A Sustainability Assessment of Industrialised Housing Construction Using the MIVES (Modelo Integrado de Valor para una Evaluación Sostenible)-Based Multicriteria Decision-Making Method

Abstract

Recently, the world population surpassed 8000 million people. Providing housing for such a large population poses a great challenge for the building industry and its impact on the planet. The rise in the urban population leads to greater impacts not only on the environment but also on economies and societies. Consequently, reducing these externalities is mandatory to preserve the welfare of the world. One way of optimising the economic cost of housing is through industrialising the production of housing. However, a balance between housing optimisation and the management of the social/environmental impacts has not yet been achieved. In order to bridge this gap, in this study, a holistic evaluation of several housing systems was performed using the MIVES (“Modelo Integrado de Valor para una Evaluación Sostenible”)-based multicriteria decision-making method (MCDM method). Moreover, the obtained results were compared, showing which industrialised building technique might enhance the sustainability of housing production.

1. Introduction

Since the Industrial Revolution at the beginning of the 18th century, the global population has risen exponentially. Although the growth rate is steadily decreasing, this rise will continue at least into the near future. Additionally, life expectancy has been increasing worldwide since the 1500s and is now higher than ever. Consequently, providing proper housing for a population greater than eight billion people poses not only a remarkable technical challenge but also a significant risk to nature due to the environmental impact of construction [1,2,3].

One of the main aspects configuring the wellbeing of any population is the characteristics of its housing, and there are studies showing that the quality of housing is connected to the population’s life expectancy [4,5]. Housing has been constructed using materials such as wood, steel, and reinforced concrete in developed countries to provide a safe and healthy environment. However, in recent times, these characteristics have ceased to be the only ones demanded by society. Due to the environmental impacts generated by the building industry, it has become crucial to manufacture housing with proper characteristics while ensuring limited resource consumption during construction and maintenance, as well as ensuring durability [6,7,8]. It should be kept in mind that most construction comprises reinforced concrete, and currently, cement production is responsible for around 8% of the total CO₂ emissions worldwide [9,10].

In light of the burgeoning population and the resultant strain on the environment, especially in developing countries, durable, economical, and sustainable housing is required not only to provide proper living conditions but also to minimise the externalities of cities on nature. Prefabrication, modular construction, and other innovative techniques not only expedite construction processes but also contribute to minimising the environmental impact [6,11,12]. All of these methods could be referred to as industrialised construction. Industrialised construction refers to a systematic approach to building structures and construction that emphasises efficiency, precision, and off-site processes [13]. Some of the main possibilities available with industrialised construction encompass off-site prefabrication, assembly-line production, the use of advanced materials, modular construction, and potential reductions in economic costs and environmental impact [13]. Recently, several industrialised housing construction systems such as MDR modular housing have proven to be economically viable; however, no assessment of their environmental impact has been carried out. Moreover, there has been no evaluation of the variation in the impact that can be achieved when wooden prefabricated systems or MDR modular housing are used as substitutes for traditional building methods.

The concept of sustainability gained prominence in 1987 through the Brundtland Report. This report emphasised the adverse environmental impacts of economic growth and globalisation and sought solutions to the issues arising from industrialisation and population growth. Many of these challenges necessitate the promotion of sustainable development [14] involving a commitment to social progress, environmental equilibrium, and economic growth. Achieving this commitment requires active participation from individuals, businesses, administrations, and countries on a global scale [15,16].

The present global landscape calls for a substantial shift to align with emerging governmental and global policies [17]. Furthermore, the increasing prioritisation of sustainability in government agendas and the heightened public awareness surrounding sustainability issues exert pressure to address the juxtaposition of sustainability with traditional financial objectives [18,19]. This evolving scenario underscores the imperative for a comprehensive and transformative approach to address the challenges posed by the intersection of economic goals and sustainable practices.

There is no single way to assess the sustainability of a construction project. There are a wide variety of methods that can be used, according to the specific building or construction being evaluated. These diverse methods not only provide owners with a better public image but also help policymakers increase the requirements set for a building or construction [20,21,22,23]. Given the numerous methods available, some studies have examined the influence of choosing different environmental schemes, and there is no unanimous opinion on which aspects are optimal. Notable differences in evaluations can appear [24,25,26,27]. Some of the most employed methods for buildings are the LEED (Leadership in Energy and Environmental Design) method [28], the BREEAM (Building Research Establishment Environmental Assessment Method) approach [29], or the CASBEE (Comprehensive Assessment System for Built Environment Efficiency) method [30]. These methods share similarities, as they are comprehensive sustainability assessment tools with point-based rating systems, multifaceted categories, and global applicability and are subject to continuous improvement. However, each method is tailored to regional particularities and needs. Additionally, although these methods were primarily designed for buildings, they have been adapted to evaluate urban planning, land use, neighbourhoods, infrastructure, transport, and even communities. In this context, MIVES, which stands for “Modelo Integrado de Valor para una Evaluación Sostenible”, is a sustainability assessment MCDM method that was designed to cover all aspects of the building industry, ranging from buildings to bridges, tunnels, and even risk definitions [31,32,33,34,35,36]; however, its applicability to construction methods remains to be determined.

Based on the previous arguments, the purpose of this article is to compare the sustainability index scores of three housing construction methods using the MIVES methodology. The aim is to show that industrialised systems are not only more environmentally friendly but also have a significantly higher overall sustainability index than traditional systems. In addition, the suitability of MIVES as a tool for assessing the impact of construction methods is analysed. This is a completely novel approach, as it considers not only a determined construction but a methodology. This might have influence in relation to reducing CO₂ emissions if the conclusions of this study are considered by construction companies. After the work performed, it can be stated that MIVES integrates economic, social, and environmental parameters, providing sound conclusions regarding the sustainability with regard to construction systems. The MDR system is the most favourable economically, while the timber construction method stands out as the best environmentally. In addition, the MDR system showed a reduced social impact compared to both the timber and traditional methods, with the traditional system performing the worst overall.

