BIM-LCA Integration for the Environmental Impact Assessment of the Urbanization Process

: The construction sector is one of the most polluting industries, generating between 30% and 40% of the worldwide environmental burden in terms of raw materials, direct and indirect energy consumption, waste, and CO 2 emissions. Recent advances in computer science and data management have facilitated the evaluation of present and future impacts, thus improving the sustainability of architectural designs. Powerful software tools, such as Building Information Modelling (BIM), allow environmental indicators to be incorporated into the construction elements that make up the project to evaluate it during the design stage. In this work, the state of the art of ecological indicator application through BIM platforms is studied. Barriers and uncertainties are also identiﬁed. Subsequently, a model is proposed to evaluate the environmental impact of an urbanization process or a project through several ecological indicators (carbon footprint, water footprint, and embodied energy). To perform this analysis, the most important aspect is to determine the quantities of each construction element and their clear decomposition into subelements, since both aspects add certainty to the analysis. For this purpose, construction cost databases are a good instrument for introducing environmental awareness. The reliability of LCA data, which can be obtained from generic databases or ecolabels such as environmental product declarations, becomes crucial.


Introduction
Buildings represent between 30% and 40% of worldwide environmental impact, whether directly by their use or indirectly as part of the embodied impact of the construction materials consumed. This encourages architects and engineers to design more sustainable buildings, which implies lower energy and resource consumption [1]. Several tools and calculation models to determine the environmental impact of the construction sector are in place, whether using single issue indicators, such as the embodied energy (EE) or carbon footprint (CF) [2], or more complex ones such as emergy [3,4], the ecological footprint (EF) [5][6][7][8][9], CML, or the eco-indicator, also known as multivariable indicators.
Methods putting together data from the entire construction process are being developed, but the inclusion of environmental concerns during the design stage represents one of the greatest challenges for designers. For this reason, the European Committee for Standardization promotes, in the production phase of buildings, the integration of environmental concerns by defining the European Guidelines on Sustainability in Construction Works [10]. In addition, the European Directive 2014/24/EU on public procurement states that, for public works contracts and design competitions, Member States should use Fortunately, there is always an economic control in construction projects, so all the elements involved are usually well defined in terms of their bill of quantities and budget. This is an opportunity for the introduction of environmental indicators as part of the cost assessment. The tools already in place for the cost control of projects can be adapted for sustainability considerations [8,9]. These tools use the cataloguing code employed by Spanish quantity surveyors to obtain the bill of quantities, which eases the implementation and understanding of environmental impact calculation models [48]. Subsequently, activities are broken down into three types of resources: machinery, manpower, and materials. The methodology developed previously by the authors calculates the embodied energy (EE) [49], the carbon footprint (CF) [50][51][52], and the water footprint (WF) [53,54] of the project, and is suitable for the construction sector thanks to its simplicity and to being introduced as part of the project's budget. The EE, virtual water, and emissions of construction and demolition waste (CDW) management have also been assessed [8].
The previous methodology has been incorporated in two assessment tools: OERCO2 [52] and HEREVEA [55]. The OERCO2 software, which is a result of the OERCO2 Erasmus+ project, is an open-source online tool for the estimation of the CF of new construction residential buildings and is designed to be used by nonspecialized users. Similarly, the HEREVEA tool [55] bases its calculations on the data obtained from the project's bill of quantities to assess the EF of building renovation projects. It also evaluates the economic and environmental feasibility of different proposals simultaneously. The resulting model is then integrated into a geographic information system (GIS), which allows georeferenced results to be obtained. The tool can be used for sustainable and resilient planning, policy-making at all government levels, and decision-making processes. Both types of software have been employed as teaching tools [56,57].

