the operation phase. These obtained results are similar with the literature on the life cycle assessment of single-family houses. Petrovic et. al. (2019) studied on LCA of a wooden single-family house in Sweden within the life span of 100 years and it was found that operational energy use has 64% share due to high electricity consumption and maintenance phase follows with 16% share of the total (Petrovic et al. 2019). In Turkey, residential buildings are responsible for approximately 32% of the total energy demand, after industry sector with 40% (Atmaca 2016). It is also stated that final electricity consumption per capita increased from 1404 kWh to 2493 kWh between 2001 and 2011 in Turkey. Regarding to this issue, residential buildings have major potential to decrease energy consumption and greenhouse gas emissions (Stephan et al. 2012). Therefore, the building industry must strive to use renewable energy sources in order to reduce their environmental impacts with a sustainable approach.
The distribution of GWP by sub-components of single-family house for pre-operation phase is shown in Fig. 5. In pre-operation phase, most of the GWP is contributed from steel (34%), concrete (29%), transportation (17%), bricks (6%) and the remaining are the other raw materials used for the construction of buildings. Steel is one of the widely used construction materials due to its well mechanical and physical properties. According to World Steel Association, nearly 50% of the produced steel worldwide is used in construction buildings and infrastructure (WorldSteelAssociation 2008). However, manufacturing of steel has significant environmental impacts like greenhouse gas emissions to the atmosphere. International Energy Agency reports that global steel production is responsible for 9% of the global carbon dioxide emissions (IEA 2008). Concrete is another mostly used construction materials due to its strength and durability. After water, concrete is the second most consumed material worldwide (Gagg 2014).
The obtained LCA results are also coherent with the literature on LCA of construction materials for various purposes. Evangelista et. al. (2018) applied an environmental performance analysis for residential buildings using LCA in Brazil. Their results showed that steel and concrete had the largest environmental impacts in almost all categories with contribution ranging from 44–61% because of their structure’s high concentration (Evangelista et al. 2018). Monahan and Powell (2011) studied on an embodied carbon and energy analysis of construction methods by using life cycle assessment approach. They revealed that concrete is the major contributor with 36% of the embodied carbon among the used construction materials (Monahan &Powell 2011). Atmaca (2017) studied on LCA of post-disaster temporary housing to estimate the total energy use and CO2 emissions and he showed that steel and concrete are main contributors of CO2 emissions in construction phase. He revealed that share of steel varies from 38–42% and share of concrete varies from 9–19% as dominant factors in construction phase (Atmaca 2017).
3.2 Lca Results Of Multi-storey Apartment
The environmental impacts of a multi-storey apartment building in Turkey by considering cradle-to-grave approach were calculated using ReCiPe midpoint (H) method and the results were indicated in Table 2. LCA analysis consists of six environmental impact categories (GWP, ODP, AP, EP, HTP and LU) to reveal the environmental performance of the buildings. The value of GWP was calculated as 2.28E+03 kg CO2 eq for the multi-storey apartment building given in Table 2. The main contributor factor for GWP were fossil-based energy consumption for lighting, HVAC, running appliance and maintaining the comfort conditions regularly in the operation phase. Therefore, the building industry must strive to use renewable energy sources in order to reduce their environmental impacts with a sustainable approach. Besides, the value of ODP and LU was 5.05E+00 kg NOX eq and 5.80E+01 m2a crop for the multi-storey apartment building, respectively (Table 2).
Table 2
Impact category values of multi-storey apartment per m2 of floor area (ReCiPe midpoint (H) method)
Impact category
|
Unit
|
Multi-Storey Apartment
|
Global warming potential
|
kg CO2 eq
|
2.28E+03
|
Ozone layer depletion
|
kg NOx eq
|
5.05E+00
|
Acidification potential
|
kg SO2 eq
|
2.45E+01
|
Eutrophication potential
|
kg P eq
|
2.90E+00
|
Human toxicity potential
|
kg 1,4-DBC e
|
2.12E+02
|
Land use
|
m2a crop eq
|
5.80E+01
|
The process-based analysis is used for evaluation of environmental impacts of multi-storey apartment in this study. The processes are divided into three main categories, which are pre-operation, operation and post-operation phases. The pre-operation phase covers raw material extraction, transportation of materials and construction of building while operation phase consists of operation, maintenance and replacement and post operation refers to demolition of the building. The operation phase is dominant on the distribution of GWP for single-family house with 78%, pre-operation and post-operation follow with 20% and 1% contribution as shown in Fig. 6. These LCA results can be compared with published LCA findings in the literature. Mehta et. al. (2017) applied a life cycle energy assessment of a multi-storey residential building and they showed that the operational energy refers to energy used for heating, cooling, ventilation and electrical appliance account for 84% of the total life cycle energy with 50 years of service life (Mehta et al. 2017). Asdrubali et. al. (2013) studied on LCA of three conventional Italian buildings and they found that operation phase has largest contribution with 77-85% to the total impact. They also showed that share of construction phase on total impact varies from 14–21% as second most contributor phase (Asdrubali et al. 2013).
The distribution of GWP by sub-components of multi-storey apartment for operation phase, which is most dominant phase, is indicated in Fig. 7. In operation phase, electricity accounts for 83% of the total GWP for the single-family for GWP were fossil-based electricity consumption for lighting, HVAC, running appliance and maintaining the comfort conditions regularly in the operation phase. These obtained results are similar with the literature on the life cycle assessment of multi-storey apartment. In a study, LCA of three conventional Italian buildings was performed and it is found that the impact of the electricity consumption ranges from 43–74% for operation phase mostly due to coal-based power contribution in the electricity grid (Asdrubali et al. 2013). Regarding to this issue, residential buildings have major potential to decrease energy consumption and greenhouse gas emissions (Stephan et al. 2012). Therefore, the building industry must strive to use renewable energy sources in order to reduce their environmental impacts with a sustainable approach.
The distribution of GWP by sub-components of multi-storey apartment for pre-operation phase is shown in Fig. 8. In pre-operation phase, most of the GWP is contributed from steel (40%), concrete (28%), transportation (9%), cables (7%) and the remaining are the other raw materials used for the construction of buildings. These LCA results are also coherent with the literature on LCA of construction materials for various purposes. Lu et. al (2017) performed a study to compare alternative materials for Australian multi-storey apartment building from environmental and economic perspective. Their results revealed that wooden houses have greater performance than concrete and steel houses in terms of embodied energy and GWP. They also showed that steel and concrete had the largest environmental burden in all impact categories in construction phase (Lu et al. 2017). In a study, a life cycle energy assessment was applied on a multi-storey residential building and they showed that steel (39.2%), cement (17.9%), aluminum (13.8%) and concrete (9.2%) are the major contributors of the life cycle energy in construction phase (Mehta et al. 2017). Monahan and Powell (2011) studied on an embodied carbon and energy analysis of construction methods by using life cycle assessment approach. They revealed that concrete is the major contributor with 36% of the embodied carbon among the used construction materials (Monahan and Powell 2011).
3.3 Comparison Of Lca Result Of The Two Buildings
The comparison of the total environmental impact of the two case studies (single-family house and multi-storey apartment building) is illustrated in Fig. 9. The single-family house shows higher impact when compared with the multi-storey apartment for all impact categories (GWP, ODP, AP, EP, HTP, and LU) primarily because its total gross area is smaller than the multi-storey apartment. Taking this building as a reference (100%), a relative comparison of its impact categories and those of the other case study was analyzed (Fig. 9). Although the total mass value of materials increased for multi-storey apartment, the greater gross living area still reduce the final contribution of total environmental impacts per unit area. For GWP, the multi-storey apartment presented the lowest environmental impact (70%) due to its larger area, average population and fossil-based energy consumption profile compared with the single-family house. The second highest difference between the two building types considered was obtained for the ODP impact category. For ODP, the multi-storey apartment performed 25% lower impact than the single-family house due to its larger gross area, the higher contribution of insulating materials (e.g., glazed windows, vinyl, etc.) over the pre-operation and operation phases and the greater mass value of walls and windows per unit area.
The distribution of overall LCA results over 50 years lifespan by life cycle phases is shown in Table 3. The LCA results of the two case studies indicated that the majority of the environmental impacts occur at the operation phase (31-91%), followed by the pre-operation (9-67%). The post-operation phase has a negligible impact (less than 2%). These LCA results can be compared with published LCA findings in the literature. For instance, Dara et. al. (2019) performed a LCA study for single-family house in Canada with cradle-to-gate approach. They reported that use and operation phase accounts for 85-95%, of the total life cycle impact (Dara et al. 2019). Petrovic et. al. (2019) applied a LCA on a wooden single-family house in Sweden within the life span of 100 years by considering entire life cycle stages. They revealed that in-use stage has highest environmental impact (64%) and then production and construction stage follows with 30% and 4%, respectively (Petrovic et al. 2019). Zhang et. al. (2013) studied on LCA of a two-storey single-family house in Vancouver, Canada over 60 years lifespan. Their findings revealed that the major contributor phase is operation with 30-90% while manufacturing is about 7-51% and end-of-life accounted less than 1% impact (Zhang et al. 2014). Evangelista et. al. (2018) performed environmental impact analysis for residential buildings in Brazil with LCA tool. They calculated the environmental performance of four Brazilian residential buildings with various typologies with cradle-to-grave approach. Their analysis results showed that operation stage has highest environmental impact varies between 35% and 93% of the total impact. In addition, they revealed that pre-operation stage (6-64%) is the second main contributor stage and post-operation stage (0-6%) has lowest impact on environmental performance of the residential buildings (Evangelista et al. 2018). Additionally, an LCA of three conventional Italian buildings (a detached house, a multi-dwelling residential building, and an office building) was studied and it is found that operation phase has largest contribution with 77-85% to the total impact. They also showed that share of construction phase on total impact varies from 14–21% as second most contributor phase (Asdrubali et al. 2013).
Table 3
Distribution of impact categories by life cycle phase
Impact Categories | Multi-Storey Building (%) | Single-Family House (%) |
| Pre Op. | Op. | Post Op. | Pre Op. | Op. | Post Op. |
Global warming potential | 21 | 78 | 1 | 20 | 79 | 1 |
Ozone layer depletion | 27 | 72 | 1 | 26 | 73 | 1 |
Acidification potential | 13 | 87 | 0 | 9 | 91 | 0 |
Eutrophication potential | 17 | 83 | 0 | 9 | 91 | 0 |
Human toxicity potential | 43 | 57 | 0 | 40 | 60 | 0 |
Land use | 58 | 41 | 1 | 67 | 31 | 2 |
Pre Op. = Pre-operation; Op.= Operation; Post Op.=Post-operation |