Building rehabilitation versus demolition and new construction: economic and environmental assessment

1 Building rehabilitation versus demolition and new construction: economic and environmental assessment Abstract Since the end of the twentieth century, discussion on dwelling rehabilitation versus its demolition and new construction has been steadily increasing in intensity, which is especially due to the necessity for the regeneration of urban centres. However, rehabilitation is not always considered the most economical solution, and demolition and new construction may constitute a better option. In the present work, a multi-family building in Seville, Spain, is used as a case study. After having suffered damage from a construction failure, it is assessed for its complete rehabilitation. Defective maintenance has worsened the bad condition of the building. A model is proposed, from the project budget perspective, that allows the environmental (Ecological Footprint indicator) and the economic (project´s bill of quantities) assessment of the recovery of the dwelling. In the case study, the rehabilitation ecological footprint and the project cost are 0.06 gha/m2 of floor area (457.22 EUR/m2) and 0.14 gha/m2 (576.33 EUR/m2) for a new building on the same plot, respectively. It can be deduced that, even with a severely damaged building, the repair and retrofit work incurs a lower economic and environmental impact than that of the total replacement with a new construction. Keywords: Building rehabilitation; work breakdown system; emergency condition; ecological footprint 2 Introduction Discussion on dwelling rehabilitation versus its demolition and new construction has been increasing in intensity since the end of the twentieth century, especially due to the necessity for the regeneration of urban centres caused by the great migration from rural to urban areas (Denhez, 2007; Laefer and Manke, 2008; Rakhra, 1983). In the European Union, entire neighbourhoods were re-built shortly after the Second World War. Now they fall short of meeting current needs (insufficient and outdated installations, poor insulations, obsolete equipment, among others), therefore neighbourhoods formed by these types of dwellings are under continuous threat of mass demolition (Power, 2010, 2008). For over a decade, it has been predicted that building rehabilitation would be the dominant activity in the construction sector (Kohler and Hassler, 2002). Financial aspects tend to tip the balance towards building rehabilitation rather than demolition and new construction (Itard and Klunder, 2007), except in those cases where the building is so damaged that rehabilitation costs reach the levels of new construction costs. Studies usually focus on the potential for energy savings in buildings once renewed (Goldstein et al., 2013), but there have been suggestions for the evaluation of these savings along with other aspects, such as the increase in value of a building or the improvement of the conditions of its components (Martinaitis et al., 2004; Zavadskas et al., 2008). Other proposals are more detailed and deal with energy prices, the hypothesis of an increased use of renewable energy, maintenance costs, or financial interest rates (Morelli et al., 2014). However, the need to include not only economic, but also environmental and social aspects in this analysis has increased over time, as these factors are all part of the concept of sustainability (Thomsen and van der Flier, 2009). In this paper, the rehabilitation of a building under emergency conditions after a construction failure is assessed in detail. The analysis incorporates the improvements necessary to make a building habitable, as well as the repairs and maintenance needed to improve the comfort of tenants (Ferreira Sánchez, 2015). In order to take into account as many variables as possible in this difficult decision of rehabilitation vs. demolition and new construction, a model is proposed from the project budget perspective that allows both the economic (project’s bill of quantities and budget) and environmental (Ecological Footprint indicator) assessment of these two options. 