Variants of determining the construction production carbon footprint

The aim of the paper is to quantify the construction production carbon footprint per m3 of the built-up volume of the building. In order to determine the carbon footprint, 5 typical detached houses were selected. The individual buildings have the same material-construction characteristics; however, they differ in the size of the built-up volume, i.e. also in the built-up area. The LCA software was used to quantify the carbon footprint during the production phase of the model houses project. A budget indicator per m3 of the built-up volume was determined based on these calculations.


Introduction
Recently, men have stopped behaving in harmony with nature and have started to transform it in a very significant way.The intensive exploitation of natural resources disturbs the Earth's balance, leading to many environmental problems at the global level.The air, water and soil are being burdened by emissions of pollutants having a negative impact on both the environment and human health as a result of construction production.Climate change represents the most important environmental as well as political and economic issues of the 21 st century [1][2][3].The Paris Agreement which aims to reduce greenhouse gas emissions so that the temperature increase does not exceed 1.5 °C and thus keep global warming at an acceptable level, was adopted at the Paris Climate Conference United Nations Summit in 2015 [4,5].The Agreement included all major emitters of greenhouse gases and it replaced the Kyoto Protocol in 2016 [6][7][8].
The UN Environment Programme (UNEP) develops an annual Emissions Gap Report, which aims to achieve agreed goals at the lowest possible cost.Emissions from all greenhouse gases are expected to be reduced and 42 GtCO 2e (Global total CO 2 emissions) should not be exceeded in 2030 [9].The latest assessment shows that the EU is well on track to exceed the current target, mainly thanks to the progress in the use of renewable energy sources across Europe [10].The transition to a climate-neutral economy will only be possible if everyone contributes to it.The key to achieving climate neutrality is to reduce energy supplies [11,12].The construction industry consumes approximately 40 % of the world's annual energy consumption [13].It is energy consumption that contributes significantly to the global warming of the Earth [14].As a result, the first passive houses began to be built in Germany in the 1990s to reduce this consumption, where architects were able to reduce operating energy consumption ten times compared to low-energy houses [15][16][17].Currently, it is necessary to promote architecture that, in addition to meeting the needs, addresses the issue of protection and prevention of negative impacts on nature within the whole process from the construction, through the use to the demolition of the building and its subsequent recycling [18].The term sustainable architecture means preserving the environment for future generations.It does not deal just with saving energy, using healthy materials from renewable sources [19,20], but addresses all contexts such as the protection of cultural values, managing the development of large settlements to work well and efficiently and does not leave a large ecological footprint [21].The amount of the human activity impact on the environment (especially on climate change) is referred to as the carbon footprint [22].It is a measure of the amount of greenhouse gas emissions arising from certain activities or products [23].Results are given in CO 2 equivalents [24].The amount of carbon footprint can be determined at national, city, individual, company or product levels.The most important greenhouse gas is clearly carbon dioxide, which chemical formula is CO 2 and it is released during burning fossil fuels, such as crude oil, natural gas, coal, etc [25,26].
Currently, the construction industry makes an effort to mitigate its negative impact on the environment [27].The construction industry is one of the largest global consumers of natural resources [23].It significantly contributes to the production of greenhouse gases both from the construction itself, the subsequent building operation and finally its liquidation [28].Therefore, the assessment of buildings and their environmental certification has been introduced.There are many possibilities and ways to reduce CO 2 emissions during the building life cycle, i.e. from the implementation phase, through the operational phase to the liquidation phase [29].Construction work represents a complex of a large number of products and works with a long service life, where the operational phase forms a major part of the building life cycle.The design itself can take into account the bound emissions of materials and their service life [30,31].The aim of the research described in this article is to determine the carbon footprint per production unit of the budget indicator, mainly in the phase of production of building materials and in the implementation phase of the building.The calculation of the carbon footprint mainly takes into account the impact of the life cycle of the material used for the construction.