BIM and Environmental Assessment
A general overview of BIM-based tools for environmental impact assessment showed that most of them need to combine the BIM software with other applications to obtain the quantification of environmental indicators. Recently, the advance of BIM worldwide has forced researchers to work on its combination with LCA and LCC (life cycle cost assessment). Various approaches have been followed, which were classified by Santos et al. [26]: those using external individual and separate tools [58]; those connecting quantity take-off and an external LCA database with integrated tools in proprietary software [59]; and the one proposed by Santos et al., based on including LCA and LCC information in BIM models. The main advantage of this last approach is that it quickly updates the analysis results when the project under study is not modified, thus taking advantage of the full potential of BIM tools, while the others require re-exporting the information and re-linking it to the external databases, besides needing extra licenses for the external software involved. In this section, a review of the existing applications regarding these three categories is given to provide a better understanding of the advances in this matter.

Type 1: Exporting Data to External Tools
Regarding this first approach, Jalaei and Jrade [60] developed an integration between Autodesk Revit, Microsoft Excel, and Athena Impact Estimator to analyse the environmental impact and the EE of constructive solutions. Marzouk et al. [61] proposed a combination of several software tools (i.e., Autodesk Revit, Revit DB Link, Microsoft Access, and Athena Impact Estimator) for measuring direct and indirect CE in construction projects.
Chen and Pan [62] presented a multicriteria decision-making method for low-carbon construction measures by combining Revit, eQuest, and Promethee [63]. Ajayi et al. [64] explored a combination of Revit Architecture, Green Building Studio (GBS), and Athena complement for global warming potential (GWP) and health impact assessment. Crippa et al. [65] integrated data extracted from Simapro with Excel and ArchiCad to analyse the CF of wall systems in Brazil. A few external applications can import Examples of tools that apply the second approach (i.e., integration into BIM environments as plugins) are LCA Design, Ecotect, Green Building Studio, One Click LCA, and Tally for Autodesk Revit [31]. Specifically, the latter stands out for its intuitive workflow, technical support, and results presented in a useful format. For example, Najjar et al. [66] analysed a case study with the Tally plugin to evaluate the entire life cycle of buildings, aiming to provide recommendations. Schultz et al. [67] studied the differences in the results of LCA from Tally and Athena Impact Estimator, getting similar results but identifying significant differences in the impact categories.
In this line, Basbagill et al. [58] developed a BIM model using DProfiler linked to eQuest within a BIM environment. Subsequently, the results were manually loaded into SimaPro and Athena EcoCalculator to obtain the CF. BIM has also been combined with LEED and BREAM assessments. Azhar et al. [68] combined Revit with IES Virtual Environment to calculate CE and incorporated energy to convert them into LEED credits. Also, Ilhan and Yaman [24] developed a green building evaluation tool using Graphisoft ArchiCAD ® linked to the BREEAM material database.

Type 3: Including Environmental Data in the BIM Model
Other authors reviewed the existing research on BIM/LCA integration and its possibilities for simplification in terms of input-output data and LCA results [19], and pointed out that the best solution would be to remain within the BIM environment to facilitate the interaction between design and environmental performance assessment [69].
Other environmental evaluation tools and models were defined by Inyim et al. [70], who presented the Simulation of Environmental Impact of Construction (SimulEICon), a BIM extension designed to assist in the design stage of the decision-making process of a construction project. Gan et al. [71] developed a holistic approach to evaluate built-in and operational carbon in high-rise buildings using Revit and a parametric complement, Dynamo. These researchers also evaluated the reduction of the CF by replacing steel and cement with recycled materials [72]. Finally, Yang et al. [73] deployed a unidirectional workflow to calculate the operation and energy of materials and CO 2 eq.

Weaknesses of Other Methods Combining BIM and LCA
In the three different approaches to combine BIM and LCA described in the state of the art, several weaknesses can be identified. In type 1, the main barrier is that the users' objective is to obtain a certificate from an external tool that also requires additional training and knowledge from the designers. In type 2, the designer also needs to learn an additional tool for the environmental analysis. Finally, type 3 is the simpler strategy because everything happens inside BIM, but it is also the most time-consuming in the definition of each element's impact, since LCA data are introduced directly into the BIM software. Thus, if the BIM model changes in any of its components, new LCA data need to be calculated and integrated.