3 The Andalusian Construction Cost Database (ACCD) (Andalusia Government, 2014) is used for the cost assessment, and new rehabilitation costs, which are not included in the database, are created using its work breakdown system. For the environmental impact assessment, the Ecological Footprint (EF) indicator (Wackernagel and Rees, 1997) is employed. The EF is the amount of land that would be required to provide the resources (grain, feed, firewood, fish, and urban land) and absorb the emissions (CO2) of humanity. The EF, along with the Carbon Footprint, have become two of the most widespread indicators thanks to the simplicity of their concept (as compared to LCA assessment) and their ability to place sustainability on the agenda. However, due to the major simplification of such an extremely complex process as that of the environmental impact on Earth caused by humans, certain flaws regarding its scientific value have been highlighted by several authors (Fiala, 2008; Grazi et al., 2007; Van Den Bergh and Verbruggen, 1999). Despite these flaws, EF has been employed in the development of various assessment systems for construction projects such as: structural sustainability in BIM (Oti et al., 2016), dwelling construction (Bastianoni et al., 2007; González-Vallejo et al., 2015a; Solís-Guzmán et al., 2013), urbanization of rural land (Marrero et al., 2017), and building maintenance and cleaning tasks (Martínez-Rocamora et al., 2016a). On this basis, the proposed model will assess the feasibility economic and environmental of the renovation of a building that is facing demolition, specifically analyzing a case study of 40 social housing dwellings with severe structural damage located in the city of Seville. The authors’ previous models are employed for the assessment of the economic cost and EF of construction and urbanization processes (Freire and Marrero, 2014; González-Vallejo et al., 2015b; Solís- Guzmán et al., 2013). 1. Literature review Regarding the topic of this study, Bullen and Love (2010, 2011) came to the conclusion that the three key criteria for decision-making in cases of renovation versus demolition and new construction were the investment costs, the building conditions, and the regulations. Other factors, such as environmental, economic and social principles, were relegated to having less influence. Itard and Klunder (2007) studied the environmental effects of the life cycle of buildings in terms of time, concluding that, in a scenario in which a building lasts 100 years, the total energy 4 consumed over the lifetime of the building is higher if the dwelling is either kept as-built or demolished and newly constructed, and lower if refurbished. Reconstruction poses a significant environmental impact, but also offers opportunity for the improvement in the energy efficiency of the building. Along the same lines, Verbeeck and Cornelis (2011) analysed the renovation versus demolition and new construction of a portion of the dwelling stock in Belgium under different scenarios, from an energy, economic and environmental point of view. They concluded that the annual energy savings did not justify demolition and new construction, and that this option would only make sense if the building were in an extremely poor condition for habitation and if the rehabilitation were going to incur a major cost. From the environmental point of view, they conclude that demolition and new construction is not necessarily a worse option than renovation. The energy savings that can be achieved are greater when replacing the building with a new construction where waste reuse and recycling is maximized in demolition work. Dobbelsteen et al. (2004) designed a methodology for the simplified mathematical analysis of the environmental impact of renovation versus demolition and new construction. This method is based on the allocation of specific environmental costs and of annual environmental costs, with the former relating to the construction, demolition, and possible renovation, and the latter to the costs of the consumption of energy and other resources on an annual basis. In their model, it is assumed that the renovation or new construction should lead to a reduction of annual costs, since the renovated (or new) building should be more energy efficient. One of the most interesting alternatives to demolition and new construction consists of the reuse of existing buildings and their expansion. Thus, the potential waste generation and consumption of resources are reduced, while the reuse of materials is maximized (Chapman et al., 2003, 2002, 2001). Logically, this solution is conditioned by the feasibility of reuse of the building components. Laefer and Manke (2008) conducted a study on the partial or total reuse of buildings in which it was concluded that reuse can produce savings of 4% to 65% depending on the utilization of the existing building. In addition, new buildings use four to eight times more material resources than the equivalent rehabilitation (Ireland, 2008; Yates, 2006). According to Sezer (2012), the existing methods of analysis of the environmental impact of buildings focus on the construction of new buildings. In these models, the variations in 5 productivity, efficiency and short- and long-term consequences in the rehabilitation work are not covered: hence the