2. Description of MIVES

Although the awareness regarding the damage that humans inflict on nature dates back several decades, there is not a unique method in the building industry to determine the deleterious effects. The absence of a universal tool can be explained by the extreme complexity of assessing the environmental impact, taking into account economic and social aspects, ethical and political issues, local culture, and technological and scientific matters [37]. Up to now, several of the most successful approaches have been multicriteria decision-making tools (MCDMs) [38,39,40,41,42], whose main approach is to divide the problems into smaller portions that can be analysed in a simpler way. It should be mentioned that these methodologies are not limited to determining the sustainability of a given case but can be applied to a wide variety of situations.

One of the several MCDMs that have been created is termed “Modelo Integrado de Valor para una Evaluación Sostenible” commonly known as MIVES. Like any other MCDM method, MIVES aggregates the evaluations carried out at different levels but also uses utility functions and weights in order to adjust the importance of every aspect involved. The determination of these utility functions and weights are based on the opinions of experts. It should be mentioned that the functions that are employed in MIVES can have any shape that might be suitable for analysing the parameter as long as they range from 0 to 1. For example, concave, convex, linear, or multi-linear shapes among others are accepted. Due to this multi-level scheme, MIVES can be considered as a versatile tool capable of assessing the sustainability not only of materials or structures but also of determining the effectiveness of methods to control the uncertainty and risk of climate change or flooding among other matters [43,44,45,46,47].

The relevance of MIVES has increased since its creation in 2008, and currently, there are almost 60 research papers published in indexed journals [48]. Nevertheless, there are still some fields, such as the assessment and comparison of the sustainability of industrialised construction processes, where its suitability has not been fully proven. Consequently, one of the main objectives of this paper is to check the applicability of MIVES to this new field.

3. Description of the Housing Typology and the Compared Building Methods

All the methods analysed were applied to a house suitable for three people located in the suburbs of a Spanish city. The house comprised three bedrooms, two bathrooms, a living room, and a kitchen. The total surface of the house was approximately around 120 square meters. The materials suppliers, both of the timber and concrete, were less than 100 km from the house location. Regarding the design criteria, the Spanish recommendation Código Técnico de la Edificación (CTE) was selected. This regulation establishes the structural, safety, and habitability conditions that the house should meet.

The methods analysed were the following: traditional construction and industrialised construction using timber and an MDR system. The traditional system is mainly defined by onsite construction techniques with a low degree of technification. The typology chosen was a hyperstatic-concrete structure with isolated footings. The rest of the structure was composed of reinforced concrete pillars and either a hollow-core concrete slab or unidirectional floors made with hollow ceramic blocks and reinforced concrete. In such cases, the loads of the floors are transmitted to the reinforced concrete beams, and these beams transfer the loads to the pillars. The façades were built with bricks and mortar with plaster layers in the interior. The roof was slanted with ceramic tiles that were supported by a unidirectional-concrete floor. In Figure 1, a sketch of some of the characteristics of the traditional construction method can be seen.

The industrialised construction method using timber was chosen due to the previous studies that emphasized that the use of timber in the construction of houses reduced the environmental impact [49,50]. Some of the characteristics of the system can be seen in Figure 2. The reduction in the impact is based on the use of sustainable sources of wood that might be awarded an FSC certification, which ensures that the forestry development is carried out with regard to biodiversity and the local population while maintaining profits. In previous research [49,50], it was concluded that the use of cross-laminated timber (CLT) was the most sustainable construction method among those studied, as compared to a beam-and-column system and a modular system. That study was conducted considering a four-story building, which contained 16 apartments with living areas between 42 and 78 m². In order to adapt the values of the study to our research, the assessment of each section was averaged. The CLT method is composed of walls and flooring, and even the interior walls are laminated timber. The exterior walls in the CLT method comprise a ventilated façade of plaster, wood lath, stone wool, and gypsum. The roof section comprises asphalt sheeting, wood panels, timber trusses, stone wool, plastic films, and gypsum boards. The floors are composed of laminated wood boards, expanded polyethylene, CLT, glulam beams, glulam flanges, stone wool, wood panels, and gypsum boards. Finally, the foundation is made with a reinforced concrete slab, extruded polystyrene, and crushed stone.

The third construction method chosen in this study is called MDR. This system is a patented modular-based construction method. The method is based on using concrete-compact modules that can be stacked and joined together in order to form houses with several typologies. Its main advantage is that each module is completed in the factory and is connected to the adjacent ones onsite. Each module includes all the installations such as electricity, gas, air conditioning, water supply, and sanitation. Moreover, the module also incorporates both the interior and exterior finishes. According to the manufacturer, although the modules are made of reinforced concrete, the quality and energy efficiency of the house derived from the construction process, together with the durability of the materials, confer on the construction method a remarkably low environmental impact. Moreover, the onsite labour decreases the impact on the location where the house is built is notably reduced. The system has some other advantages such as the low qualification requirements of the workforce for onsite labour and the limited number of workers needed. From the structural point of view, the modules are monolithic elements with two slabs (the floor and the ceiling), which are connected with four perimeter walls. A section view of the MDR system can be seen in Figure 3.

4. Application of MIVES to the Three Building Methods

Based on the three alternatives shown in Section 3,

Table 1. Requirements, criteria, indicators, and weights. Source: self-developed based on similar studies [51,52,53].