Reliability
As stated in the previous sections, data processing depends on the quality and accessibility of LCA, which vary depending on the source, as presented in Figure 1. Accessibility is when manufacturers make their LCA public. This can be done by using ecolabels, such as EPD, or by less product-specific data, such as the generic data that can be obtained from LCA databases, thus losing reliability [74]. Its robustness depends on the reliability of the consulted sources, since each manufacturer defines the degree of confidence of data by choosing the ecolabel for their products. are adapted to an actual project by defining the geometry, descriptions, and components with BIM, based on the quantity take-off and using more transparent and product specific environmental data from ecolabels. In the third level, environmental indicators or footprints can be calculated and represented for each work unit previously defined in the project. In the last level, the information can be added to the BIM model by means of plugins, directly inserted in the BIM software or by sending the BIM information to environmental assessment tools. Another important aspect is the type of information usually presented in construction projects. These projects employ construction cost databases both to generate and control project budgets and to define a structure and measurement criteria, which are contractually binding and agreed upon in the sector by contractors, designers, and suppliers. To define work units, construction work breakdown systems (WBS) are mainly used. The WBS divides the construction project into small parts that can be easily combined. The most representative are: Standard Method of Measurement of Civil Engineering [75], Uniformat [76], Uniclass [77], ISO 12006-2 [78], and MasterFormat [79].
This widespread tool is a suitable means to introduce environmental assessment in engineering and architecture. In Spain, highly specialized platforms, such as the BEDEC cost database, SOFIAS or E2CO2Cero tools, allow CO2 emissions to be calculated in detail according to the project's bill of quantities. BEDEC was developed by the Institute of Construction Technology of Catalonia [80] and uses environmental data of building materials from the Ecoinvent LCA database [81], one of the most complete databases at the European level [74], which is integrated in the Simapro LCA software [82]. As for the SOFIAS tool, environmental data are obtained from OpenDAP [83]. An intermediate approach is defined in E2CO2Cero by the Basque Country Government in Spain. This approach allows energy and carbon emissions to be calculated due to the materials and processes employed during the building construction [84].
Databases clearly define what should be measured and how it must be done with BIM objects. Therefore, providers must match their environmental information with the way products are traditionally measured and included in the project budgets. This method can be a reliable way of including environmental assessment in construction. The measurement criteria of cost databases can match the quantities obtained from BIM and, simultaneously, the criteria employed in the definition of construction or work units and products by the market, such as square metres of the floor area covered by tiles or cubic metres of concrete in a column. In Figure 1, the first level corresponds both to generic BIM elements for the representation of the project and to generic environmental information of products. In the second level, the previous data are adapted to an actual project by defining the geometry, descriptions, and components with BIM, based on the quantity take-off and using more transparent and product specific environmental data from ecolabels. In the third level, environmental indicators or footprints can be calculated and represented for each work unit previously defined in the project. In the last level, the information can be added to the BIM model by means of plugins, directly inserted in the BIM software or by sending the BIM information to environmental assessment tools.
Another important aspect is the type of information usually presented in construction projects. These projects employ construction cost databases both to generate and control project budgets and to define a structure and measurement criteria, which are contractually binding and agreed upon in the sector by contractors, designers, and suppliers. To define work units, construction work breakdown systems (WBS) are mainly used. The WBS divides the construction project into small parts that can be easily combined. The most representative are: Standard Method of Measurement of Civil Engineering [75], Uniformat [76], Uniclass [77], ISO 12006-2 [78], and MasterFormat [79].