Methodology
Global warming refers to the phenomenon of a long-term increase in the average surface temperature of the Earth, which leads to further climate change such as ice melting, sea levels rising, precipitation changes, more frequent extreme weather conditions such as drought, floods and others [32,33].Global warming is caused by increasing concentrations of greenhouse gases in the atmosphere, which amplify the greenhouse effect [34,35].The global warming potential indicates how much heat the greenhouse gas traps in the atmosphere [36].It is calculated in carbon dioxide equivalents and is determined in units of kg CO 2 eq.CO 2e emissions (GWP -Global Warming Potential) and includes emissions of substances [37,38].The equivalent means that these are not only carbon dioxide emissions, but also other greenhouse gas emissions (methane, nitrous oxide, sulphur hexafluoride, freons and halons) [39].Their production is perceived as a carbon footprint [40].The carbon footprint is thus a measure of the human activity impact on the environment and it is an indirect indicator of the consumption of energy, products and services [41,42].Various specialized software and inventory data databases are used to calculate and model product life cycles [43].The professional One Click LCA software, developed by the Bionova company, was used in this research.One Click LCA software provides various data sources from around the world [44].For the purposes of the calculations, the vast majority of the data was taken from the Cenia and Ökobau.datdatabases, thanks to the largest available coverage of materials commonly used in Central Europe.This LCA software covers the life cycle stages from the cradle to the grave.It distinguishes product phases, construction process, use phase, operational energy and end of the life cycle Variants of determining the construction production carbon footprint phase [45].The LCA system was chosen to calculate the carbon footprint, while the software itself provides further assessments, such as the BREAMM Mat or the CML Life Cycle Cost [46].The One Click LCA software used allows data to be displayed according to the items, groups and subgroups of materials that contribute most to a certain impact category.It allows assessing both the share of individual materials or structural elements and the overall environmental impact of the project.The software provides various environmental impact indicators: Global Warming Potential (kg CO 2 e), Acidification Potential (kg SO 2 e), Eutrophication Potential (kg PO 4 e), Ozone Depletion Potential (kg CFC-11e), Photochemical Ozone Creation Potential (kg Ethene), total Primary Energy use (MJ), Abiotic Depletion Potential (kg Sb e), and others.Although all the listed impact indicators are essential for the life cycle assessment, this article takes into account especially the carbon footprint of buildings, i.e. the Global Warming Potential, which is given in units of kg CO 2 or t CO 2 [41].The purpose of the research described in the article was to determine the average amount of the carbon footprint per unit of the budget indicator [47].The determination of the carbon footprint per unit of production of the budget indicator may be related to the unit of the built-up volume or the built-up area of individual buildings.The Czech national classification: the Uniform Classification of Buildings and Construction Work of a Production Nature (JKSO) was therefore chosen to determine the amount of the carbon footprint [48,49].This classification classifies buildings according to their technical properties and material characteristics in contrast to the International Classification of Types of Construction (CC) which classifies construction production according to the way of use [50].