Requirement	(Weight R)	Criteria	(Weight C)	Indicators	(Weight I)
E1. Economic	50%	C1 Costs. Direct + indirect	50%	I1 Direct costs	85%
				I2 Indirect costs. Time (visits, leases, etc.)	5%
				I3 Other indirect costs (financial and insurance)	10%
		C2 Quality	10%	I4 Costs of non-conformity	100%
		C3 Life span	30%	I5 Service costs. Maintenance, energy, and refurbishment	80%
				I6 Resilience. Risk of disasters × reconstruction costs + lack of use	20%
		C4 Demolition	10%	I7 Demolition costs	50%
				I8 Possibility of reusing materials	50%
E2. Environmental	25%	C5 Consumption of materials during manufacturing and construction (potential global warming)	35%	I9 Reinforced concrete	35%
				I10 Mortar	10%
				I11 Wood	5%
				I12 Ceramics	20%
				I13 Other materials	30%
		C6 Consumption of materials in maintenance and service (potential global warming)	5%	I9 Reinforced concrete	35%
				I10 Mortar	10%
				I11 Wood	5%
				I12 Ceramics	20%
				I13 Other materials	30%
		C7 Emissions during construction. Manufacturing + transportation + assembling	25%	I14 Total residue	100%
		C8 Emissions in maintenance and service	5%	I14 Total residue	100%
		C9 Energy	30%	I15 Energy incorporated	25%
				I16 Energy consumed in construction	5%
				I17 Energy in maintenance and service	70%
E3. Social	25%	C10 Design, construction, and maintenance	20%	I18 Comfort during construction (thermal, acoustic, and protection of workers)	40%
				I19 Acoustic and air pollution during construction	15%
				I20 Interactions with the environment during construction. Duration of the impact × importance of the impact. (Traffic, adjacent properties, street closures, etc.)	15%
				I19 Acoustic and air pollution during maintenance	15%
				I20 Interactions with the environment during maintenance. Duration of the impact × importance of the impact. (Traffic, adjacent properties, street closures, etc.)	15%
		C11 Risks during construction and service	40%	I21 Health and safety during construction	85%
				I22 Subsidiary risks of the promoter during construction	10%
				I23 Security	5%
		C12 Comfort during use	40%	I24 Thermal comfort	25%
				I25 Acoustic comfort	25%
				I26 General comfort	25%
				I27 Effects on third parties	25%

was developed. In this table, several requirements, parameters, and criteria are described. It should be underlined that the weight of each of the fields that appear in Table 1 was determined before establishing the values of these fields with regard to a specific construction alternative. Consequently, the final purpose of assessing the sustainability of each building method was completely objective and unbiased. Another point that should be considered is that, due to the absence of data regarding some parameters, several references were consulted [51,52,53]. In the following paragraphs, the values that appear in Table 1 are justified.

With respect to the economic costs (C1), several studies have highlighted that for a middle-class family living in Spain, economic costs play a crucial role in determining the suitability of a particular type of house. Consequently, the overall weight assigned to these costs was set at 50%. This high value can be divided into direct costs (I1) and indirect costs (I2 and I3). I1 represents the total amount of money the family needs to purchase the house. Indirect costs, represented by I2, include expenses incurred from the time the decision to buy the house is made to when the house is ready for occupancy. This period might involve leasing a temporary living facility during the house’s construction and transportation costs if the house is located in a different city. Financial and insurance costs are included in I3. This is an important parameter, because the cost of house insurance is related to the house’s characteristics. Another category of economic costs, termed C2, includes those related to non-conformities concerning construction quality, represented by parameter I4. Costs related to the house’s lifespan are summarized in C3. This category is further divided into two components: I5, which covers maintenance, refurbishment, and operational costs, and I6, which estimates the house’s resilience to extraordinary events. I6 also includes the associated repair costs after such events and the cost of temporary housing during the repair period. It should be noted that the energy consumption is included in I5, and consequently, the uncertainty associated with rising energy costs in the coming years is also accounted for in I5. Lastly, C4 addresses the dismantling of the house once its lifespan has expired or even during its lifetime. C4 considers not only dismantling costs (I7) but also the potential for recycling the materials (I8).

The building industry, which includes both infrastructure and buildings, is responsible for consuming approximately 60% of the materials extracted from the lithosphere. Of these materials, 40% are utilized in buildings, accounting for around 24% of the total materials used annually. When these numbers are converted into CO₂ emissions, they represent between 30 and 40% of the global CO₂ emissions [54]. Apart from that, the CO₂ emissions related to the transportation, construction, and installation of a building involve significant amounts of energy. A detailed breakdown of these impacts is provided in the parameters ranging from C5 to C9. While the consumption of materials during the construction phase is addressed in C5, those used in maintenance and service are detailed in C6. These two criteria include the CO₂ generated during the extraction of materials, production processes, transportation, and use (C5), as well as during maintenance and service (C6). C7 considers the generation of waste associated with the extraction, production, and transportation of materials. Similarly, C8 evaluates the same parameters during maintenance work. The energy involved in the production process of materials is assessed in C9. The total weight of the environmental impact was set at 25%, with C5, C6, C7, C8, and C9 weighted at 35%, 5%, 25%, 5%, and 30%, respectively.

The sub-division of C5 and C6 comprises parameters ranging from I9 to I13. All of these parameters consider the influence of each material used in construction. To estimate the values for I9 to I13, several studies were consulted [54,55,56]. It should be noted that the evaluation not only includes the deleterious effects of the materials on the environment but also the quantity of each material required for constructing the house. In these studies, the most relevant factor regarding the harmful effects of materials was CO₂ emissions, which were typically obtained through LCA. The relative consumption of each material concerning the total available amount was also estimated.

C7 and C8 consider the total amount of residue in parameter I14, which indicates the impact of the residue generated during the construction and maintenance of the house, respectively. To determine these proportions, references [52,53,55] were used. Lastly, in the environmental evaluation, C9 is assessed. This indicator is divided into parameters that consider the energy involved in the material throughout all its phases (I15), the processes carried out during construction (I16), and the energy consumed in the maintenance and service of the house (I17). Due to the long lifespan of houses, the energy consumed during the use of the house is considerably higher than that required for its construction. The balance between these two quantities depends on the characteristics and efficiency of the house, ranging from 2% to 38%. If the house is energy-efficient, this figure could be even higher. Consequently, I15 has been set to 25%, I17 to 70%, and I16 to 5%, corresponding to the energy consumed during the construction of the house. The values presented in the table correspond to those taken from [54].

The final part of the evaluation of the impact of the housing typology relates to the social effects, which have a weight of 25% in the total evaluation. This impact is divided into several aspects: design, construction, and maintenance, which are analysed in C10 (with 20% of the partial weight); the risks associated with the construction process and its use, which are evaluated in C11 (with 40% of the partial weight); and finally, the comfort experienced by the occupants of the house, which is considered in C12 (with the remaining 40% of the partial weight). As in the previous sections, parameters C10, C11, and C12 are composed of sub-categories that sum to another 100%. Given that the house is independent and this study considers the perspectives of the final user, C11 and C12 hold the greatest importance. These weights were inspired by [52,53,55,56].