need to create arises for the creation of a methodology for the quantification of resources and for the calculation of environmental impact that is applicable to rehabilitation. The previous models of the authors are used for the evaluation of the economic cost and EF of the construction and urbanization processes (Freire and Marrero, 2014; González-Vallejo et al., 2015b; Solís-Guzmán et al., 2013). The model proposed in this paper will evaluate for the first time the renovation of a building that faces demolition through the evaluation of economic and environmental aspects, making necessary a new approach that replaces normally used unitary costs of constructions project by complex costs; the last are completed buildings elements (facades including its finishes, foundations including auxiliary’s elements, etc.), this way deteriorated elements con be analysed as a construction project. 2. Methods and materials The proposed model aims the technical, economic and environmental evaluation of the rehabilitation of buildings that are facing a demolition and new construction. The model is divided into three phases. First, a rehabilitation cost database is created that allows the economic evaluation of this type of work. Second, the evaluation of the environmental impact is carried out by means of the adaptation and application of the HE model to the rehabilitation of buildings. Third, an integration process of the economic and environmental costs is carried out, through the creation of what has been called the resource quantification bank, which consists of disaggregating the different construction units into machinery hours, labour hours and kilograms of materials; this covers all the activities defined in the project budget, and in this way, the data necessary for the calculation of the HE of the rehabilitation of buildings is obtained. The resource quantification bank is the calculation engine of the evaluation model developed. The great diversity of activities included in the cost assessment and the resource quantification bank allow the model to be applied to any residential building type. Finally, the model is applied to a real case study, the rehabilitation of the "Barriada RENFE" building, located in the Macarena District of the city of Seville, Spain. 6 2.1. Economic assessment: rehabilitation cost database The aim of this work is to make the comparison between the rehabilitation of a building with serious pathological damage, and its demolition and rebuilding. This comparison is performed in terms of the economic and environmental impact (Alba-Rodríguez, 2016). In order to obtain the economic evaluation, this study follows the systematic classification of the Andalusia Construction Cost Database (ACCD): a consolidated classification model that is mandatory for public project budgets in Andalusia. Its system for management and classification of work units is flexible and adaptable, thereby enabling the incorporation of new costs corresponding to the rehabilitation of buildings (Marrero and Ramirez‐De‐Arellano, 2010). Due to the special circumstances of rehabilitation work, it is necessary to create complex costs (CC), as shown in Figure 1. To define the tasks in each CC, simple costs (SC) from the ACCD are used. These consist of auxiliary costs (AC) and basic costs (BC), which are classified into materials, manpower and machinery. CC are supplemented with AC to include the increase in manpower and materials required due to the greater difficulty of rehabilitation work, as compared to new construction. Improvements in the thermal characteristics of the building envelope, and in the energy efficiency of the installations, are included in the rehabilitation costs developed in this work. Once the economic cost of the building rehabilitation has been obtained, the comparison with the data for the demolition and new construction can be carried out. To determine the economic cost of the demolition and new construction, data from previous studies is used (González-Vallejo et al., 2015a), and it is assumed that the new building will have the same floor area of the existing building, but will be updated to meet current regulations and with materials of average quality. In Gonzalez-Vallejo´s work, 94 different social housing projects in Andalusia, Spain are analysed using the ecological footprint indicator. The projects are classified by: number of floors, structure type, underground parking, roof type, and foundation and the average project quantities are determined per floor area. All construction projects must meet the Spanish Technical Constuction Code, and the solutions are those commonly employed in social housing. 7 Figure 1. Simplified diagram of a complex cost (CC) 2.2. Environmental impact assessment: Ecological Footprint The EF indicator is employed for the environmental assessment of the building rehabilitation project. The evaluation is performed from the project budget perspective, since cost control is widely applied in construction projects. Project costs are normally divided into direct and indirect costs, the latter being those non-attributable to a specific task, but instead to the whole construction process. The same classification is proposed for the environmental evaluation (Figure 2, first level). In the third level of Figure 2, three resources are determined through indirect costs: electricity, water consumption, and built-up land. Electricity is consumed by electric tools and lighting, and domestic water is consumed in temporary meeting and dressing rooms built at the construction site. All these aspects depend on the general characteristics of the project. The same occurs with the water consumption on site (Freire and Marrero, 2014). The estate where the construction itself is built is considered a consumption of land, and consequently has an associated footprint. Regarding the EF associated to direct costs, the three main impact sources obtained through the project’s bill of quantities are identified as manpower, construction materials, and machinery. Manpower causes an environmental impact through the workers’ food consumption and the generation of municipal solid waste (MSW) during their working hours. Construction materials emit CO2 during their manufacturing process and require transport (fuel consumption) for 8 delivery to the construction site. Moreover, construction and demolition waste (CDW) is generated through demolition processes or the loss rate from the use of new construction materials. Finally, the third resource determined from the project budget is machinery, whose level of CO2 emissions is obtained through their fuel or electricity consumption, depending on their power source. The impacts caused by the sources above are transformed through conversion and productivity factors into world-average hectares (wha), and finally through equivalence factors into global equivalent hectares (gha). The EF indicator divides impacts into six different land categories, represented in the bottom level of Figure 2: cropland, grazing land, fishing grounds, CO2 absorption land, forest land, and built-up land. These six categories can be added together to form the Total Ecological Footprint. In the following sections, the calculation methodology for each element is explained in detail, following the guidelines established by Solís-Guzmán et al. (2013) and González-Vallejo et al. (2015a). Alterations of operational costs derived from the rehabilitation or reconstruction of the building with constructive solutions of a more efficient nature, as well as the associated environmental impact, are also assessed in order to be included in the comparison of these two options, as suggested by de Jonge (2005). 9 Figure 2. Methodological flowchart. 2.2.1. Electricity The theoretical consumption of electricity is based on the indirect costs of the project. Each concept of the indirect costs is transformed into useful data to calculate the EF (effective annual hours of manpower, fuel consumption by machinery, consumption of water and electricity on the worksite, etc.). In Table 1, the indirect costs due to electricity consumption are shown (Freire Guerrero and Marrero, 2015). Table 1. Determination of the electricity consumption on the construction site Code Concept Unit Power consumption Total Power Machinery, equipment and tools (per month) month kWh/month kWh Concrete mixer 8.27 101.67 1,235.25 Ancillary and complementary facilities m2 kWh/m2 kWh Worksite Offices 20.50 191.02 3,915.91 Toilets and changing rooms 6.00 191.02 1,146.12 Dining room 3.60 191.02 687.67 Storage rooms 35 191.02 6,685.70 Other electrical consumption m2 kWh/m2 kWh Lighting of the construction site (plot) 876.0 2.60 2,277.60 Total 15,948.24 The emission factor corresponding to the electric mix in Spain (REE, 2014), as well as a reduction of 28% in the emissions due to the carbon uptake in oceans (Borucke et al., 2013; GFN, 2014) are included in the calculations of the EF of electricity consumption (equation 1, Table 5) (Martínez- Rocamora et al., 2016a). 2.2.2. Water consumption The EF of water consumption is calculated through the energy necessary to bring it to the point of consumption, including previous and subsequent treatments. This energy intensity (EI) is obtained from the supply company (EMASESA, 2005), and is assumed to be electric energy (equation 2, Table 5). 2.2.3. Built-up land The area used by the urbanization and the building under study produces a direct footprint on the environment which corresponds to the area of the housing site, lot size, which would be equal 16 A new air-conditioning installation consisting of a multi-split system with an inverter and heat pump is proposed. The electrical installation is completely replaced (circuits, wiring, switches, light points and sockets, ground wires). The plumbing (pipes, drains and sanitary equipment) and the DHW production system are replaced with a community system with solar thermal panels, individual accumulators and auxiliary systems for each dwelling. In order to complete the improvement of the energy efficiency of the envelope and to meet the requirements of the CTE-DB-HE1 (Spain MPW, 2013), the original exterior windows are replaced with lightweight aluminium frames with thermal breaks and double low-emissive glass (6 mm thick and 12 mm dehydrated air chamber), thereby reducing thermal and acoustic transmission. All the activities are transformed into CC in Table 6. The codes are as defined in ACCD. Table 6. List of CC for the rehabilitation of the RENFE residential complex CODE unit SHORT DESCRIPTION 03. FOUNDATIONS 03RZQ00001 m Linear foundation underpinning w/micropiles on site, w/steel jacket ø 60 mm and 27.00 m depth 04. SEWERS 04RAS50010 u Replacement of sewer manhole 63x63 cm and 1 m depth 04RES50010 m Replacement of sewage collector with polyethylene tube 200 mm diameter 04RVS90010 m Replacement of polypropylene soundproof downpipe, mixed network, external and internal 05. STRUCTURES 05RFU80001 m2 Compression layer reinforcement in unidirectional floor 06. MASONRY 06RLR05013 m2 Repair of cracks in external load-bearing wall and external energy retrofitting from the exterior with EPS 80mm. Continuous coating 06RLS70011 m2 Replacement of interior load-bearing wall 06RLR70022 m2 Repair of fissures with fibreglass mesh in brick partitions 07. ROOFTOP 07RHR00152 m2 Energy retrofitting of inverted rooftop, EPDM layer 1.2 mm and EPS 80 mm 08. INSTALLATIONS 08RCS10100 u Multi-split 3x1 parted hot/cold climate system 08RES20100 u Replacement of electric installation 08RES20050 m Grounding installation 08RFS30100 u Replacement of plumbing installation 08RFS30090 u Replacement of DHW production system with community system with solar panels, accumulator and individual auxiliary system 11. CARPENTRY, SAFETY AND PROTECTION ELEMENTS 11RBL10010 m2 100% Recovery of protection bars in windows of ground floor 11RVS12022 m2 Thermal break aluminium windows/low emissive/type III, manual aluminium blinds 17 3.3.2. Energy simulation An energy simulation has been carried out in three different scenarios: the initial state, before the construction failure; the rehabilitation state, once the actions defined above have been performed; and a new construction scenario. It is necessary to point out that the first constructive solution simulated in the case of new construction corresponds to the minimum requirements set out in CTE DB-HE in its 2006 version (Spain MPW, 2006), which was active when the incident took place (2010), whereby the energy rating for the new building in this case is D. A second case of new construction is carried out in accordance with the minimum requirements set out in CTE DB-HE in its more recent 2013 version (Spain MPW, 2013), which achieves B as its energy rating. With the rehabilitation described, the energy efficiency of the building is also improved to a B rating. Table 7. Comparison of energy efficiency: rehabilitation vs. new building Transmittance U (W/m2K) Nominal Performance (COP/EER/%) Global CO2 Emissions (kgCO2/m2·yr) Energy Efficiency Rating Energy Consumption (kWh/m2)·yr Final Energy Consumption (kWh/m2)· 25 years INITIAL SCENARIO Envelope 2.112 … 26.27 E 89.70 2,242.50 Rooftop 1.107 … Windows 5.700 … Heating/DHW system … 1.0/87% REHABILITATION SCENARIO (Energy retrofitting included) Envelope 0.383 … 6.64 B 21.01 525.25 Inverted rooftop 0.332 … Windows 2.220 … Heating/Air C./DHW … 4.4/4.2/95% NEW CONSTRUCTION SCENARIO In accordance with CTE DB-HE (2006) Envelope 1.720 … 14.96 D 51.14 1,278.50 Inverted rooftop 0.570 … Windows 3.540 … Heating/Air C./DHW … 1.8/2.2/87% In accordance with CTE DB-HE (2013) Envelope 0.380 … 6.46 B 20.44 511.00 Inverted rooftop 0.460 … Windows 1.800 … Heating/Air C./DHW … 4.4/4.2/99% 18 As can be seen in the last column of Table 7, the final energy consumption period has been set to 25 years (without restatement), which is the estimated time before another intervention would take place. The economic impact is also obtained using the same period (Table 8). Table 8. Economic and environmental impact of energy consumption in a 25-year timespan for the three scenarios Scenario Energy consumption (kWh/m2) 25 years Cost (€/m2) Fossil EF (gha/m2) % INITIAL 2,242.50 316.27 0.141 100.00% REHABILITATION 525.25 74.08 0.033 23.42% NEW CONSTRUCTION In accordance with CTE DB-HE (2006) 1,278.50 180.31 0.080 57.01% In accordance with CTE DB-HE (2013) 511.00 72.02 0.032 22.79% 4. Results 4.1. Economic impact by chapters, rehabilitation vs. new construction A budget summary given in chapters for the rehabilitation and for the new construction is shown in Table 9. In both cases, most of the economic weight falls on the installations chapter, which represents 33.17% of the cost of rehabilitation and 40.81% or 40.67% of that of new construction (depending on the scenario). However, the subsequent chapter in order of economic importance varies between the two cases. In the case of rehabilitation, it is the masonry chapter, with 26.04%; in new construction, it is the coatings chapter that represents 12.45% or 12.41% (depending on the scenario). Since the rehabilitation budget has been made with CC, all coatings have been included in its masonry chapter and hence the difference in the order of economic importance of the chapters. Structures represent the next chapter of economic importance in the new constructions with 11.96% or 11.92%; this figure stands at only 1.92% in rehabilitation, since it results from the reuse of the existing structures by performing tasks of repair and/or consolidation. The high cost of the foundations chapter is justified by the size of the underpinning due to the great depth of the resistant layer of soil (Ferreira-Sánchez et al., 2016). 19 Table 9. Summary by chapters of the TPC of rehabilitation vs. new construction REHABILITATION NEW CONSTRUCTION Under CTE DB-HE (2006) Under CTE DB-HE (2013) CHAPTERS TPC (€) % TPC (€) % TPC (€) % Excavations … … 5,751.98 0.30 5,751.98 0.30 Foundations 186,131.06 12.74 91,783.12 4.76 91,783.12 4.75 Sewers 63,223.62 4.33 17,986.33 0.93 17,986.33 0.93 Structures 28,002.13 1.92 230,506.80 11.96 230,506.80 11.92 Masonry 380,542.43 26.04 216,585.88 11.24 216,585.88 11.20 Rooftops 87,610.05 6.00 74,302.38 3.86 47,217.02 2.44 Installations 484,636.53 33.17 786,581.46 40.81 786,581.46 40.67 Insulation … … 19,677.10 1.02 24,955.49 1.29 Coatings … … 239,937.92 12.45 239,937.92 12.41 Carpentry 197,518.86 13.52 149,862.67 7.78 167,550.36 8.66 Glass … … 10,324.02 0.54 21,027.41 1.09 Paint … … 73,072.24 3.79 73,072.24 3.78 Waste management 33,572.56 2.30 11,018.40 0.57 11,066.52 0.57 TOTAL 1,461,237.24 100.00 1,927,390.32 100.00 1,934,022.55 100.00 4.2. Environmental impact of rehabilitation 4.2.1. Electricity and water EF The EF results produced by the electricity and water consumption are obtained by applying equations 1 and 2, respectively, to the total amounts consumed on site. These consumptions come from the general data of the project, quantified indirectly depending on the floor area and the duration of the work by applying average consumptions established for the building type. Table 10. Fossil EF of electricity and water consumption EF of electricity and water consumption (Indirect costs) Electricity consumption (kWh) Worksite offices 12,435.40 Worksite lighting and tests of installations 2,277.60 Total electricity consumption 14,713.00 Fossil EF of electricity (gha) 0.922 Total water consumption 619.51 Fossil EF of water (gha) 0.016 4.2.2. Built-up land EF In order to determine the built-up land EF, the total land area must be obtained. To this end, the floor area occupied direct by the building is calculated, giving a total area of 875.67 m2. By means of an equivalence factor of 2.51 gha/ha (agricultural land), the EF of built-up land can be calculated as 0.202 gha. 20 4.2.3. Manpower EF In order to calculate the EF of food consumption, the total number of manpower hours worked during the entire project is calculated, which is obtained from the project’s bill of quantities and its direct and indirect costs (Table 11). Table 11. Manpower hours (rehabilitation activities) Manpower unit Quantity Construction personnel h 33,612.15 Machinery operators h 2,567.28 Manpower as part of the indirect cost of the project h 11,211.28 Total working hours 47,390.71 The EF produced by manpower concludes with the calculation of the impact of MSW generated by the workers. To this end, equation 5 (Table 5) from Section 2.2.4 is used. This result is expressed in fossil EF, since it represents the energy necessary for the management of the MSW generated (Table 12). Table 12. EFfood and EFMSW of workers (rehabilitation work) EF of manpower (rehabilitation) Fossil EF (gha) Pasture EF (gha) Sea EF (gha) Crops EF (gha) FOOD 1.08 2.17 3.41 7.95 Food EF (gha) 14.62 MSW 0.225 … … … EFMSW (gha) 0.225 4.2.4. Construction materials EF The results of the fossil EF of the main families of construction materials are shown in Table 13, which represent 93% of the total weight of materials consumed in the rehabilitation. For the purpose of comparison, materials for the new construction are shown in parallel, which represent 97% of the total weight and 93% of emissions. 21 Table 13. Embodied energy in the most representative construction materials in the project REHABILITATION Material Total Quantity (t) % Weight Total Emissions (tCO2) % Total EF CEMENT 315.24 21.77 239.92 41.14 STEEL 43.61 3.01 103.28 17.71 PAINT 56.85 3.90 95.80 16.43 CERAMIC 106.43 7.35 36.17 6.20 ALUMINIUM 3.43 0.24 34.31 5.88 LIME 29.82 2.06 22.34 3.83 CONCRETE 85.96 5.94 16.81 2.88 SAND 704.99 48.68 1.38 0.24 WOOD 3.13 0.22 -21.26 -3.65 ∑ per family 1,349.46 93.00 528,75 91.00 In the rehabilitation work, the material with the highest CO2 emissions is cement, with 41%, and this material is the second highest in terms of weight (22%). This is due to the necessity of cement in the underpinning of foundations, given the low bearing quality of soil. The material with the next highest CO2 emissions is steel, with 18%, despite not being the material with the next greatest weight within the work. Regarding ceramic materials, due to actions performed on the structure based on load-bearing brick walls, this is a material with considerable representation (7%) and also notable emissions (6%). Comparing these results with those obtained for new construction, it can be seen that, in this case, the results are dominated by concrete both in weight (62%) and environmental impact (36%), and this dominance can be explained by the needs for new structural elements of the building, which in the case of rehabilitation are recovered or reused with the consequent saving of materials. 4.2.5. Machinery EF The EF of each piece of machinery is calculated in Table 14 through its engine type, hours used, power, and fuel consumption. When observing the EF results obtained, the higher representativeness of fuel machinery against electrical machinery must be borne in mind, and more specifically within this group, the telescopic lifting platform, which represents 43% (7.67 gha) of the total fossil EF of machinery. The fact that this high proportion of the fossil EF is not produced by the machinery with more hours of use proves that the fossil EF generated is directly related to the performance of the machinery used. 22 Table 14. Total EF (gha) of fossil combustion machinery Code Machinery Quantity (h) Cost (€) Consumption Consumption EF (ha) Fossil EF (gha) FUEL (l) Loader 54.15 1,292.59 1,299.63 0.678 0.85 Backhoe 1.04 36.28 13.90 0.007 0.01 Dump truck 25.27 646.99 1,263.66 0.659 0.83 Mechanical tilt truck 15.16 55.33 272.85 0.142 0.18 Micro-pile drilling equipment 886.39 248,190.5 5 10,104.90 5.269 6.64 Drilling eq. w/ diamond crown 20.21 770.85 230.41 0.120 0.15 Drilling eq. w/ hole hammer 90.47 2,656.15 1,031.34 0.538 0.68 Telescopic platform 729.55 5,471.65 11,672.85 6.087 7.67 TOTAL 1,822.2 4 259,120.4 0 25,889.54 13.500 17.01 ELECTRIC (kW) Two-hammer Compressors 609.16 3,868.13 12,183.10 0.61 0.76 Vibrator 25.31 38.22 12.65 0.001 0.001 Concrete mixers 840.30 3,600.11 1,235.25 0.06 0.08 TOTAL 1,474.7 7 7,506.46 13,431.00 0.67 0.84 TOTAL EF fósil 14.17 17.85 4.2.6. Total EF From the partial EFs, the fossil EF from the energy consumption is prominent at 88% of the total EF (177.23 gha). Construction materials produce 88% of the total fossil EF (156.73 gha). Although they are less significant, the remaining partial footprints must not be underestimated, since they add up to 11.65% of the total EF. Analysing the EF in terms of impact source, construction materials stand out, since they account for 82.93% of the total EF, followed by fuel machinery with 8.48%, and food consumption by manpower with 7.29% (both workers and machine operators). The remaining impacts (electricity, CDW, MSW, water, and built-up surface) together account for 1.29% of the total EF. 23 Figure 5. Percentages of partial EFs in terms of impact source. Rehabilitation of the RENFE complex 4.3. Comparison: rehabilitation vs. demolition and new construction An economic and environmental comparison between rehabilitation and demolition and new construction is shown in Table 15, regarding the outcomes of the three different processes involved. For the comparison to be complete, the results obtained in terms of EF are shown, also expressed in global hectares per m2. Table 15. Economic and environmental comparison: rehabilitation vs. demolition and new construction COMPARISON FOR SUBCATEGORIES Demolition New construction Demolition + new construction Rehabilitation Electricity (gha) 1.578 2.356 3.934 0.922 Water consumption EF (gha) … 0.018 0.018 0.016 Built-up land EF (gha) … 0.202 0.202 0.202 Manpower EF (gha) 2.490 18.975 21.465 14.85 Construction materials (gha) … 543.104 543.104 166.76 Machinery 0.349 23.760 24.109 17.85 FINAL COMPARISON Demolition New construction Demolition + New construction (2006) Demolition + New construction (2013) Rehabilitation CTE DB-HE (2006) CTE DB-HE (2013) TPC (€) 85,457.17 1,927,390.32 1,934,022.55 2,012,847.49 2,019,479.72 1,602,100.51 Total EF (gha) 4.42 467.82 588.49 473.88 592.83 200.6 Total EF (gha/m2) 0.002 0.134 0.168 0.136 0.169 0.06 Materials 82.93% Food 7.29% Fuel 8.48% Rest of impacts 1.29% 24 It can be observed how the TPC of rehabilitation is only 21% lower than that of demolition and new construction, while the environmental impact is between 58% and 68% lower in the case of rehabilitation. With these results, the relevance of this feasibility model is proven, since it shows that the economic aspect is not the only factor to be taken into account in the feasibility analysis. Environmental aspects must also be considered, given the results obtained. 4.4. Energy improvement comparison: rehabilitation vs. new building To conclude, one last comparison (Figure 6) is given between the EF generated by energy consumption during the use phase of the building (a period of 25 years is considered) and the total EF generated by the rehabilitation work, and demolition and new construction (Table 7), including the energy consumption of the rehabilitated state and that of new construction in the same timespan. Figure 6. Environmental impact comparison: total EF of energy consumption and work execution In the event of not having proposed any actions to improve the energy efficiency of the building and thus limiting the intervention to mere correction of pathologies, the impact caused by energy consumption during the period analysed would be 0.141 gha/m2 (initial state). The EF of energy consumption caused by the rehabilitated state in the same period (0.033 gha/m2) and the impact caused by the rehabilitation work (0.060 gha/m2) together give a total of 0.093 gha/m2. This is almost 66% less impact than that of new construction. However, despite the significant reduction in energy consumption compared to that of the original building, the process of demolition and 0.033 0.032 0.080 0.141 0.060 0.168 0.134 Rehabilitated state New construction CTE DB-HE (2013) New construction CTE DB-HE (2006) Initial state EF(gha/m2): energy consumption (25 years) EF(gha/m2) : work execution 0.214 0.200 0.093 25 new construction poses such a high impact (0.214 gha/m2 and 0.200 gha/m2, depending on the CTE DB-HE applied) that this kind of intervention remains unjustified. These results prove the importance of energy retrofitting when rehabilitating a building, since excellent results regarding economic and environmental impacts can be achieved for the timespan analysed. 5. Conclusions As stated at the beginning of this paper, the main objective of the study is to develop a model that allows a comprehensive analysis of the economic and environmental costs of rehabilitating buildings. This aim is achieved through the use of the systematic classification from the ACCD, and hence any technician familiar with cost databases can easily understand and apply the proposed methodology. EF assessment is applied for the first time in building rehabilitation through the development of a robust and replicable model that allows decision-making from a double economic and ecological perspective. From the application of the model on the case study, a series of results are obtained which validate the evaluation model. These results provide a global image, both economic and environmental, of the rehabilitation of the RENFE building: - The analysis of partial EFs of rehabilitation reveals that the embodied energy of manufacturing, transport and installation of the materials used in this process cause 82.93% of the total EF. Cement (41.14%) and steel (17.71%) particularly stand out in terms of CO2 emissions due to the execution of the foundation underpinning. - The impact on the TPC of the energy improvement actions is justified by the comparative analysis through energy simulations of the rehabilitated building against its initial state, for a 25-year span. Through this analysis it can be concluded that the actions performed on energy improvement reduce both the economic and environmental impact to 66 % of that of the initial state. - From the comparison relating the results of rehabilitation with demolition and new construction, it is concluded that the TPC of rehabilitation is 21.31% lower than the budget of demolition and new construction. On the other hand, the environmental impact in terms of EF is 58% and 68% lower (depending on the CTE DB-HE applied) in the