This widespread tool is a suitable means to introduce environmental assessment in engineering and architecture. In Spain, highly specialized platforms, such as the BEDEC cost database, SOFIAS or E2CO2Cero tools, allow CO 2 emissions to be calculated in detail according to the project's bill of quantities. BEDEC was developed by the Institute of Construction Technology of Catalonia [80] and uses environmental data of building materials from the Ecoinvent LCA database [81], one of the most complete databases at the European level [74], which is integrated in the Simapro LCA software [82]. As for the SOFIAS tool, environmental data are obtained from OpenDAP [83]. An intermediate approach is defined in E2CO2Cero by the Basque Country Government in Spain. This approach allows energy and carbon emissions to be calculated due to the materials and processes employed during the building construction [84].
Databases clearly define what should be measured and how it must be done with BIM objects. Therefore, providers must match their environmental information with the way products are traditionally measured and included in the project budgets. This method can be a reliable way of including environmental assessment in construction. The measurement criteria of cost databases can match the quantities obtained from BIM and, simultaneously, the criteria employed in the definition of Sustainability 2020, 12, 4196 7 of 24 construction or work units and products by the market, such as square metres of the floor area covered by tiles or cubic metres of concrete in a column.
Another interesting aspect of construction cost databases is the definition of all the subelements of each work unit. These databases come from a long tradition of cost control in the construction sector, since each element and its quantities are contractually binding. The accurate quantity take-off BIM provides an essential aspect of the environmental impact assessment of projects. Interoperability to determine the amount of material and a cost estimation can accelerate the design process, aid the comparison of alternative solutions, and produce better results [85]. This was already done by Abanda et al. [86], who developed a specific application to link BIM models with the New Measurement Rules (NMR) in the UK standard for public procurement [87] by using the Bath Inventory of Carbon and Energy (Bath ICE) [88]. Also, Mercader-Moyano et al. [89] applied an environmental impact assessment to a BIM environment by using a construction cost database for the quantity take-off.

Materials and Methods
In this section, a method for the calculation of the CF, WF, and EE of urbanization projects is presented. The CF indicator is widely used in the construction sector [90]. However, there are limitations on CF calculations that make the results difficult to compare because the methodologies do not follow a unified international standard [91]. Several examples of the application of the CF indicator to construction projects CF have been carried out using the projects' bill of quantities [50][51][52]. In recent years, advances have been made in defining ranges for the CO 2 of construction elements to make the results comparable [92].
The other two indicators considered in this model, EE [49] and WF [53,54], are of interest to the construction sector due to the simplicity of their message. The EE represents the energy efficiency of the production of products and is independent from the emissions accounting. It is also a useful indicator in construction project assessment [49]. The WF is another interesting indicator to analyse because it determines the amount of this scarce resource employed in the production of goods, being an increasingly important impact in manufacturing. It was developed and standardised following the publication of The Standard Calculation Methodology [93] and The Water Footprint Assessment Manual [94], and is currently disseminated by the Water Footprint Network [95].
The proposed methodology starts with a comprehensive description of the construction project. All the elements in the project should be neatly defined to correctly determine the amount of resources to be consumed. To this end, the WBS of Andalusia Construction Cost Database (ACCD) [96] is used. The ACCD has a bottom-up organization, with the completed project being the highest level of the hierarchy [48]. Each work unit has an associated unit cost and all its components (materials, machinery, and manpower) are described and quantified. The description of these components by an alphanumeric code, which groups units by the material nature or type of common workforce, facilitates the calculation not only of their cost but also of their quantities for similar work units. The levels and examples are illustrated in Figure 2A. On the other hand, measurement criteria are included in each unit description and their subelements in Figure 2B. The set cost per work unit is reinforced by establishing a singular relationship between the measurement criteria established for a given work unit and its corresponding cost. As a result, if the criteria are modified, the cost must be changed. Common measurement units (cubic metre, square metre, thousand units, etc.) are used for similar work units.