During the design, construction, and maintenance of a house, several factors must be considered. Aspects related to worker comfort, such as noise, temperature, and distance from their homes, are included under parameter I18. This parameter holds a 40% weight in the partial evaluation of C10, reflecting the importance that recent regulations placed on working environments [57]. Environmental conditions, such as the amount of airborne particles and various forms of pollution, are covered by I19, which accounts for 15% of C10. A similar parameter during maintenance is also included under I19, contributing another 15%. Likewise, I20 addresses disturbances caused to traffic, nearby buildings, and the general environment during both construction and maintenance, with 15% attributed to the construction phase and the remaining 15% to the maintenance stage. Security and safety conditions are evaluated in C11, which is divided into three categories. Health and safety during construction, implied in I21, hold 85% of the weight of C11. I22 evaluates the subsidiary duties of the promoter during construction, contributing 10% to C11, while security against crime is considered in I23, with a 5% weight in C11. Finally, the comfort experienced by the inhabitants during the use of the house is considered in C12, which carries a 40% weight in the evaluation of the total social impact. C12 is further divided into thermal comfort (I24 with 25% of the weight), acoustic comfort (I25 with 25% of the weight), air quality and general comfort (I26 with 25% of the weight), and disturbances caused to neighbours by the presence of the house (I27 with the remaining 25%)

5. Sustainability Index and Value Function for Each Indicator

The sustainability index is obtained by weighting the values obtained from the value functions assigned to each indicator, multiplied by their respective weights and grouped into the criteria and the total requirement (See Figure 4). The value of a generic criterion (V_Cj) is provided by Equation (1). This is obtained by summing, from K = 1 to n (where n is the number of indicators in the criterion), the products of the value of each indicator (V_Ik), according to the associated weight (w_lk).

The same procedure is followed for the evaluation of the requirements. The value of a generic requirement (V_Ri) is obtained in Equation (2), which expresses the sum of j = 1 to l (where l is the number of criteria in the evaluated requirement) of the products of the value of each criterion (V_Cj) obtained in Equation (1), according to the associated weight (w_Cj).

$$V_{Cj}=\sum _{k=1}^n{w}_{lk}·V_{lk}$$

(1)

$$V_{Ri}=\sum _{j=1}^l{w}_{Cj}·V_{cj}$$

(2)

$$SI=\sum _{i=1}^j{w}_{Ri}·V_{Ri}$$

(3)

Finally, the sustainability index (SI) for each comparison is obtained by summing the dimensionless values of each requirement (V_Ri) multiplied by the corresponding weight for each of them (w_Ri), as shown in Equation (3). The subscript i represents the number of established requirements or demands, which is 3 (economic, social, and environmental) for sustainability studies [53].

For the definition of each function, the criteria outlined in various specific studies on the use of the MIVES methodology [49,59] were followed. It is worth emphasising the importance of defining the perspective of the evaluator (owner, building developer, etc.) [49]. The basic process for establishing the functions that assign value to the indicators listed in Table 1 can be summarised in the following points:

I.

Definition of the trend (increase or decrease) of the value function. The sign of the slope of the curve will depend on the nature of each indicator. An example of a decreasing function could be economic costs (Indicators I1–I2). Higher costs result in lower sustainability. On the contrary, an increasing indicator could be the durability of materials. Higher durability leads to a higher sustainability index. In Figure 5, decreasing functions are represented by dashed lines and increasing ones by solid lines.

II.

Definition of the points corresponding to the minimum (S_min, value 0) and maximum (S_max, value 10) satisfaction values. (S_min = minimum satisfaction, S_max = maximum satisfaction). The points of minimum and maximum satisfaction refer to values beyond which satisfaction no longer improves or deteriorates based on the evaluated variable and are reflected on the x-axis. In other words, they represent the boundaries within which the functions vary. The minimum satisfaction value indicates a score of 0, and the maximum satisfaction value is 10. As defined in some of the referenced studies [59], these points can be set based on various criteria: existing regulations and previous project experience.

III.

Definition of the shape of the value function (linear, concave, convex, S-shaped). The most common shapes of the functions established for evaluating the indicators are concave (a), convex (b), linear (c), or S-shaped (d) (see Figure 5). The choice of one type of function over another also depends on what was discussed in the first point and is closely tied to the nature of the indicator.

IV.

Definition of the mathematical expression for the value function. Finally, it is necessary to establish a mathematical function to obtain results based on the values of the variables studied. Equation (1) is the one proposed by studies of this method for evaluating each indicator [59]:

$$V_{ik}=B\ast \left[1-e^{{-K\ast \left({\displaystyle \frac{\left|X-S_{min}\right|}{C}}\right)}^P}\right],$$

(4)

where V_ik is the value of the evaluated indicator. B is a value that allows the equation to be established within the range of 0 to 10. This parameter represents the maximum satisfaction value, with B = 10. S_min is the point of minimum satisfaction associated with a value of 0. S_max is the point of maximum satisfaction associated with a value of 10. X is the abscissa that generates the value of V_ik. P is the parameter that shapes the curve. If P < 1, the curve is concave; if P > 1, the curve can be convex or S-shaped; for P = 1, it is linear. C is a parameter that approximately defines the value of X, where an inflection point occurs. K is a parameter that approximately defines the value of Y at point C, and lastly, B is represented by the value obtained in Equation (5):

$$B={\displaystyle \frac{1}{\left[1-e^{{-K\ast \left(\frac{\left|S_{max}-S_{min}\right|}{C}\right)}^P}\right]}}.$$

(5)

6. Results

6.1. Indicator Attainment

In order to establish all the data needed to perform the evaluation of the sustainability of the construction methods, research was conducted on the previous literature. In order to illustrate the complete process carried out for each indicator, the procedure for obtaining I14 is described next.

I14 represents the total residue and the utilization of materials during the construction phase. Various information from recent studies on waste management applied to single-family and non-single-family homes of around 100 m² was examined [60]. These studies provided insights into the average waste generation in conventional construction projects. Simultaneously, the construction systems of wood and industrialized construction or prefabricated systems were studied, and it was concluded that these construction methods produce less waste due to their higher quality control and process management in the factory, optimizing waste generation and facilitating reuse [52]. For this reason, the maximum value for this indicator was set based on the waste generated in conventional construction, with a value of 7.12 × 10⁻² m³/m² [60]. The minimum value was defined as zero waste generation, as any waste will have a negative impact on the environment. Similar studies have used a concave decreasing function for this type of analysis [52]. Therefore, the same criterion was followed for the evaluation in this study.