Results and discussion
One Click LCA software divides the cycle into several phases, see Figure 1, according to the LEED methodology, which defines the stages of the life cycle (A1-A3, A4, B1-B5 and C1-C4), i.e. "Cradle to Grave".The "Cradle to Grave" model, therefore, covers processes from raw material extraction through material production, transport, inbuilding, maintenance during its lifetime to disposal.The software determines potential loads also beyond the system; however, it does not include these benefits and loads in the calculation results.The One Click LCA building life cycle assessment tool includes all the above-mentioned processes and impacts in the calculations.In order to determine the carbon footprint per unit of production of the budget indicator, it is necessary to determine the first two phases, i.e. the product phase (A1-A3) and the construction phase (A4-A5), as these two phases are the most accurate for the purpose of this research.The consumption of energy and water, which has the greatest impact on global warming, depends, for example, on the type of heating of the building, so these phases are not accurate enough for evaluating the total carbon footprint.An item budget, technical report and building design are required to determine the amount of material to create the carbon footprint of the building.Five sample detached houses were selected to determine the carbon footprint and the impact of construction production on the environment.All these sample houses were detached, without a basement, based on concrete foundation strips, the load-bearing system was made of brick, with a timber roof framework and tile roof covering.These houses were selected to correspond to the JKSO classification in the chapter Houses for a living -single-family houses; isolated; masonry of bricks or blocks; new building -803 61 11.First, it was necessary to assign the individual materials to determine the carbon footprint.Either the exact product from the manufacturer was looked up or the closest match was found.If necessary, it is possible to use general data in case a suitable product cannot be found, therefore a product with similar quality can be used instead.These general materials can be found mainly in the German database Öekobau.dat.However, each material has its own service life, which is needed to calculate the impacts resulting from its replacement and disposal in category B4-B5.A default initial service life that is automatically applied to each material can be set In One Click LCA program.If necessary, this value can be set manually in the settings, however, this option was not used in the research.The same applies to the transport distance of the material.The transport mode and the distance from the building material manufacturer to the construction site are used for each material in the assessed building.Distances are automatically Zdenek Krejza, Gabriela Kocourkova, Lucie Vankova, Michaela Sebestova defined using a compensation factor.As the assessed buildings are located in the Czech Republic, a local compensation factor that adjusts the impacts of material production to the conditions of the selected country was chosen.Therefore, by default, the software determines the localization of the material, which remains the same for all other objects to avoid confusion.The annual energy consumption of each house was determined based on the energy performance certificate of the building.The source of electricity was determined as Electricity, Czech Republic according to the programme of the Bionova EN15804 standard.The Global Warming Potential was 0.59 kg CO 2 e/kWh.Furthermore, Table 1 shows the values of annual energy consumption in MWh/year for individual assessed houses.This data was taken from energy certificates, which were provided together with the project documentation of the buildings.The indicator, set per production unit, can be used for the purpose of quick and easy determining the approximate amount of the carbon footprint.The basic principle is to determine the number of technical units, e.g. per m 3 of built-up volume or m 2 of built-up area.Sample detached houses were selected in order to determine the carbon footprint per unit of measure.Individual buildings differ in built-up volume, i.e. also in the built-up area.However, no extreme values that would have to be ruled out due to skewing of the results, appeared.
The following tables and figures quantify the environmental impacts during the entire life cycle of each evaluated detached house.The largest share of the carbon footprint is borne by energy consumption, followed by construction materials.However, only the first two phases are used to calculate the carbon footprint per unit of production of the budget indicator.The product phase, which includes the extraction of raw materials, transport and the actual production of materials, and the construction phase, which includes transport to the construction site and their inbuilt.The research aimed to determine the carbon footprint per the production unit of the budget indicator.shows the phases that were selected to determine the carbon footprint per production unit (construction material, transport and its inbuilt).
All building materials that were used to build the house were budgeted out.Table 3 shows a list of the imported materials for the House No.3.Similarly, lists of imported materials were prepared for the other assessed houses.It can be seen from Figure 2 above and the Table 4 that House No. 2 reaches the largest carbon footprint, 120.3 tons of CO 2 .It is the largest building in terms of the built-up volume or the built-up area.This is related to the largest amount of the built-in material.
Focusing on the resulting Table 5, this size of the building does not have a significant impact on the determination of the result, therefore this object could also be included in the calculation.Construction materials seem not to have the most significant impact on the carbon footprint creation as can be seen in Table 3 above and Figure 3. Their inbuilt follows, while the lowest carbon creation has their transport.As mentioned above, the largest producer of the carbon footprint is House No. 2 with 120.27 tons of CO 2 .In contrast, the lowest producer is House No. 1 with 51.98 t CO 2 .The Table 5 shows the determination of the carbon footprint per unit of production of the budget indicator.The built-up volume and the built-up area of individual buildings are calculated as well as their carbon footprint of phases A1-A5 of building life cycles and Zdenek Krejza, Gabriela Kocourkova, Lucie Vankova, Michaela Sebestova the production indicators were determined.The determination of the carbon footprint per unit of production of the budget indicator can be related to the unit of the built-up volume or the built-up area of individual buildings.The authors of the article assume that it is more accurate to determine the carbon footprint per m 3 of the built-up volume.This can be proven in Table 4, where the weighted arithmetic average of the built-up volume of 122.25 kg CO 2 /m 3 , the weighted arithmetic average of the built-up area of 608.60 kg CO 2 / m 2 and the carbon footprint of individual houses were determined.The row of the table "Difference from the average" gives evidence that the determination of the carbon footprint per production unit of the built-up space of buildings is more accurate.The carbon footprint has been currently quite high, so there is a tendency to reduce it.One of the possible recommendations to reduce the carbon footprint at the product phase is mainly to use local materials and raw materials so as to reduce the transportation distance of raw materials for the material production.Another option to reduce the carbon footprint at the construction phase is to use materials that have a lower carbon footprint in the production while maintaining the same, if not better, technical and physical properties [51].Secondly, to increase the application of circular economy principles.Thirdly, to motivate manufacturers to change or adapt technological processes in the material production.

Conclusion
The aim of the research described in the article was to determine the carbon footprint of construction production per the production unit of the budget indicator and to compare buildings of different production technology.There has been a strong emphasis on the environment in recent years while the construction industry has made a significant contribution to global warming.Therefore, this research focuses on the possible facilitation of the carbon footprint of buildings determination.The environmental impacts of the building operation are mainly influenced by their energy intensity e.g.efficiency.The greater the building energy consumption, the greater the environmental impacts.It is possible to reduce the energy intensity of buildings by making the heating sources greener using the Czech national subsidy New Green Savings Programme.Households can obtain subsidies for the replacement of a boiler, e.g. for a heat pump, a biomass boiler or a gas condensing boiler.Furthermore, the programme supports the construction of new buildings with very low energy intensity.
Five detached houses of the same production technology were selected for the purposes of the research described in the article, their built-up volume was calculated and the carbon footprint was determined using the One Click LCA software.Subsequently, the amount of the carbon footprint per 1 m 3 of the built-up volume (122.25 kg CO 2 /m 3 ) was determined using the weighted arithmetic average.The quantification of the carbon footprint took place during the production phase of the building, thus, in the phase which involves the extraction of raw materials, their transport and production, and in the construction phase, which includes transport to the construction site and subsequent inbuilding of the material.
Annual water consumption was considered the same for all types of houses.A model of the family of 4 living in the house was considered.Average water consumption per year according to Decree No. 120/2011 Coll. is 35 m 3 per inhabitant of the house, 1 m 3 is added for the consumption associated with the cleaning of the house surroundings.The annual water consumption per capita is 36 m 3 , for a family of 4, it was 144 m 3 per year.One Click LCA software makes it possible to add impacts related to the building site operation using project-specific data or use average impacts by climate zone.For the purpose of this research, the construction site scenario corresponding to the averages of our climate zone -temperate continental climate, was used.A suitable climatic zone and built-up area of the building in m 2 were selected.The averages include the average electricity, fuel consumption and waste production impacts on individual climatic zones.The expected average construction waste production for the temperate continental climate zone was 5 kg/m 2 , the expected electricity consumption was 37 kWh/m 2 and the expected total use of diesel oil was 4.5 l/m 2 .The Global Warming Potential (A1-A3) was 30.34 kg CO 2 e/m 2[29].The calculation period defines the lifespan of the building with all impacts calculated for this period.The program allows values between 0 and 80 years.Even though the lifespan of a brick house is approximately 100 years, the lifespan in the research was set at 50 years.It thus fell within the permitted values of the program.Product and construction phases, which are not affected by the service life of the entire building, were also required for the purpose of the research.It was necessary to determine carbon footprint in kg of CO 2 and built-up volume, or built-up area for individual buildings.The share of the carbon footprint and the built-up volume or built-up area determined a new indicator, in units of measure kg CO 2 /m 3 , or CO 2 /m 2 .This indicator could help to determine in advance the carbon footprint of a building, i.e. how construction production affects the environment.

Figure 1 .Table 2 .Figure 1
Figure 1.Assessment of the life cycle in kg CO 2 [Authors´ own work]

Figure 3 .
Figure 3. Carbon footprint of individual buildings in phases A1-A5 in kg CO 2 [Authors´ own work]