Once all the elements necessary to the construction project are codified, information about the nature of each element can be gathered. For example, elements whose code starts with CH are all made of concrete of a certain type, so their impact is assigned from LCA databases. The weight of each material can be determined by their quantities, obtained through the geometry of BIM construction objects. Each step is explained in detail in the following paragraphs. Once all the elements necessary to the construction project are codified, information about the nature of each element can be gathered. For example, elements whose code starts with CH are all made of concrete of a certain type, so their impact is assigned from LCA databases. The weight of From each machine employed in the project, fuel consumption is considered its main environmental impact, which is linked to its engine power (fuel and electricity) and working hours [97]. The average Sustainability 2020, 12, 4196 9 of 24 fuel consumption of machines is from 0.15 to 0.20 for diesel engine, and from 0.30 to 0.40 L/h/kW for petrol [98].
The fuel consumed is obtained as specified in Equation (1): where V: Fuel consumption (L); P: Engine power (kW); Wh: Working hours (h); and R: Engine performance (L/kWh). As for electrical machines, energy consumption is calculated as defined in Equation (2):  [8]. To obtain the CO 2 emissions, water consumption, and EE of construction materials, their Life Cycle Inventory (LCI) is analysed by applying the IPCC 100a and Water Footprint and Cumulative Energy Demand methodologies provided with Simapro v8. The environmental information is extracted from the EcoInvent database through SimaPro, since this database covers the vast majority of materials usually employed in construction [6].
In the BIM project, the quantities of construction materials (Qi) are determined, e.g., the number of benches, the cubic metres of concrete in the road, or the square metres of tile area in a sidewalk. When the environmental impacts of each work unit are already included in the ACCD, see Figure 3, they can be multiplied to obtain the total impact of the element or unit cost, as shown in Equation (3): where I i is the impact (WF, EE or CF), and U i is the total impact in the construction unit i.
Sustainability 2020, 12, x FOR PEER REVIEW 9 of 24 each material can be determined by their quantities, obtained through the geometry of BIM construction objects. Each step is explained in detail in the following paragraphs. From each machine employed in the project, fuel consumption is considered its main environmental impact, which is linked to its engine power (fuel and electricity) and working hours [97]. The average fuel consumption of machines is from 0.15 to 0.20 for diesel engine, and from 0.30 to 0.40 L/h/kW for petrol [98].
The fuel consumed is obtained as specified in Equation (1): where V: Fuel consumption (L); P: Engine power (kW); Wh: Working hours (h); and R: Engine performance (L/kWh). As for electrical machines, energy consumption is calculated as defined in Equation (2):  [8]. To obtain the CO2 emissions, water consumption, and EE of construction materials, their Life Cycle Inventory (LCI) is analysed by applying the IPCC 100a and Water Footprint and Cumulative Energy Demand methodologies provided with Simapro v8. The environmental information is extracted from the EcoInvent database through SimaPro, since this database covers the vast majority of materials usually employed in construction [6].
In the BIM project, the quantities of construction materials (Qi) are determined, e.g., the number of benches, the cubic metres of concrete in the road, or the square metres of tile area in a sidewalk. When the environmental impacts of each work unit are already included in the ACCD, see Figure 3, they can be multiplied to obtain the total impact of the element or unit cost, as shown in Equation (3): where Ii is the impact (WF, EE or CF), and Ui is the total impact in the construction unit i.  The proposed methodology is represented in Figure 4.
Sustainability 2020, 12, x FOR PEER REVIEW 10 of 24 The proposed methodology is represented in Figure 4.

Results
In public spaces, playgrounds and parking lots are useful for the introduction of environmental awareness to the urban planning of cities. For this, a small urbanization project is defined for the illustration of the proposed methodology. The project includes a playground (12 m × 22 m), a parking lot (20 m × 22 m), a section of road (40 m × 6 m), the corresponding sidewalk (40 m × 2 m), and a cycle path (40 m × 2 m). As expected for this type of construction site, concrete and asphalt are the main materials but others are also used, such as wood for benches and metal for the playground and street lighting.