A similar process was carried out with all the indicators shown in previous studies, obtaining the values that appear in

Table 2. Basic data for each indicator.

Indicator	Units	Smax	Smin	C	K	P	Shape
I1	(EUR/m2)	400	1600	800	0.7	0.8	Concave
I2	(Months)	1	15	15	0.01	1	Linear
I4	(EUR/m2)	10	240	240	0.01	1	Linear
I5	(EUR/months∙m2)	0.75	3.55	3.55	0.01	1	Linear
I6	(EUR/m2)	0	1165	400	0.7	0.8	Concave
I7	(EUR/m2)	40	120	40	0.7	0.8	Concave
I8	(%)	100	0	100	0.01	1	Linear
I9	(Kg/m2)	0	2375	2375	0.01	1	Linear
I10	(Kg/m2)	0	125	125	0.01	1	Linear
I11	(Kg/m2)	0	150	150	0.01	1	Linear
I12	(Kg/m2)	0	400	400	0.01	1	Linear
I14	(m3/m2)	0	7.12 × 10−2	4.00 × 10−2	0.7	0.8	Concave
I15	(MJ/m2)	0	5760	1500	1	1	Concave
I17	(MJ/m2∙K)	400	0	200	0.7	0.8	Concave
I18	(%)	100	0	100	0.01	1	Linear
I19	(% × factor)	100	0	100	0.01	1	Linear
I20	(% × factor)	0	100	100	0.01	1	Linear
I21	(Points)	0	100	100	0.01	2	Convex
I22	(%)	100	0	100	0.01	2	Convex
I24	(°C)	0	8	8	0.01	1	Linear
I25	(dBA)	10	40	20	1	1	Concave

. It should be noted that the indicators I3, I13, I16, I23, and I26-27 are not present in table, as they account for qualitative parameters.

6.2. Economic Evaluation

From an economic perspective, it has been observed that the initial costs of the project (Direct Costs, I1) continue to make the traditional system highly competitive and provide a significant advantage to prefabricated wooden systems. However, these costs can vary significantly and depend on the timing and location of the housing construction. The costs stipulated for this indicator were based on projects with similar characteristics recently carried out in the Madrid region, for which data were obtained, as shown in Table 2. When considering the indirect costs associated with the time (I2) and financial and insurance costs (I3), the MDR system begins to gain importance. It should be considered that the insurance costs will be lower for higher-quality construction, which is the case for the MDR system compared to both the traditional and timber systems. Thus, the value of I3 differs in each case. However, the MDR system still remains the less favourable option according to C1.

However, it is true that, similar to what happens in civil engineering projects, the money invested in the project phase is typically saved exponentially during the construction and maintenance stages. A similar conclusion can be drawn for MDR systems. These systems involve a highly controlled industrial process with infrastructure costs, skilled and trained workers, an efficient network of suppliers, and numerous advantages inherent to industrialized processes. This means that while the initial costs may be higher, these costs decrease over the long term across other criteria, such as the non-conformity quality costs (C2) and the life span-associated costs (C3), due to the system’s efficiency and product quality. Supporting this argument are data showing that non-conformity expenses (I4) account for only 3% of the total cost in MDR systems, compared to 6% in industrialized timber construction and 10% in the traditional method.

Throughout its lifespan, as analysed in I5, both the maintenance costs and energy consumption costs were considered. Maintenance of the general aspects of the house may be similar between industrialised timber systems and the traditional system. Nonetheless, wood requires additional maintenance such as varnishing, sanding, painting, etc., which is conducted more frequently than in the traditional system [61,62]. In contrast, the MDR system uses more durable materials, primarily reinforced concrete. It does not have suspended ceilings or plaster, which deteriorate over time. In the case of paints, it is widely known that they are more long-lasting in the MDR system, as they adhere directly to the concrete, resulting in better durability. All of this implies less maintenance over its lifespan. In addition, an advantage has also been given to the MDR system, as the industrialised system will always meet the structural and quality requirements imposed by regulations, enduring over time and retaining its value.

From an energy cost perspective, the average costs associated with traditional constructions in Spain have been compared with those of more efficient construction methods, such as wood or the MDR system. Savings of around 40% were estimated in the industrialised methods compared to the traditional one [63]. This is a conservative estimate, considering that some studies suggest a 60% reduction.

Moreover, there are costs associated with the risks that the house may be exposed to throughout its lifespan (I6). These costs have been estimated based on the concept of structural robustness [64], where the MDR system, due to its monolithic structure, has been rated the highest, without undervaluing the traditional and wooden systems that comply with the CTE requirements [65].

A structure is considered robust when the failure of a component does not result in catastrophic consequences. To analyse each system, a robustness percentage was established ranging from 0 to 100, where 100 represents total safety and 0 complete failure. Significant failures, such as issues with the foundation or structural collapse, can be triggered by factors like fires, earthquakes, floods, and strong winds. Therefore, given the characteristics of each construction system, it has been verified that the one offering the best safety guarantees is the MDR system. This conclusion is based on two factors: first, its monolithic composition provides extensive structural integrity; second, it is not anchored to the foundation, reducing the risk of cracks or structural collapse during events such as earthquakes or strong winds. Consequently, this system was weighted at 80% for maximum structural robustness. On the contrary, the CTE [65] requires structures to have specific characteristics to ensure compliance with these types of events that are less often obtained using the traditional system. Therefore, it was weighted at 60% for structural robustness. Lastly, wood, although it meets the minimum requirements set by the building code [65], will always be more vulnerable to fires due to its inherent combustibility, as well as extreme wind forces, given its lower weight and stability against such harsh conditions. Consequently, the structural robustness for wood was estimated at 30%. These percentages represent the estimated cost of recovery in case of any of these events. Additionally, the time during which the property would remain unusable due to the effects of the event was considered, based on the same time criterion used in I2.

Finally, the end-of-life evaluation of the infrastructure during its dismantling or demolition (C4) was assessed. For this, the average costs of specialised companies were evaluated, along with the possibility of reusing materials to gain an economic return.

