Various environmental reports carried out in recent years highlight the construction sector as one of the main consumers of energy and generators of CO2
emissions among the various industrial sectors, with estimates of 30–40% of the total environmental impact produced [1
]. This concern has forced the appearance of different types of tools to assess these impacts: through certification and standardization, the promotion of international standards to use environmental labeling for construction products [2
], the development and application of life cycle analysis (LCA) [6
], and the environmental management of buildings from a life cycle perspective [9
]. However, the implementation of these standards is not always easy to achieve, due to barriers of all kinds, economic, technical, practical, and cultural, which prevent professionals from selecting materials with less environmental impact [11
If we focus on the analysis of the life cycle of buildings, the manufacturing and construction phase of the building life cycle, concentrated in a short period of time (1–2 years), causes the most intense environmental impact, mainly due to the consumption of concrete and steel for the structure, which represents a high percentage of the emissions produced during this phase [13
]. This impact is diluted if the building’s useful life is lengthened. The use and maintenance phase is generally responsible for 80–90% of the CO2
emissions generated during the life cycle of the building [15
], almost 60% of which is caused by the demand for energy for heating and cooling [16
]. This implies that, in new standards such as zero energy buildings, emissions during the construction phase represent a higher percentage of the total emissions throughout the life cycle [17
]. Therefore, once the energy consumption during the use phase is reduced, researchers’ attention should be focused on materials that require less energy for their production [18
Most of the recent studies that propose methodologies to estimate the environmental impact of buildings or the application of ecological indicators to the case studies of buildings have focused on aspects such as LCA [19
], the analysis of energy consumption throughout of the life cycle [20
], the carbon footprint of the life cycle [21
], or a combination of these methods [22
]. In recent years, these studies have been incorporated into more powerful computing tools, which is generating a new field of action for LCA, as is the case for building information modeling (BIM) platforms [24
However, the LCA methodology and its derivatives are not always easy to implement by non-specialized users, and neither is their communication. For this reason, other methodologies have been implemented that have a smaller scope but are easier to use and implement by the agents involved in construction. Among the most employed, we find the ecological footprint (EF) or the carbon footprint (CF). The CF is an indicator of emissions of greenhouse gases generated by a given process [25
], which stands out due to its simplicity and direct relationship with the main objectives of the Kyoto Protocol [26
], along with its easy application in decision-making and environmental policy [27
]. There are a large number of bibliographic reviews related to the use of the CF indicator in construction [28
], however, the results are not always comparable, due to the absence of a methodology that follows international standards [29
]. For this reason, studies have also been carried out in recent years to establish scales that allow for the definition of reasonable ranges of CO2
emissions in construction processes [30
Tools are in place that can ensure that new and already built buildings meet minimum requirements related to environmental sustainability. Most of these systems are currently developed by two international organizations [31
]: the World Green Building Council (GBC), which develops tools from an international system to obtain sustainability data for buildings, adapting them to each country, and BRE Global is another independent organization that develops the BREEAM method.
In Spain, there is a variety of these tools that include the calculation of the CF of buildings in some way, for example, LEED or BREEAM, whose use has spread in the country thanks to national organizations such as the Spanish Green Building Council [32
] and BREEAM Spain [33
]. These tools include, among the categories evaluated, the CO2
emissions due to the production of construction materials and the operational energy consumption; however, the final score does not reflect these CO2
emissions, so it does not report each result separately for a better understanding and subsequent analysis of possible improvements.
However, other alternatives have emerged from various research projects in the last decade in Spain. For example, SpainGBC has presented VERDE tools [32
], a set of environmental impact assessment tools for design assistance (HADES), new buildings (VERDE NE), rehabilitation (VERDE RH), and urban development (VERDE DU). In this set of tools, the CF obtains the highest percentage of the score, so it prevails over other sources of environmental impact. ECOMETRO is an open-source and online tool to measure the environmental impact of buildings [34
]. The information generated is similar to an environmental product declaration (EPD), but it applies to entire buildings.
Highly specialized platforms such as the BEDEC cost database, SOFIAS tool [35
], or E2CO2Cero [36
] allow for the detailed calculation of CO2
emissions according to the bill of quantities of a project. BEDEC was developed by the Institute of Construction Technology of Catalonia (ITeC), and uses environmental data of construction materials from the Ecoinvent database [37
], known for being one of the most complete environmental databases at the European level [38
] and for its integration with Simapro LCA software [39
]. The SOFIAS tool uses data from the OpenDAP database [31
]. An intermediate solution is E2CO2Cero [36
], supported by the Basque Government, which is a software that estimates the embodied energy and CF of a building according to the materials consumed and the construction processes [36
]. This tool also has two different versions: complete and simplified. The first one requires the presentation of the bill of quantities of the project, which is considered the appropriate way to reach the general public and create social awareness. A table with the scopes of each tool is included (Table 1
In Romania, the awareness of green buildings and sustainable building materials has increased significantly over the past 10 years. The first LEED and BREEAM certifications appeared in 2008–2009. Currently in Romania, there are 39 buildings with BREEAM certificates, 21 with LEED, 3 with DGNB (German Sustainable Building Council) [40
], and more than 4600 houses and apartments certified or in progress within the GREEN HOMES certification scheme developed by the Romania Green Building Council (GBC) [41
The tools used by Romanian evaluators to calculate CO2
emissions of buildings are One Click LCA, Integrated Environmental Solution (IES VE Pro) [42
], GaBi [43
], 360 Optimi [44
], and others. All of these require data on the type of material, the name of the product, thickness, quantity, transport (distance and type), and durability.
Colliers International Romania used One Click LCA to calculate the entire building life cycle assessment for their first LEED v4 project, as part of LEED certification. The project aimed to achieve a Gold Level certification [45
]. GaBi software [43
] supported a study on the LCA methodology applied to optimize municipal solid waste management (MSW) systems in Cluj county, Romania.
Romania GBC has established procedures for EPDs to be easily integrated into environmental certification tools such as GREEN HOMES [41
] and is promoting EPDs for the recognition of points in international LEED or BREEAM certification. In the case of the Living Building Challenge certification system, its materials category is designed to foster a successful materials economy that is non-toxic, transparent, and socially equitable [46
In Romania, there is no accredited body to issue EPDs, and all declarations are issued by international entities. The National Institute for Research and Development in Buildings, Urban Planning and Regional Sustainable Development (URBAN INCERC), established in 2009, is the only recognized institution that tests materials and issues performance certifications.
Compared to Spain, in Romania, there are no tools such as the BEDEC cost database, SOFIAS, or the E2CO2Cero tool that can be used to calculate CO2 emissions. There is cost-estimating software based on the quantities of materials, labor, transportation, and equipment used for buildings, but they do not include parameters such as energy consumption, CO2 emissions, or other environmental data.
From this point of view, an instrument capable of estimating the CF of buildings, which is also available in Romania, is a necessity nowadays and may be important for the future development of the construction sector due to the possibility of increasing the awareness of all participants in the construction industry regarding environmental problems.
The experience of the authors in methodologies for calculating carbon footprints (CFs) is presented through an open-source software to estimate the CF of architectural projects from the design phase and the tool is part of the OERCO2 project [47
]. It is developed for educational purposes and free access with an Erasmus Project granted by the European Union, and member countries include Spain and Romania. This research is part of the tool validation for the calculation of carbon emissions in the construction phase of the building life cycle [47
]. In the present work, the OERCO2 tool evaluates the CO2
emissions of the construction phase, including the extraction and manufacture of materials, as well as the management of construction and demolition waste (RCD) and the economic impact, and is compared to the rest of the tools in Table 1
. Even though it does not cover all the aspects, it is easy to use and free accessible, making it an interesting teaching tool for college students and professionals [47
]. The tool is valid to evaluate projects at the design stage.
The performance of this tool is explained through a comparative analysis of projects in both countries, Spain and Romania, which are part of the OERCO2 project. Representative typologies are assessed. In the particular case of studies in Romania, the CF of seismic reinforcements [49
] is assessed. Additionally, a sensitivity analysis of the tool in these case studies is done.
A list with corresponding acronyms is included: Life cycle analysis (LCA); ecological footprint (EF); carbon footprint (CF), Green Building Council (GBC); Andalusian construction information classification system (ACICS); basic costs (BCs), auxiliary costs (ACs); simple unitary costs (SCs); life cycle inventory (LCI); metallic structure (MS).
4. Results and Discussion
According to the characteristics of the projects proposed from the statistical analysis of each country, the 48 projects’ data are classified and coded according to the OERCO2 tool information in Table 8
and average values are obtained, the numbers are generic for the software and do not have a specific meaning. The comparison is not only of Spanish and Romanian projects but also different constructive solutions are employed in each country that give rise to 24 combinations in each (Table 8
). The codes are defined to identify the differences in the combinations as set in Table 8
: column foundation, number underground floors, ground floor, and roof type. The MS and CS coding corresponds to the typical metal structure projects in Romania and the concrete structures of the projects in Spain, respectively. The numeric codes are those internally used by the software.
From the building typology and construction characteristics of the projects, the unit (Qi) and total (Qt) quantification of each project is obtained, from which the economic and CF results are obtained, and included in Supplementary Data Tables S1 and S2
(Romania and Spain, respectively).
The quantity of materials used in the projects is analyzed according to the weight, expressed in kg, in addition to the CF, and, finally, the CF is calculated for the construction phases of the projects. Materials are grouped in families: concrete and cement, ceramics and bricks, aggregates and stones, and metals and alloys represent around 80% of the total weight.
In Figure 4
, the materials are analyzed according to the weight of metallic structure (MS) buildings in Romania, and in Figure 5
, concrete structure (CS) buildings in Spain. Buildings with an MS need a larger amount of materials, except in the case of aggregates, whose values are similar in both cases. Concrete and cement are the heaviest materials in both countries. Pile foundation buildings have the highest consumption, followed by those of isolated footings and finally of reinforced slab. Ceramics and bricks have a higher consumption in Romanian buildings, since façade cladding is thicker than in Spain. Aggregates and stones are used almost equally in the three types of foundations. Lastly, metals and alloys have a higher consumption, as expected, in MS buildings.
The analysis of the CF of materials introduces a new important family, plastics. Figure 6
shows that MS buildings in Romania produce a greater impact than those in Spain with CS (Figure 7
) for all the families, except plastics, due to the use of projected polyurethane insulation in CS buildings. In MS projects (Figure 6
), metals/alloys and concretes/cements produce the greatest CF, as the buildings with piles produce a slightly greater impact compared to the other two types. Ceramics/bricks also produce high CF values, due to their use in façades and interior cladding, and lastly plastics. However, in the case of CS buildings (Figure 7
), the greatest impact is produced by concretes/cements, with those with piles and isolated footing being more polluting than those of reinforced slab. Ceramics/bricks have a much smaller impact, since Spanish buildings have less thick façades than Romanian ones, followed by metals and alloys, and then plastics. These results are similar to those of other studies [48
The patterns in Figure 4
, Figure 5
, Figure 6
and Figure 7
are due to the project classification in Table 6
, first fixing foundations, then the number of underground floors, followed by the type of construction, such as ground level use, and, finally, the roof type.
Simple costs included in the OERCO2 tool with the greatest impact (according to the ACCD) are 3HAL00002 (m3 slab concrete); 03HMM00002 (m3 mass concrete); 03CPS00007 (m pile on site); 05HHJ0010 (m3 concrete assembled on beams); 05FBB00007 (m2 waffle slab with concrete caissons); 05FUS00007 (m2 one-way slab with concrete vaults); 05ACS00000 (kg steel in hot-rolled profiles); 05HAC00015 (kg corrugated steel in bars); 06LMM00101 (m2 one-foot brick wall); 06LPC00001 (m2 0.5-foot brick wall).
The following analysis is carried out by the construction phases or chapters of the project, as shown in Figure 8
(Romania) and Figure 9
(Spain). It is observed that the chapter with the greatest impact is structures in MS buildings and then the chapter of installations in CS buildings, due to solar panels, which have been mandatory in the construction of new housing in Spain since 2006. The next chapter that produces the greatest impact is masonry, in both countries, including ceramics/bricks for their use in façades, claddings, and partitions. The next important CF value is produced by the foundation phase, with the piles producing the greatest impact in both countries, followed by isolated footings and, lastly, with little difference, reinforced slabs. Of the five chapters, the one with the least impact is that of finishes, with similar values in all the cases analyzed since there are no variations in the construction systems and/or materials used.
A sensitivity analysis of the CF produced by each of the different phases of the projects in each country is carried out, according to the percentage they represent of the total project, which is essential for decision-making at the design level in order to focus on the chapters with the greatest impact and to be able to reduce project emissions using more sustainable materials, based on the obtained results of the analysis.
Thanks to the data obtained from the OERCO2 tool, this analysis can be carried out, and it is presented in Table 9
and Table 10
, depending on whether they are from Spain or Romania, respectively, and grouped according to similarity in terms of building typology.
Thus, in the case of projects in Spain with a concrete structure (Table 9
), it can be seen that the foundation for piles is the one with the highest CF, with values between 11.23% and 12.73% of the total project impact. The reinforced slab has the lowest CF, 3.57% less than piles.
In the chapter of structures, it is observed that buildings without underground floors have a higher CF than the rest, and in particular those with foundations with isolated footings, with a 2.01% difference from those with a lower CF, which are the buildings founded on piles and with a basement.
In the masonry and installation phases, it can be seen that the buildings that have commercial premises on the ground floor produce higher CFs, the difference being 2.43% for masonry and 1.99% for installations, between the highest and lowest CF projects.
Regarding cladding, the highest CF corresponds to buildings with the highest number of basement floors and without premises on the ground floor, with a difference of 1.08% between those with the highest and lowest value.
In the case of the projects in Romania with a metallic structure (Table 10
), the projects with foundations of piles are those with the highest CF, with a difference of 2.86% with respect to the lowest CF, which are those with reinforced slab and without a basement. With respect to Spanish projects, they represent a lower percentage of the total, with an average difference of 2.50%.
The (metallic) structure in the Romanian buildings is the phase with the greatest impact on the project, and it is the foundation with footings that produce the highest CF, 2.72% higher with respect to the reinforced slab and two basement floors. With respect to Spanish concrete structures, they have a much higher CF in all cases, the average difference being 14.48%.
In masonry and installations, the situation is similar to Spanish buildings, those with premises on the ground floor and no basement have a higher CF than those without premises and consist of one or two basement floors, with a difference of 2.14% for masonry and 0.61% for installations between the highest and lowest with respect to the total CF of the project. The masonry values are very similar to those of the buildings in Spain, however, in the installations, by including the solar panels in Spain, the CF is higher by an average value of 8.59%.
Cladding has a similar impact in both countries, buildings without premises and with more basement floors produce a higher CF than those with premises on the ground floor and without a basement, with a difference of 1.20% between those of greater and lesser value. With respect to Spain, Romania has a lower CF of 1.56%.
Finally, an economic and environmental comparison is carried out (Table 11
). The economic analysis highlights that MS buildings are more expensive per m2
than CS buildings, and in both cases a pile foundation is the one with the greatest economic impact, followed by isolated footings and reinforced concrete slab. The OERCO2 costs are based on Spanish data.
The Romanian construction cost can be translated into Spanish cost by normalization tools such as European Construction Cost data [73
], the coefficient for Spanish costs is 0.7052 and for Romanian costs, it is 0.464. In the present work the Spanish costs are used for both countries in order to facilitate the results comparison (Table 11
Regarding the CF, MS buildings produce the highest emissions and pile foundations produce the greatest impact in both types of buildings, followed by isolated footings and, lastly, reinforced slab. These results are similar to others [68
]. Materials (including their transport) are responsible for 95–97% of project emissions. The remaining percentage corresponds to machinery.
Muñoz et al. (2012) [75
] carried out a study of the CF of social housing built in Chile, focusing on the LCA of construction materials, which included its implementation. The results showed that the energy of commissioning is negligible, while 35% corresponds to the extraction and manufacture of materials, and 65% to the use and maintenance. In addition, there are bibliographic reviews related to the use of the CF indicator in construction [28
], however, the results are not always comparable due to the absence of a methodology that follows international standards [29
]. For this reason, studies have also been carried out in recent years to establish scales that allow for defining reasonable ranges of CO2
emissions in construction processes [30
The OERCO2 tool is valid to compare constructive solutions between different project partner countries (in this case, Romania and Spain), because the tool includes the representative characteristics of the buildings in the partner countries. The tool allows for analyzing different constructive systems, in this case, the different types of foundations, structures, masonry, or installations that have been proposed. Therefore, it is possible to determine which constructive solution has the least impact from an economic and environmental point of view. According to the analyzed cases, the most efficient typologies are reinforced concrete buildings, with a significant difference with respect to metallic structures, both economically and environmentally.
For the 48 analyzed typologies, the families of materials that produce the most emissions are: metals/alloys, concretes/cements, and ceramics/bricks and, to a lesser extent, plastics. The structures, installations, foundations, and finishes produce the greatest impacts.
The OERCO2 tool evaluates a project’s CF and economic impact simultaneously at the design stage and in detail, according to the project phases, such as earthwork, foundation, structure, etc. Decisions can be made regarding the construction systems and materials used in order to reduce emissions and economic impact, thus helping to understand and improve the eco-efficiency of projects. Therefore, OERCO2 can be a useful educational tool for architecture and engineering college students.
Of the types of foundation assessed both economically and environmentally, piles produce the highest emissions and cost, and the best option is reinforced slabs followed by insulated footings. The building ground floor use, as a dwelling or premises, also influences cost and emissions, especially in phases such as masonry, installations, or finishes.
All these analyses are important to decide how to design in the most environmentally friendly and economical way. The tool facilitates the decision-making of promoters and technicians, without needing prior knowledge about environmental indicators.