As Table 1 shows, it was possible to define classification equivalences between BIM (or IFC) elements, codes from Uniclass, and complex costs (CC) from the ACCD, thus calculating their environmental impact in terms of the three indicators considered in this study, i.e., EE, CF, and WF. A short description of each CC, along with their economic cost and environmental impact, is also shown in Table 1. The 19 CC defined for the case study comprised 68 unit costs (UC). For each, the unit impact was determined by adding the impact of their basic components (BC). The complete list of the elements included in these CC is presented in Table A1 of Appendix A, with the corresponding cost and environmental impact.

Results
In public spaces, playgrounds and parking lots are useful for the introduction of environmental awareness to the urban planning of cities. For this, a small urbanization project is defined for the illustration of the proposed methodology. The project includes a playground (12 m × 22 m), a parking lot (20 m × 22 m), a section of road (40 m × 6 m), the corresponding sidewalk (40 m × 2 m), and a cycle path (40 m × 2 m). As expected for this type of construction site, concrete and asphalt are the main materials but others are also used, such as wood for benches and metal for the playground and street lighting.
As Table 1 shows, it was possible to define classification equivalences between BIM (or IFC) elements, codes from Uniclass, and complex costs (CC) from the ACCD, thus calculating their environmental impact in terms of the three indicators considered in this study, i.e., EE, CF, and WF. A short description of each CC, along with their economic cost and environmental impact, is also shown in Table 1. The 19 CC defined for the case study comprised 68 unit costs (UC). For each, the unit impact was determined by adding the impact of their basic components (BC). The complete list of the elements included in these CC is presented in Table A1 of Appendix A, with the corresponding cost and environmental impact.
After connecting the CC to the BIM model of the urbanization project, those elements that should be first addressed to reduce the project's WF, EE, or CF were visually identified (see Figure 5). BIMVision software by Datacomp was employed to represent the results. The software was combined with a plug-in specifically created to visualize the environmental impact of each element in the model, which was part of the deliverables of the UrbanBIM Erasmus+ project. As Figure 5 shows, in the specific case of the CF, the parking area and the sidewalk generated the greatest impacts, even though their unitary impacts were low (see Table 1). Similar results were obtained from the other two indicators (WF and EE); again, two big elements, the parking lot, as previously mentioned, and the driveway had the highest impact. The incorporation of bituminous materials (from petroleum) and tars (from coal) into the road pavement involved the incorporation of very significant amounts of EE, and, in the case of aggregates, high water consumption.  The methodology could be extrapolated to a complete construction cost database to define the BIM model and its impact with a tool based on cost control. The biggest difficulty is the amount of information to be transformed. In the case of the ACCD, this needs to be done for over 7000 elements. The smallest impact was based on each wooden bench, a small element in the project that was made of a low-impact material. However, the size was not the only defining aspect: for example, the cycle path and the sidewalk had similar sizes but the CF impacts were represented in different colours (green and brown, respectively). This indicated that the concrete tiles placed on the sidewalk had a greater impact than the poured concrete used in the cycle path. The tiles also had more impact than the biggest element in the project, the driveway. In the results obtained by Freire et al. [9], asphalt and concrete were also the highest-impact materials in the evaluation of urbanization projects.
The methodology could be extrapolated to a complete construction cost database to define the BIM model and its impact with a tool based on cost control. The biggest difficulty is the amount of information to be transformed. In the case of the ACCD, this needs to be done for over 7000 elements. The big advantage is that the indicators selected are easy to understand, and some degree of automation can be achieved.

Discussion
This study shows that it is possible to incorporate ecological indicators, such as WF, CF, and EE, into the classification system of construction cost databases through the methodology developed by the ArDiTec research group. When working on the sample urbanization project, the definition and use of new work units, complex and unit costs were required to integrate them into the ACCD classification system, specifically the urbanization chapter of the work breakdown system, which is focused on the elements related to the connections of buildings with urban networks.