6.3. Environmental Evaluation

When evaluating the environmental impact of construction methods and analysing the values obtained in

Table 3. Result of MIVES.

			TRADITIONAL				TIMBER				MDR
Requirements	Criteria	Indicators	Mark × Weight E.	Mark × Weight C.	Mark × Weight I.	Mark (0–10)	Mark × Weight E.	Mark × Weight C.	Mark × Weight I.	Mark (0–10)	Mark × Weight E.	Mark × Weight C.	Mark × Weight I.	Mark (0–10)
E1. Economic	C1	I1	3.06	3.57	6.40	7.5	3.30	3.82	7.13	8.4	3.61	3.56	5.85	6.9
		I2			0.11	2.2			0.39	7.9			0.39	7.9
		I3			0.63	6.3			0.13	1.3			0.88	8.8
	C2	I4		0.65	6.53	6.5		0.85	8.48	8.5		0.91	9.13	9.1
	C3	I5		1.53	3.44	4.3		1.34	3.30	4.2		2.40	6.15	7.7
		I6			1.65	8.2			1.16	5.8			1.85	9.3
	C4	I7		0.38	3.81	7.6		0.60	5.00	10.0		0.35	0.00	0.0
		I8			0.00	0.0			1.01	2.0			3.51	7.0
E2. Environmental	C5	I9	0.90	1.07	1.80	5.1	1.83	2.42	3.32	9.5	1.61	1.44	0.00	0.0
		I10			0.02	0.2			0.85	8.5			0.56	5.6
		I11			0.49	9.7			0.00	0.0			0.50	9.9
		I12			0.00	0.0			2.00	10.0			1.55	7.8
		I13			0.75	2.5			0.75	2.5			1.50	5.0
	C6	I9		0.20	2.82	8.1		0.35	3.43	9.8		0.25	2.95	8.4
		I10			0.02	0.2			0.85	8.5			0.21	2.1
		I11			0.49	9.7			0.00	0.0			0.49	9.8
		I12			0.00	0.0			2.00	10.0			0.40	2.0
		I13			0.75	2.5			0.75	2.5			0.90	3.0
	C7	I14		0.16	0.62	0.6		1.78	7.10	7.1		2.26	9.04	9.0
	C8	I14		0.03	0.62	0.6		0.26	5.13	5.1		0.22	4.30	4.3
	C9	I15		2.15	0.88	3.5		2.50	1.56	6.2		2.27	0.62	2.5
		I16			0.13	2.5			0.38	7.5			0.25	5.0
		I17			6.17	8.8			6.40	9.1			6.70	9.6
E3. Social	C10	I18	0.61	0.00	0.00	0.0	1.58	1.04	2.00	5.0	1.95	1.21	3.20	8.0
		I19			0.00	0.0			1.13	7.5			1.20	8.0
		I20			0.00	0.0			0.75	5.0			1.05	7.0
		I19			0.00	0.0			0.75	5.0			0.30	2.0
		I20			0.00	0.0			0.56	3.8			0.30	2.0
	C11	I21		0.73	1.45	1.7		2.66	6.33	7.5		3.00	6.52	7.7
		I22			0.00	0.0			0.19	1.9			0.49	4.9
		I23			0.38	7.5			0.13	2.5			0.50	10.0
	C12	I24		1.72	1.33	5.3		2.62	1.63	6.5		3.59	2.03	8.1
		I25			1.27	5.1			2.04	8.1			2.20	8.8
		I26			0.63	2.5			1.25	5.0			2.50	10.0
		I27			1.08	4.3			1.64	6.6			2.25	9.0
SUSTAINABILITY INDEX (SI)			4.58				6.71				7.17

, it can be concluded that wood is the most effective material for construction, as previously mentioned in the literature [66]. This result supports the MIVES methodology used in this study. The analysis is based on the condition that the wood originates from sustainably managed forests and plantations, certified by the Forest Stewardship Council (FSC) [67]. This certification is endorsed by wood-producing and trading companies, environmental organizations, and human rights groups concerned with global deforestation. The certification ensures that the wood is sourced from responsibly managed forests. Therefore, in assessing wood consumption, only its contribution to potential global warming is considered, without evaluating the other associated impacts.

C5 evaluates the impact of material use during the construction phase in terms of the potential contribution to global warming, measured in kg/m². Generally, the use of concrete (I9) significantly disadvantages both the traditional method and the MDR system due to the high CO₂ emissions associated with cement production [9]. The quantities of materials used in both systems were obtained from the manufacturer of MDR modules and cross-referenced with similar projects. For the prefabricated wooden system, data from studies [49,50] were used. It should be noted that the amount of concrete used in the MDR system is double that used in the traditional system: 2375 kg/m² compared to 1160 kg/m², respectively. However, the MDR system is significantly favoured when the volume of concrete used includes the foundations, as it requires only half the slab thickness compared to the traditional system. This advantage is due to the even distribution of loads that the MDR system transfers to the ground, owing to the structural configuration of the modules. Regarding the foundations for the wooden systems, a smaller volume is required due to the lighter weight of the system.

External and internal walls are commonly formed by ceramic elements bonded with cement mortar in the traditional construction method. In addition, the roof is commonly composed of layers of ceramic tiles both in the traditional and MDR system. The impact of the use of both ceramic tiles and bricks and cement mortar is evaluated in indicators I10 and I12. In this case, the traditional construction method is remarkably detrimental to the environment because both materials possess a high potential impact for global warming due to the energy spent in the production processes of cement and ceramic elements such as bricks or tiles. On the contrary, the use of such materials in the MDR system and the wooden prefabricated system is remarkably lower than in the traditional system. In contrast, the use of wood is notably limited in the case of the traditional system and the MDR, while it is ubiquitous in the case of the wooden prefabricated one. That difference accounts for the remarkable variation in I11 in

Table 4. Economic evaluation. Dimensionless values after weighting (Variables and weights taken from Table 1).

	Global	C1	C2	C3	C4
Traditional	3.06	3.57	0.65	1.53	0.38
Wood	3.30	3.82	0.85	1.34	0.60
MDR	3.61	3.56	0.91	2.40	0.35

. The use of other materials (I13) credits the impact of materials such as plaster, paints, resins, etc. Since it was not possible to adequately quantify the use of these other materials, a qualitative assessment was carried out for this category among the different techniques used. I13 contains only those materials whose use is linked to the type of construction. On the contrary, those linked to plumbing, isolation, wooden carpentry, etc., were ignored. Based on these criteria, a weighting was established on a scale of ten points, with 2.5 for the traditional system, 2.5 for the wooden system, and 5.0 for the MDR system. This can be justified based on several considerations. In the case of wood, it is necessary to use a wide range of auxiliary materials such as varnishes, fire protection paints, larger amounts of insulation due to the low thickness of the wood layers, plaster in damp areas, etc. In the case of the traditional system, the use of materials for suspended ceilings, plaster, and coatings on numerous elements is also necessary to achieve relatively high-quality finishes. However, in the MDR system, with perfect concrete finishes, only paint is needed as an auxiliary material for finishing. Additionally, it uses some other materials such as high-resistance resins for module joining or structural metallic elements like lifting hooks for handling. The use of auxiliary materials is similar in the cases of the traditional system of construction and the timber one, and consequently the value of the parameter is the same. On the contrary, the MDR system uses a much smaller amount of materials; therefore, I13 is 100% more beneficial.

Criterion C6 evaluated the use of the same materials analysed in C5 in the maintenance phases. It should be borne in mind that the quantities used in this phase are lower than those in construction. The greater durability of the MDR system compared to the other two systems was assessed, and the same considerations used in C5 were applied. Therefore, the same score was assigned to each system, taking into account that the prefabricated wooden system proportionally uses the same quantities as in the construction phase, unlike the amount of concrete, which is estimated to be reduced by 60% in proportion to the construction phase. Regarding the traditional system, as in the case of the wooden one, a 60% reduction in material use is estimated relative to the construction phase. In the case of the MDR system, it adopts the values (proportional to the maintenance phase) used by the traditional system in the construction phase. However, the durability and quality factor inherent in the MDR system, as an industrialised system, was implicitly considered. Due to its control processes and product quality, maintenance in this system is less necessary and can be performed less frequently compared to other systems. For this reason, the proportional values of the traditional system were reduced by 20% in order to take into account the particularities of the MDR system.

The criteria C7 and C8 address the generation of waste in both the construction and maintenance stages. The values for waste generation were derived from the average of numerous constructions carried out using the traditional system [60]. The main parameter considered both in C7 and C8 is the degree of industrialization. It has been assumed that a higher degree of industrialization implies greater control of processes and optimization of materials, resulting in a lower generation of waste. Based on this reasoning, the degrees of industrialization of the traditional system were estimated at 0%, the wood prefabricated system at 50%, and the MDR system at 80%. This implies that wood and the MDR system generate 50% and 80% less waste, respectively, compared to the traditional system. A similar assumption was made dealing with the maintenance labour required; consequently, the same percentages were chosen. However, the complexity of the labour involved in the maintenance stage is considered 20% less intensive than in the construction stage. The hypotheses assumed are similar to the previously published data [52].

The final parameter contributing to the economic evaluations is C9. This parameter was segmented into three indicators: I15, which estimates the energy consumption involved in the manufacture of materials; I16, which assesses the energy required during the construction stage; and I17, which summarizes the energy needs over the lifespan of the house. For I15, calculations of the embodied energy were carried out based on the quantity of each material used, along with their energy contributions, obtained from specific studies on the life cycle assessment (LCA) of materials [54]. The results revealed that the MDR system is penalized due to its greater use of concrete, followed by the traditional system. In contrast, the wooden system achieved the highest score with the lowest energy consumption. I16 considers the straightforward assembly process of the prefabricated wooden system, which requires no special transport, basic tools, and has a short construction duration. Conversely, traditional systems require much longer construction times, negatively impacting their assessment. The MDR system, although involving a brief assembly phase, requires the use of large machinery for installation. Consequently, it was evaluated more favourably than the traditional system, as the impact is confined to a single day compared to a year. Additionally, the energy consumption during construction is related to the weights that need to be lifted and the machinery required. Taking this into account, the system with the lowest weight, the timber system, should receive the highest score. The traditional system, which requires a high number of lifting procedures, has the lowest I16 value. The MDR system sits between the two, as it requires lifting heavy loads but only a limited number of times. Lastly, the results for the energy consumption throughout the lifespan (I17) were derived from the heat transmission and insulation capacity of each material [68].

6.4. Social Evaluation

The final aspect covered in the MIVES evaluation is the assessment of the social impact of the construction methods, which is composed of C10, C11, and C12. C10 is determined by analysing the indicators I18, I19, and I20. I18 summarizes the comfort of the workers during the construction of the house, considering factors such as the thermal comfort, the protection against inclement weather, the distance to the work site, and other relevant aspects, with industrialized methodologies receiving the highest benefit. I19 accounts for the air and noise pollution during construction, while I20 assesses the potential disturbances experienced by third parties due to the construction process. For these last two indicators, there is a clear correlation with the level of automation in the processes, with more automated processes receiving more favourable evaluations. Consequently, the traditional system, the wooden prefabricated system, and the MDR system are rated at 0, 1.04, and 1.21, respectively. C11 considers the impact on the health and safety conditions during the construction and maintenance, as well as the overall safety of the construction. For risk assessment, criteria from similar studies [45] and statistics on workplace accidents in Spain [69] were analysed, concluding that both wood and industrialized systems offer greater safety compared to the traditional system. The promoter’s liability risk for workplace accidents is closely linked to the degree of process control and time spent on the construction site (industrialization), as well as the risks associated with site operations. This justifies the higher value of I22 for the wooden industrialized system, with an even better score for the MDR system. In terms of safety, I23 indicates that the most robust construction will provide better protection. Therefore, the monolithic MDR system boasts the highest value, compared to the traditional system, which is in the middle, and the timber construction techniques, which score the lowest.

In criterion C12, an evaluation is made regarding the internal comfort of the occupants and their neighbours, once the housing is occupied. Various aspects were assessed, including the thermal comfort (I24), acoustic comfort (I25), functional comfort, and others (I26), as well as the neighbourhood’s comfort concerning the housing activity (I27). For indicator I25, a report establishes a temperature difference between the exterior and interior of 15 °C, following thermal insulation tests, when the exterior temperature was around 40°C. Due to the lack of precise data for the traditional system and the prefabricated wooden system, a linear relationship was established with the concept of thermal inertia used in I17. A similar situation arises in evaluating the acoustic insulation; therefore, a qualitative method was employed for this indicator, based on the following assumptions. The exterior insulation is assumed to be dimensioned according to the minimum requirements set by the CTE [65], ensuring compliance across all systems. However, the insulation between interior compartments is closely related to the material composition. Based on the characteristics of the interior partitions in the construction types and the data provided by the MDR system, the following conclusions were drawn. The MDR system had a rating 20% below the minimum values established by the norm, i.e., a maximum of 17 dBA. The traditional system was rated between the maximum and minimum values, as it must comply with CTE specifications, i.e., 30 dBA. For the wooden system, acoustic insulation was considered higher than the traditional system, because wood is a highly sound-absorbent material. However, due to the thinner partitions used, it was not considered to surpass the acoustic capacity of the MDR system, with a value set at 20 dBA. Indicator I26 was evaluated based on qualitative factors such as the quality of finishes, the appearance of cracks or dampness, and the resilience of finishes against incidental impacts. Scores of 2.5, 5.0, and 7.5 were assigned to the traditional, wooden, and MDR systems, respectively. Finally, indicator I27 establishes a relationship between indicators I24, I25, and I26 with respect to their impact on others. Thus, this indicator was evaluated as a weighted average of the other three indicators for the final score. While the parameters related to I26 and I27 may be somewhat subjective, it is important to note that better finishes and higher quality construction processes are key to achieving greater comfort. This justifies the differences in the I26 and I27 values.

7. Discussion

Table 1 presents all the values obtained in the previous section. However, to facilitate the comparison between construction systems, these values were divided into economic, environmental, and social costs. Below, Table 4 provides a summary of the economic criteria directly derived from the values observed in Table 3.

From Table 4, it can be observed that the MDR system is 9% and 18% more cost-effective than the wood and traditional systems, respectively. Additionally, wood is 8% more cost-effective than the traditional system. It is important to note that, while the MDR system has higher direct costs, it incurs lower indirect costs, making it comparable to the traditional system in terms of overall cost-effectiveness (C1). Wood has the advantage in this category, being the most favourable option. However, when considering the quality and costs over the lifespan (as in C2 and C3), the MDR system significantly outperforms the other two, establishing a clear advantage and positioning itself as the optimal system among the three considered.

From Table 4 it is easy to perceive that wood excels in total costs (C1; direct + indirect), also positioning itself with low non-quality costs (C2) and gaining a clear advantage in dismantling costs (C4), where it is clearly the most advantageous system. Nonetheless, this system is clearly affected by the high maintenance costs inherent to wood.

Table 5. Environmental evaluation. Dimensionless values after weighting (Variables and weights taken from Table 1.).

	Global	C5	C6	C7	C8	C9
Traditional	0.90	1.07	0.20	0.16	0.03	2.15
Wood	1.83	2.42	0.35	1.78	0.26	2.50
MDR	1.61	1.44	0.25	2.26	0.22	2.27

provides a summary of the environmental evaluation. It shows that the most environmentally friendly method is the prefabricated wooden system, which is 13% and 101% more efficient than the MDR and traditional systems, respectively. The significant differences between the prefabricated systems and the traditional one highlight the inefficiencies of the traditional system in material use, construction processes, waste management, and energy consumption. Additionally, it is important to note that industrialized methods show a considerable improvement in terms of the environmental impact, even when using the same materials. This is evident when comparing the overall environmental evaluation of the traditional system with that of the MDR system.

A summary of the social evaluation can be seen in

Table 6. Social evaluation. Dimensionless values after weighting (Variables and weights taken from Table 1).

	Global	C10	C11	C12
Traditional	0.61	0.00	0.73	1.72
Wood	1.58	1.04	2.66	2.62
MDR	1.95	1.21	3.00	3.59

. Analysing the data from Table 6, the following conclusions can be drawn. Overall, the most efficient system in the social spectrum is clearly the MDR system. It is 24% and 219% more efficient than the wood and traditional systems, respectively. The wood system is 158% more efficient than the traditional system. This construction technique is greatly disadvantaged in terms of the work comfort and the externalities it causes when all stages of the construction occur in the construction site. Additionally, its positioning regarding risks, safety, and health is very low. In terms of internal comfort, it achieves a higher score since the technical code regulations place significant emphasis on these aspects of habitability [65].

Between the wood system and the MDR system, a significant advantage of the latter is observed in all criteria. This is closely linked to the degree of industrialization and the development of a highly efficient construction process that ensures the safety and comfort of all involved agents, risk prevention, and the highest quality for the end user.

8. Conclusions

This study shows the assessment of the implications of the housing typology on sustainability. To achieve this, a multicriteria decision-making method based on MIVES was used. MIVES has proven that it is capable of integrating economic, social, and environmental parameters, and it can differentiate with precision most of the relevant aspects that distinguish the overall sustainability of the analysed construction systems.

From the economic point of view, the analysis carried out determined that the MDR system is the most favourable of all the systems studied. On the contrary, only slight differences were detected, as the result of the MDR system was only 17.97% greater than the traditional system and 9.39% higher than the timber system.

Regarding the environmental evaluation, MIVES was capable of detecting that the construction system with timber was the best one among the three systems studied. The timber construction method was 13.66% better than the MDR system and 103.33% better than the traditional construction techniques.

According to MIVES, the social impact of the MDR system was more reduced than the timber construction method and the traditional one. It should be underlined that the traditional system achieved poor results at only 31.12% of the mark obtained by the MDR. In addition, the construction with timber obtained only 81.02% of the evaluation obtained by the MDR. This construction technique is greatly disadvantaged in terms of the work comfort and the externalities it causes when all stages of the construction occur at the construction site.

The present study might be expanded in the near future by analysing other types of construction methods such as 3D printing and steel-structure typologies. In addition, the authors acknowledge that some aspects of the analysis might not reflect the reality of the construction methods in other parts of the globe, as they typical of advanced countries.