The elaboration of a calculation matrix with the environmental data obtained from the LCA databases for each element, which was part of the various work units, became necessary, thus making it possible to carry out the assessment through the developed plugin for the employed BIM environment. The correct definition of the system boundaries and their components by means of the work units and their elements avoided the gaps andoverlaps that usually happen in construction cost assessment.
The design of the system was totally transparent, resulting in an easy and intuitive tool. A major challenge was to define the BIM elements properly to match the work units. Lützkendorf et al. [85] found that BIM could determine the amount of materials and cost estimation, which can be helpful for the environmental assessment. Mercader-Moyano et al. [89] applied a different strategy by combining costs with the environmental assessment using BIM to define the composition of work units in the case of a reinforced concrete structure. The amount and section of the reinforcement bars was then represented in the BIM elements, and their environmental assessment was calculated. Rock et al. have also studied how to combine BIM, a cost database in Switzerland, and its work classification system in the environmental assessment of building construction [99]. This also identified the importance of concrete in buildings.
The most important contribution of the present work, besides showing how the LCA can be graphically represented in urbanization projects, is that traditional construction cost databases are proven to be an instrument for the introduction of environmental assessment to the construction sector, since its use is widespread and agreed on by stakeholders in the sector, such as constructors, promoters, engineers, and architects. The way elements are traditionally measured in the market becomes the key to defining the LCA data associated with them. In urbanization projects, as well as in building construction, cost data can be employed both to define the BIM model and to obtain the bill of quantities.
There are also limitations to this study: in order to implement BIM and environmental assessment in urbanization projects, it is necessary to have a combined strategy for the standardization of work units, together with the breakdown systems for information classification. It is also necessary to have a clear definition of the system boundaries in order to compare different projects. For this, all construction units in the cost databases need a regularized methodology of environmental impact assessment.

Conclusions
Scattered urbanization projects are frequent in cities; the basic components are repeated in many of them, but because of small sizes, the introduction of an environmental assessment is difficult at the moment. Nevertheless, cost control always takes place in publicly funded projects. This helps to introduce the assessment by combining BIM representation with construction cost databases.
The databases, their internal cost structure, and a classification of works allow the resources employed in a project to be determined accurately. Classification equivalences make it possible to include the calculation of environmental indicators, i.e., EE, CF, and WF. Construction cost databases and environmental assessment could be combined by defining the equivalence between BIM elements and their corresponding unit costs.
Data processing depends on the quality and accessibility of LCA data, which vary depending on the source: eco-labelling, such as EPD, or less product-specific data, such as generic LCA databases. Moreover, the robustness depends on the reliability of the sources consulted, since each manufacturer, by choosing an eco-label for their products, defines the degree of confidence of the data provided. The previous data are adapted to a specific project by defining the geometry of BIM objects. Also, environmental indicators or footprints can be calculated and represented for each construction unit previously defined in the project. The information can then be added to the BIM model through plugins, directly inserted in the BIM software or sent to environmental assessment tools.
One of the biggest setbacks to the environmental evaluation of projects in BIM is the complexity of the information, as the LCA integration with BIM requires programming skills, thus making the assessment a multidisciplinary task necessitating that environmentalists, architects, engineers, and programmers work together. The construction cost databases traditionally used in the sector to generate and control the project budgets define a structure and measurement criteria for each work unit, which is contractually binding and agreed upon in the sector by constructors, designers, and suppliers. This becomes an opportunity for introducing environmental awareness and an economic control into the sector, supported by BIM visualization tools.
In forthcoming research studies, other type of projects could be assessed, from single housing to high-rise buildings, to analyse in detail the limitations and opportunities of combining BIM, cost, and environmental analysis. Also, the different stages of the building life cycle can be addressed using the proposed methodology by assessing construction or successive renovation or maintenance projects that take place during the life span and the corresponding budgets.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. The European Commission's support for the production of this publication does not constitute an endorsement of the contents, which reflect the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein.