In the Solar Decathlon Competition: a Proposed Housing Model Based on a Prefabricated Structural System

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Article “Methodology Comparative Analysis” in the Solar Decathlon Competition: A Proposed Housing Model based on a Prefabricated Structural System

J.F. Luna-Tintos 1 , Carlos Cobreros 2 , Rafael Herrera-Limones 3,* and Álvaro López-Escamilla 3 1 Facultad de Ingeniería, Universidad Autónoma de Querétaro, Santiago de Querétaro 76010, Mexico; [email protected] 2 Tecnológico de Monterrey, Escuela de Arquitectura, Arte y Diseño, Santiago de Querétaro 76140, Mexico; [email protected] 3 Instituto Universitario de Arquitectura y Ciencias de la Construcción, Escuela Técnica Superior de Arquitectura, Universidad de Sevilla, 41012 Seville, Spain; [email protected] * Correspondence: [email protected]; Tel.: +34-954-55-65-20

Received: 18 January 2020; Accepted: 28 February 2020; Published: 2 March 2020

Abstract: The construction sector, by direct or indirect actions, consumes more than 40% of the global energy produced and is responsible for 30% of CO2 emissions. It is a need of the construction industry to transform its practices and processes by proposing systems of lower demand to the environment. In this sense, closed prefabrication and industrialization as a constructive process could be the key to seek savings and eﬃciency from its origin to the end of life of buildings. In this context, this article presents a methodological proposal of quantitative, qualitative and comparative analysis of the structural systems of eight prototypes presented in the “Solar Decathlon” contest in its North-American and Latin-American editions (both of them in 2015) and the European edition (in 2014). This methodology deduces the characteristics of a structural system of lower environmental demand and the characteristics of these constructive processes, in favor of a new paradigm of sustainability and to be applied in innovative systems of new housing models.

Keywords: solar; prototype; system structure; construction; prefabrication; industrialization; sustainability; environmental; architecture; competition

1. Introduction The construction industry is responsible, through the construction and the conditions that predispose for the operation of the buildings, for around 40% of the global energy use [1,2], 25% of the world water consumption and 30% of the emissions of greenhouse gases [3]. In this sense, it is essential to motivate interest and increase the consideration of designers, architects, builders and other actors involved in the industry, to reduce the environmental impact for which this activity is responsible [4,5]. On the one hand, based on the fact that the construction is still based on artisanal work with little precision, no repetitiveness in operations, no systematic control of finished quality, rationalization and guarantee of supplies; and on the other, that there is a great dispersion and waste of materials and construction systems that coexist in the market and are part of the building works [6], it is consequent that actions that allow to close the material cycles as a condition of sustainability and good practices to cushion the impact of this activity are made difficult [7]. In this sense, prefabrication and industrialization, as a constructive process, could be the key to seek savings and efficiency from origin and conception based on design and manufacturing, namely the efficiency and savings due to the speed of the construction, the saving and efficiency in the useful

Sustainability 2020, 12, 1882; doi:10.3390/su12051882 www.mdpi.com/journal/sustainability Sustainability 2020, 12, 1882 2 of 17 life of the building by the incorporated technique and, inclusively, saving and efficiency in the end of life of the building [8]. However, prefabricated and industrialized systems often face the inertias related to traditional ways of building and the technical ignorance that this constructive process entails [9]. Likewise, some other problems faced by architects in general when designing and constructively defining prefabricated or industrialized solutions are the absence of reference manuals, the lack of knowledge of design limitations and the restrictions of the industry and the methods or materials; the consequences of this ignorance are errors of definition in the project and construction that in turn generate increase in terms and costs or even abandonment of the type of construction systems chosen [10–12]. Therefore, to reinforce the use of this type of constructive processes, it is fundamental, firstly, to understand the industrial context and the need to modify constructive habits. Also, it is important to highlight and promote the environmental benefits of these practices and take into account the satisfaction and possibility of participation in the process of the end user. In this sense, it is well known that, in the search for architectural models and sustainable constructive innovations, competitions are a meeting point in which knowledge applied to society’s sustainability is generated and disseminated [13]. Based on this, the Solar Decathlon (SD) was chosen as the case study competition for the development of this research. The Solar Decathlon it is the most important sustainable habitat competition for university students in the world. It is a research project of a competitive, international and institutional nature which constitutes a commitment to the future for sustainability, encompassing architecture and technologies for solar use and home automation, where the design and development of a self-sustaining and energetically autonomous dwelling is competed, using as much energy as possible and in the most efficient way [14,15]. In this competition, colleges and universities from all over the world participate, in collaboration with institutions and private companies, with the objective of designing and building a full-scale housing prototype with the maximum level of self-sufficiency, energetically autonomous, with an optimal cost and operation [16,17]. With a fundamental difference from other competitions, the projects are constructed, their consumption is measured and, finally, they are evaluated in a competitive way compared to other solutions, in theory, equally valid [18]. During the 15-day competition period in the “solar city” site, the prototypes (1:1 scale) are exhibited and evaluated in ten contests (hence the name decathlon). These are: Architecture, Energy Efficiency, Engineering and Construction, Comfort, Marketing and Communication, Electrical Energy Balance, House Functioning, Innovation, Urban Design and Affordability and Sustainability [19]. It is important to note that in the “Engineering and Construction” contest, the objective is to evaluate the design and implementation of the construction and engineering system at the competition site. The teams must therefore demonstrate the prototype’s viability, adequate integration and maximum structural functionality alongside the adequate design of the electrical and solar energy production systems [20]. This contest has now expanded internationally, with six editions of the competition worldwide (Table1)[ 21], where each one makes public the technical information of the contest projects, which is a source of immense value since these prototypes represent the biggest innovations in the design and construction industry. Different projects of different editions of the contest have been the object of study of several research articles, books and theses of undergraduate and postgraduate studies [22]. Sustainability 2020, 12, 1882 3 of 17

Table 1. Timeline of editions of the Solar Decathlon competition.

Solar Decathlon Country Year Washington D.C. 2002 Washington D.C. 2005 Washington D.C. 2007 Washington D.C. 2009 US Washington D.C. 2011 Irvine, California 2013 Irvine, California 2015—Case Study • Denver, Colorado 2017 Africa Ben Guerir, Morocco 2019 Datong 2013 China Dezhou 2018 Madrid, Spain 2010 Madrid, Spain 2012 Europe Paris–Versailles, France 2014—Case Study • Szentendre–Budapest, Hungary 2019 Wuppertal, Germany 2021—Edition In Progress Santiago de Cali, Colombia 2015—Case Study Latin America and Caribbean • Santiago de Cali, Colombia 2019—Edition In Progress Dubai, United Arab Emirates 2018 Middle East Dubai, United Arab Emirates 2020—Edition In Progress The is used to indicate that the edition has been chosen as a case study. •

In this regard, it is worth noting the large amount of detailed information presented by each team, with a considerable number of plans and reports from different authors, so it is very important to review and take as reference different methodologies used to analyze and compare this documentation [23–25], where files are proposed and used that through graphics analyze the SD prototypes and their constructive details. Derived from what is mentioned above, it is considered that the suitability of this article lies in the need to lay the foundations for a change in the more widespread and conventional construction models in Latin–Mediterranean countries, where the use of construction systems based on industrialization and prefabricated architecture are still underdeveloped and are sometimes contaminated by the weaknesses of traditional construction. Thus, the main objective of this article will be to develop an evaluation methodology for construction systems focused on industrialization, through which we can objectify the overall quality of these systems. While it can be understood that many construction systems can have the prefabricated label, not all meet the highest expectations, if we focus on sustainability and efficient resource management. Based on this, the second objective will be to put into crisis the evaluation methodology used by the prestigious Solar Decathlon contest, the source of our case studies, to score the “Engineering and Construction” test. As this is a subjective methodology, the materiality of the system, its weight or resources to be used in its assembly or its adaptability are not quantitatively differentiated. Therefore, in this article, an original objective evaluation methodology will be developed and exposed, applying it to the prototypes with the highest score in the “Engineering and Construction” test Sustainability 2020, 12, 1882 4 of 17 of several editions of the competition. This methodology could be used as an evaluation tool for future labels or protocols, intended to “reward” construction systems with low impact on the environment. To achieve this objective, the proposed methodology is described below.

2. Methodology In order to achieve the proposed objectives, it is ﬁrst necessary to deﬁne the prototype case study of the editions of Solar Decathlon competition held until now (Table1) that, for purposes related to the development of this research, in the proposed methodology, are considered. The three structural solutions of the prototypes best rated by the jury in the “Engineering/Engineering and Construction” contest of the editions Solar Decathlon North America 2015 (SDEE.UU.2015) and Solar Decathlon Europe 2014 (SDEU 2014) are considered. Likewise, the 2015 edition of the Latin America and Caribbean Solar Decathlon (SDLAC2015) considered two prototypes that, due to their structural system as a solution to the problems of their location, contribute great value to the development of this research. For example, there is the Kuxtal (Mexico) proposal that aims to satisfy the needs of progressivity, perfectibility, heritage and self-construction in Mexico, or the Aura Project (Spain), which is based on a study of the Latin–Mediterranean tradition and the reformulation of all its concepts, through a fragmented and shared residential substrate that uses as a repetitive tridimensional module of self-construction that accumulates all the minimum housing requirements [26]. Consequently, the editions of the Solar Decathlon competition held in North America, Europe and Latin America between 2014 and 2015 are used as case studies for this research. This permits a global vision of the direction being taken in research focused on construction in western culture. Furthermore, taking into consideration that all these editions are linked in the context of time and space and the research is carried out by members of the Kuxtal (Mexico) and Aura (Spain) teams participating in the Solar Decathlon Latin America and Caribbean 2015 (SDLAC15), there is an alignment with the Latin–Mediterranean link in which construction is contemplated from a similar cultural perspective. Having said this, there are two stages of analysis in the methodology (Figure1):

Firstly, there is the descriptive–qualitative–comparative analysis, where each of the case study • prototypes (Table2) is described and studied based on a series of criteria /parameters that analyze their constructive and structural characteristics. In this part, it is necessary to review the aspects that were weighted in the tests of each of the SD versions mentioned above, to subsequently recover those that assessed the characteristics of the structural system and its relationship to the living spaces that emerge from it, in order to later include other parameters of own contribution that are considered fundamental for the intended analysis. This being said, the parameters with which the comparative analysis is performed are: concept, typology, materiality, weight, area, possibility of assembly/disassembly, modularizable nature, prefabrication, industrialization, efficacy in placing, savings and quickness in construction, LCA consideration, flexibility, adaptability, perfectibility, accessibility and availability of materials, use of indigenous material, waste management during construction, recycling possibility of elements and reuse possibility of elements. Secondly, a quantitative–comparative evaluation is proposed (valued from 1 to 4, with 1 being • the lowest rating and 4 the highest weighting) of the principal parameters and qualities of the prefabricated and industrialized structural systems with respect to the conventional structural systems, recovered from the qualitative analysis; this is in order to obtain a qualification that would allow a comparison between prototypes, an easy understanding of the main parameters and the results of the quantitative analysis of these in the prototypes in the competition. Sustainability 2020, 12, 1882 5 of 17

Figure 1. Methodology followed for research development.

Table 2. Case Study.

Test score of “Engineering Solar Decathlon Team and Construction” SU + RE House—Stevens Institute of 93/100 Technology Casa del Sol—University of California, U.S. 2015 Irvine, Chapman University and Irvine 92/100 Valley College Nexushaus—University of Texas at Austin 91/100 and Technical University of Munich CASA—National Autonomous University of Mexico and the Research Center in Industrial Design and the School of 80/80 Engineering and the School of Arts (Mexico) Europe 2014 Renaihouse—University of Chiba (Japan). 76/80 Casa Fénix— Technical University Federico Santa María - Valparaíso (Chile) 72/80 and University Rochelle - Espace Bois de l’IUT (France). Aura Project—University of Sevilla and University Santiago de Cali 85/100 Latin America and (Spain–Colombia). Caribbean 2015 Kuxtal— Monterrey Institute of Technology and Higher Education, 80/100 Querétero Campus (Mexico)

In the presented table below, the teams of the case study prototypes, the edition of the contest in which they competed and the score obtained are compiled. Next, these parameters are listed and the proposed rubric is exposed to determine the weightings of the prototypes.

Sustainability 2020, 12, 1882 6 of 17

A. Materiality This refers to the materials that were used in the structural system. For the weighting of this parameter, the “Red List” developed by the International Living Future Institute is considered. This list is composed of materials that should be gradually withdrawn from production due to health problems, with the intention of eliminating the worst materials and practices, encouraging manufacturers and distributors to commercialize truly responsible materials for the environment and the people who inhabit it [27] (Table3).

Table 3. Materiality assessment rubric.

A. Materiality 1 2 3 4 If three or more of the If two of the materials If one of the materials If none of the materials materials used in the used in the structural used in the structural used in the structural structural resolution resolution (primary resolution (primary resolution (primary (primary structure, structure, secondary structure, secondary structure, secondary secondary structure and structure and auxiliary structure and auxiliary structure and auxiliary auxiliary structure of structure of wall, floor structure of wall, floor structure of wall, floor wall, floor and ceiling and ceiling support) and ceiling support) and ceiling support) support) belong to the belong to the LBC Red belong to the LBC Red belong to the LBC Red LBC Red List. List. List. List.

B. Possibility of assembly/disassembly and efficiency in the placement (savings and quickness in the construction). This evaluates the possibility of the structure to be assembled and disassembled, through the union of its different elements, giving to them the quality of being reused in the same structure or in another, even with different location, as a result of the correct choice of the connections between the elements that compose the substructures and the structural system. Likewise, the time required and the strategy of placing and building components (Table4) are considered.

Table 4. Possibility of assembly/disassembly and eﬃciency in the placement (savings and quickness in the construction) assessment rubric.

B. Possibility of assembly/disassembly and efficiency in the placement (savings and quickness in the construction) 1 2 3 4 If none of the If some of the If all the elements used in elements used in the elements used in the If all the elements the structural resolution structural resolution structural resolution used in the structural (primary structure, (primary structure, (primary structure, resolution (primary secondary structure and secondary structure secondary structure structure, secondary auxiliary structure of wall, and auxiliary and auxiliary structure and floor and ceiling support) structure of wall, structure of wall, auxiliary structure of can be assembled and floor and ceiling floor and ceiling wall, floor and ceiling disassembled, allowing their support) can be support) can be support) can be reuse in the same structure assembled and assembled and assembled and or in another, and if the disassembled, disassembled, disassembled, strategy of placing and making it impossible allowing partial allowing their reuse construction is based on to reuse them in the reuse in the same in the same structure prefabricated modules that same structure or in structure or in or in another. are assembled at the site. another. another. Sustainability 2020, 12, 1882 7 of 17

C. Modularizable nature. This refers to the capacity of the structural system to be the result of the union of several modules that interact with each other. Each module must be independent of the rest of the modules and at the same time interact with the others to form a composite structural system (Table5).

Table 5. Modularizable nature assessment rubric.

C. Modularizable nature 1 2 3 4 If the structural resolution If the structural If the structural resolution (primary structure, secondary resolution (primary (primary structure, If the structural structure and auxiliary structure, secondary secondary structure and resolution (primary structure of wall, floor and structure and auxiliary auxiliary structure of wall, structure, secondary ceiling support) is based on structure of wall, floor floor and ceiling support) is structure and modules or components that and ceiling support) is based on modules or auxiliary structure of interact with each other, based on modules or components that interact wall, floor and ceiling formed by elements of components that with each other, formed by support) is not made standard dimensions, and by interact with each elements of standard up of separate joining these modules they other, formed by dimensions, and by joining modules or result in the structural system, elements of standard these modules they result in components that in addition to making it dimensions, and by the structural system, in interact with each possible to replace any of these joining these modules addition to making it other. modules with another and/or they result in the possible to replace any of add more modules without structural system. these modules with another. affecting the rest of the system.

D. Prefabrication/industrialization: Here, prefabrication is understood as the production of constructive elements and/or systems in the factory or workshop, that is to say, prior to the execution of the work (out of place), that will be incorporated later, through a set of operations known as placement. On the other hand, industrialization is the application to the production of buildings in organizational processes (techniques of production engineering), aiming for increasing the productivity of the sector, such as through continuity of production, standardization of products, mechanization, research and experimentation (Table6).

Table 6. Prefabrication/industrialization assessment rubric.

D. Prefabrication/industrialization 1 2 3 4 If some elements used in If none of the elements If all the elements used the structural resolution If all the elements used used in the structural in the structural (primary structure, in the structural resolution (primary resolution (primary secondary structure and resolution (primary structure, secondary structure, secondary auxiliary structure of structure, secondary structure and auxiliary structure and auxiliary wall, floor and ceiling structure and auxiliary structure of wall, floor structure of wall, floor support) are structure of wall, floor and ceiling support) are and ceiling support) are prefabricated and also and ceiling support) are prefabricated or prefabricated. industrialized (in case of industrialized. industrialized. mixed systems).

E. Weight This parameter considers a weight range that takes into account the heaviest and lightest system of the prototypes analyzed, with the intention of closely comparing the heaviness of the structural systems of the case studies and their relationship with the proposed materials and systems. From this range, “quarters of weight ranges” (diﬀerence between the highest weight and the lowest weight divided by four) were assigned for the weights (from 1 to 4 points) of each prototype. To obtain this quantitative data, it was necessary to dismantle and quantify each of the elements that make up the Sustainability 2020, 12, 1882 8 of 17 structural system of each prototype, to later relate it to the weight of each material and thus obtain the weight (Table7).

Table 7. Weight assessment rubric.

E. Weight 1 2 3 4 If the weight of the If the weight of the If the weight of the If the weight of the structural system structural system structural system structural system (primary structure, (primary structure, (primary structure, (primary structure, secondary structure and secondary structure and secondary structure and secondary structure and auxiliary structure of auxiliary structure of auxiliary structure of auxiliary structure of wall, floor and ceiling wall, floor and ceiling wall, floor and ceiling wall, floor and ceiling support) is between support) is between support) is between support) is between 12,826.40 kg to 17,101.87 8,550.94 kg to 12,826.40 4,275.47 kg to 8,550.94 kg 0.0 kg to 4,275.47 kg (first kg (last quarter of the kg (third quarter of the (second quarter of the quarter of the weight weight range of the weight range of the weight range of the range of the analyzed analyzed prototypes). analyzed prototypes). analyzed prototypes). prototypes).

F. Flexibility and adaptability Here, the flexibility and adaptability of the structural system is considered and scored, i.e., the ability of its modules or elements to change their initial configuration and adapt to the different phenomena and complexities of living. Likewise, maximum weighting is granted if, in addition to these qualities, the system considers perfectibility, understood as the capacity of the system to accept different assemblies of other elements to seek to gradually improve it (Table8).

Table 8. Flexibility and adaptability assessment rubric.

F. Flexibility and adaptability 1 2 3 4 If all of the elements used in If some of the elements If all of the elements If none of the elements the structural resolution used in the structural used in the structural used in the structural (primary structure, resolution (primary resolution (primary resolution (primary secondary structure and structure, secondary structure, secondary structure, secondary auxiliary structure of wall, structure and auxiliary structure and auxiliary structure and auxiliary floor and ceiling support) are structure of wall, floor structure of wall, floor structure of wall, floor flexible and the structural and ceiling support) are and ceiling support) are and ceiling support) is system also accepts other flexible, that is to say, flexible and encourage flexible to encourage assemblies of elements or they allow different the total or partial reconfiguration of living components that encourage configurations of the adaptability of the spaces. the perfectibility of living living spaces. prototype. space.

G. Accessibility and availability of the proposed materials This parameter weights the choice of materials for the structural resolution of the prototype from a sustainable point of view. Aspects such as if the materials are indigenous, easy to access and transfer to the site of placement and the availability of the material are considered (Table9). Subsequently, based on the results obtained in the descriptive–qualitative–comparative and quantitative–comparative analyses, a discussion is carried out. Sustainability 2020, 12, 1882 9 of 17

Table 9. Accessibility and availability of the proposed materials assessment rubric.

G. Accessibility and availability of proposed materials 1 2 3 4 If the raw material with If the raw material with If the raw material with If the raw material with which which the elements used which the elements used which the elements used the elements used in the in the structural in the structural in the structural structural resolution were made resolution were made resolution were made resolution were made (primary structure, secondary (primary structure, (primary structure, (primary structure, structure and auxiliary structure secondary structure and secondary structure and secondary structure and of wall, floor and ceiling auxiliary structure of auxiliary structure of auxiliary structure of support) is indigenous and wall, floor and ceiling wall, floor and ceiling wall, floor and ceiling easily accessible and has a short support) is not support) is not support) is indigenous transfer to the prototype site; indigenous nor easy to indigenous, but it is and easily accessible and besides that, its availability access nor has a short easily accessible and has has a short transfer to the (supply) in the local market is transfer to the location of a short transfer to the prototype site. greater than the demand. the prototype. place of prototype site.

3. Comparative Analysis of the Case Study Prototypes

3.1. Descriptive–Qualitative–Comparative Analysis of Structural System Tables 10 and 11 expound the principal parameters that, to a greater or lesser extent, characterized all the prototypes in the competition. It is also inferred that these are parameters that prefabricated and industrialized structural systems must have, because they are qualities and characteristics that do not consider the solutions projected with conventional materials at present. In these tables the structural systems of the study cases are exposed comparatively according to these parameters.

Table 10. Descriptive–qualitative–comparative analysis.

Concept Typology Materiality Main structure based on: Laminated Veneer Lumber Structure resistant to floods and SU + RE House Mixed structure (LVL) beams (floor framing), Trus Joist I-Joist (TJI) for storms, structural integrity in (SD U.S. 2015) (combination of Balloon the floor, wooden columns, LVL beams (covered coastal environment, sustainable (SU) Frame and Steel Frame). framing, TJI joists for roof). and durable. Porch: steel columns, steel beams. Casa del Sol Modular structure, Mixed structure Main structure based on: steel beams, metallic profiles. (SD U.S. 2015) earthquake-proof, easy to (combination of Balloon Substructure: wooden joists. (CS) assemble and transport. Frame and Steel Frame). Auxiliary structure: wooden elements. Structure based on Nexushaus Modular structure, easy frames of Balloon For main structure: 2” 10” beams for wood framing; (SD U.S. 2015) transportation and assembly of Framing style with × pillars and beams steel Bantam cold formed. [NH] components, sustainable. corner elements and steel columns. Modular structure, easy to Structure “Space Frame” For main structure: tubular steel of different diameters, CASA assemble and transport, type, made of steel and OC steel columns; profiles, angles, and steel (SD EU 2014) self-building, which seeks to wooden frames for connections. [CA] optimize the occupation area. interior solutions. For substructure of interior solutions: plywood frames Prefabricated structure, which For main structure: structure of 120 120 mm wooden Renaihouse seeks high performance in an Frame structure of wood × pillars, 9 mm thick plywood (SD EU 2014) earthquake, optimized based on three cores For substructure of interior solutions: 9 mm thick [RE] construction times and easy (urban seeds). plywood portability. The skeleton or main structure is formed by: ground Casa Fénix Light structure, of easy Wooden structure whose footing, wooden footing, “column panel” components (SD EU 2014) progressive modulation and fast basic component is the (structure) and the wall at the same time, floor beams, [FE] assembly. “column panel”. roof beams. Grid structure with dry joints, Aura Project Steel grid divided in which reduces assembly times For main structure: tubular steel, steel angle, (SD LAC 2015) three modules with dry and the generation of waste; corrugated sheet, wood–steel composite profile [AU] joints. based on three modules. Primary structure: IR expanded steel beams and OR Kuxtal Lightweight structure, self-built steel profiles (HSS) for columns and roof structure Structural system “Steel (SD LAC 2015) (assisted construction), modular beams. Framing” style. [KX] and sustainable. Secondary structure: C’formed-purlin profiles. Parapet Substructure: bracings, interior and enclosure walls. Sustainability 2020, 12, 1882 10 of 17

Table 11. Descriptive–qualitative–comparative analysis.

(SU) (CS) (NH) (CA) (RE) (FE) (AU) (KX) Possibility of assembly/disassembly •••••••• Modularizable nature ••••••• Prefabrication •••••••• Industrialization ••••••• Eﬃcacy in placing ••••••• Savings and quickness in construction •••••• LCA consideration ••••• Flexibility •••••• Adaptability •••••• Perfectibility • Accessibility and availability of materials •••••••• Use of indigenous materials • Waste management during construction ••••• Recycling possibility of elements •••••••• Reuse possibility of elements •••••••• is used to indicate the use of this item. • SU + RE House (SU)—Flood- and storm-proof design, minimal use of energy-intensive materials, high-eﬃciency safe system, fully integrated into the coastal setting, sustainable and durable (Figure2). Mixed structure combining “Balloon Frame” and “Steel Frame” (mainly for the portico and external elements).Sustainability 2020, 12, x FOR PEER REVIEW 3 of 19

FigureFigure 2.2. SUSU ++ RE House. SD SD U.S. U.S. 2015.

Casa del SolSol (CS)(CS) –– ModularModular system,system, earthquake-proof,earthquake-proof, transportabletransportable and easy to assemble. Mixed structure: mainly mainly steel steel for the main struct structureure and wood for the substructure and auxiliary structure toto supportsupport ﬁnishesfinishes (Figure(Figure3 3).).

Figure 3. Casa del Sol. SD U.S. 2015.

Nexushaus (NH)—Modular project, easy transportation and assembly of sustainable components (Figure 4).“Balloon Frame” structure with some steel corner posts and beams.

Figure 4. Nexushaus. SD U.S. 2015.

CASA (CA)—Construction system design following basic concepts such as: modularity, light weight, flexibility, self-build, easy assembly and disassembly, transportability, compatibility with other systems and optimal usage of space. Steel “Space Frame” structure combined with wooden frames for interior solutions and finishes (Figure 5). Sustainability 2020, 12, x FOR PEER REVIEW 3 of 19

Sustainability 2020, 12, x FOR PEER REVIEW 3 of 19

Figure 2. SU + RE House. SD U.S. 2015. Figure 2. SU + RE House. SD U.S. 2015. Casa del Sol (CS) – Modular system, earthquake-proof, transportable and easy to assemble. MixedCasa structure: del Sol mainly (CS) – steel Modular for the system, main structearthquake-proof,ure and wood tr ansportablefor the substructure and easy and to assemble.auxiliary structure to support finishes (Figure 3). MixedSustainability structure:2020, 12 ,mainly 1882 steel for the main structure and wood for the substructure and auxiliary11 of 17 structure to support finishes (Figure 3).

Figure 3. Casa del Sol. SD U.S. 2015. Figure 3. Casa del Sol. SD SD U.S. U.S. 2015. Nexushaus (NH)—Modular project, easy transportation and assembly of sustainable componentsNexushaus (Figure (NH)(NH) 4).“Balloon—Modular—Modular Frame” project, project, structure easy easy transportation with transporta some andsttioneel assembly corner and postsassembly of sustainable and beams.of componentssustainable (Figurecomponents4). “Balloon (Figure Frame” 4).“Balloon structure Frame” with structure some steel with corner some posts steel andcorner beams. posts and beams.

Figure 4. Nexushaus. SD SD U.S. U.S. 2015. 2015. Figure 4. Nexushaus. SD U.S. 2015. CASA (CA) —Construction system design following ba basicsic concepts such as: modularity, modularity, light weight,CASA ﬂexibility,flexibility, (CA)—Construction self-build, self-build, easy easy system assembly assembly design and and disassembly,following disassembly, ba transportability,sic transportability,concepts such compatibility as: compatibility modularity, with otherwithlight otherweight,systems systems flexibility, and optimal and self-build,optimal usage ofusage space.easy of assemblySteel space. “Space Steel and Frame” “Spacedisassembly, structureFrame” transportability, st combinedructure combined with compatibility wooden with frames wooden with for framesSustainabilityotherinterior systems for solutions 2020interior , and12, andx solutions FORoptimal ﬁnishes PEER usageREVIEWand (Figure finishes of space.5). (Figure Steel 5). “Space Frame” structure combined with wooden4 of 19 frames for interior solutions and finishes (Figure 5).

Figure 5. CASA. SD Europe 2014.

Renaihouse (RE)—ConstructionTable 10. Descriptive–qualitative–comparative system design based on prefabrication, analysis. transportability, high resistance to earthquakes, light weight, and optimal construction times (Figure6). Wooden lattice structure. Based on threeConcept hubs known as “Urban Seeds”.Typology Materiality Main structure based on: Laminated Veneer Lumber SU + RE Structure resistant to (LVL) beams (floor framing), Mixed structure House floods and storms, Trus Joist I-Joist (TJI) for the (combination of (SD U.S. structural integrity in floor, wooden columns, LVL Balloon Frame and 2015) coastal environment, beams (covered framing, TJI Steel Frame). (SU) sustainable and durable. joists for roof). Porch: steel columns, steel beams. Casa del Main structure based on: steel Mixed structure Sol Modular structure, beams, metallic profiles. (combination of (SD U.S. earthquake-proof, easy to Substructure: wooden joists. Balloon Frame and 2015) assemble and transport. Auxiliary structure: wooden Steel Frame). (CS) elements. Structure based on Nexushaus Modular structure, easy For main structure: 2" × 10" frames of Balloon (SD U.S. transportation and beams for wood framing; Framing style with 2015) assembly of components, pillars and beams steel Bantam corner elements and [NH] sustainable. cold formed. steel columns. For main structure: tubular Modular structure, easy Structure "Space CASA steel of different diameters, OC to assemble and Frame" type, made of (SD EU steel columns; profiles, angles, transport, self-building, steel and wooden 2014) and steel connections. which seeks to optimize frames for interior [CA] For substructure of interior the occupation area. solutions. solutions: plywood frames Prefabricated structure, For main structure: structure Renaihouse which seeks high Frame structure of of 120 × 120 mm wooden (SD EU performance in an wood based on three pillars, 9 mm thick plywood 2014) earthquake, optimized cores (urban seeds). For substructure of interior [RE] construction times and solutions: 9 mm thick plywood easy portability. Casa Fénix Wooden structure The skeleton or main structure Light structure, of easy (SD EU whose basic is formed by: ground footing, progressive modulation 2014) component is the wooden footing, "column and fast assembly. [FE] "column panel". panel" components (structure) Sustainability 2020, 12, x FOR PEER REVIEW 5 of 19

and the wall at the same time, floor beams, roof beams. Aura Grid structure with dry For main structure: tubular Project joints, which reduces Steel grid divided in steel, steel angle, corrugated (SD LAC assembly times and the three modules with sheet, wood–steel composite 2015) generation of waste; dry joints. profile [AU] based on three modules. Primary structure: IR expanded steel beams and OR steel profiles (HSS) for Kuxtal Lightweight structure, columns and roof structure (SD LAC self-built (assisted Structural system beams. 2015) construction), modular "Steel Framing" style. Secondary structure: [KX] and sustainable. C'formed-purlin profiles. Parapet Substructure: bracings, interior and enclosure walls.

Renaihouse (RE)—Construction system design based on prefabrication, transportability, high Sustainabilityresistance 2020to earthquakes,, 12, 1882 light weight, and optimal construction times (Figure 6). Wooden 12lattice of 17 structure. Based on three hubs known as “Urban Seeds”.

Figure 6. Renaihouse. SD Europe 2014.

Casa FFénixénix (FE)(FE)—Construction—Construction system design following basic concepts such as progressive modulation, flexible ﬂexible construction times, quickquick andand easyeasy assemblyassembly ofof components.components. Lightweight (Figure7 7).). WoodenWooden structure structure whose whose basic basic component component is is “panel “panel and and column”. column”.

Figure 7. Casa Fénix. Fénix. SD Europe 2014.

Aura Project (AU) —Based on concepts concepts of of assisted assisted self-build self-build and and housing housing perfectibility, perfectibility, whereby Sustainabilitythe house house is2020 is improved improved, 12, x FOR upon PEER upon REVIEWas as the the family family grows grows (Fig (Figureure 8). 8The). Thestructural structural system system consists consists of a three-6 of of a19 three-dimensional mesh on which the prototype is divided into three transportable modules. A metal, dimensionalwooden and Guaduamesh on bamboo which the structure prototype was developed.is divided into three transportable modules. A metal, wooden and Guadua bamboo structure was developed.

Figure 8. Aura Project. SD LAC 2015. Figure 8. Aura Project. SD LAC 2015. Kuxtal (KX)—Dynamic, evolutionary, economical, innovative, passive and efficient construction Kuxtal (KX)—Dynamic, evolutionary, economical, innovative, passive and efficient system based on concepts such as self-construction, recycling and modulation. Industrially construction system based on concepts such as self-construction, recycling and modulation. manufactured elements are used for easy transport and assembly (Figure9). Simple, lightweight Industrially manufactured elements are used for easy transport and assembly (Figure 9).Simple, and easy-to-build structural system based on easily acquired commercial steel profiles to produce lightweight and easy-to-build structural system based on easily acquired commercial steel profiles to a self-constructible, modular, sustainable system. “Steel Framing” structural system, interiors produce a self-constructible, modular, sustainable system. “Steel Framing” structural system, and finishes. interiors and finishes.

Figure 9. Kuxtal. SD LAC 2015.

Table 11. Descriptive–qualitative–comparative analysis.

(SU (CS (C (RE (FE (K (NH) (AU) ) ) A) ) ) X) Possibility of assembly/disassembly ● ● ● ● ● ● ● ● Modularizable nature ● ● ● ● ● ● ● Prefabrication ● ● ● ● ● ● ● ● Industrialization ● ● ● ● ● ● ● Efficacy in placing ● ● ● ● ● ● ● Savings and quickness in construction ● ● ● ● ● ● LCA consideration ● ● ● ● ● Flexibility ● ● ● ● ● ● Adaptability ● ● ● ● ● ● Perfectibility ● Accessibility and availability of materials ● ● ● ● ● ● ● ● Use of indigenous materials ● Waste management during construction ● ● ● ● ● Recycling possibility of elements ● ● ● ● ● ● ● ● Sustainability 2020, 12, x FOR PEER REVIEW 6 of 19

dimensional mesh on which the prototype is divided into three transportable modules. A metal, wooden and Guadua bamboo structure was developed.

Figure 8. Aura Project. SD LAC 2015.

Kuxtal (KX)—Dynamic, evolutionary, economical, innovative, passive and efficient construction system based on concepts such as self-construction, recycling and modulation. Industrially manufactured elements are used for easy transport and assembly (Figure 9).Simple, lightweight and easy-to-build structural system based on easily acquired commercial steel profiles to produce a self-constructible, modular, sustainable system. “Steel Framing” structural system, interiors and finishes. Sustainability 2020, 12, 1882 13 of 17

Figure 9. Kuxtal. SD LAC 2015. Figure 9. Kuxtal. SD LAC 2015. 3.2. Quantitative–Comparative Evaluation Table 11. Descriptive–qualitative–comparative analysis. The scores obtained in each parameter evaluated are graphed below, and these results are discussed: (SU (CS (C (RE (FE (K (NH) (AU) A. Materiality ) ) A) ) ) X) Possibility of assembly/disassembly ● ● ● ● ● ● ● ● Starting from the fact that all the structural systems studied are composed of wood, steel or mixed elements andModularizable because in this nature parameter the materials● ● that were● used● in the● structural● system● are evaluated, takingPrefabrication as reference the “Red List” developed● ● by the●International ● ●Living ● Future● Institute,● all the prototypesIndustrialization obtained the maximum score● (4 points),● because● ● in this●list these materials● ● are not considered.Efficacy in placing ● ● ● ● ● ● ● Savings and quickness in construction ● ● ● ● ● ● B. PossibilityLCA of assembly consideration/disassembly (joints) and efficiency ● in placement● ● ● ● Similarly, almostFlexibility all the prototypes analyzed meet the characteristic● ● of enabling● their● assembly● and● disassembly, throughAdaptability the use of the relevant unions between● its di fferent● components.● ● Kuxtal● and Casa● Fénix projects didPerfectibility not obtain the highest rating, scoring just 3 points, because their● implementation strategiesAccessibility require and greater availability assembly of materials time for their● components,● ● despite● having● the● characteristic● ● of being modular.Use of indigenous materials ● Waste management during construction ● ● ● ● ● C. ModularizableRecycling possibility nature of elements ● ● ● ● ● ● ● ● The Casa Fénix, Renaihouse and CASA prototypes achieved the highest score, since their structural resolution is based on modules that interact with each other, being made up of elements with standard dimensions; in addition, it is possible to replace any of these modules with another and/or add more modules without affecting the rest of the system. They are followed by the Casa del Sol project with 3 points and then the rest of the prototypes with 2 points.

D. Prefabrication/industrialization In the “Prefabrication/industrialization” parameter, the prototypes Proyecto Aura, Kuxtal, SU + RE House, Casa del Sol, Nexushaus and CASA achieved the maximum score, inasmuch as all the elements that compose their structural systems have these characteristics and also consider standard measures in its design. Casa Fenix and Renaihouse got only two points.

E. Weight The lighter prototype is Nexushaus. As it is located in the ﬁrst quarter of the rubric of evaluation of this parameter described above, it got 4 points. On the other hand, the heaviest projects were CASA and Casa del Sol; they obtained only 1 point, because they were in the last quarter of the evaluation rubric. In between were Aura, Renaihouse and SU + RE House projects with 2 points and Kuxtal and Casa Fénix with 3. Sustainability 2020, 12, 1882 14 of 17

F. Flexibility and adaptability Casa Fénix, Renaihouse, and CASA were the best-weighted projects in this parameter, with 4 points, not only proposing a ﬂexible and adaptable structural system, but also giving a plus when designing a system that allows assemblies of other elements or components providing the perfectibility of the living space. The worst qualiﬁed were Casa del Sol and SU + Re House with 1 point, followed by Kuxtal with 2 points and Nexushaus and Aura project with 3.

G. Accessibility and availability of materials In this parameter, the Renaihouse prototype is the only one that obtained the maximum qualiﬁcation, since the raw material with which the elements used in the structural resolution were manufactured is indigenous, easily accessible and with short transfer distance to the prototype site; in addition, its availability (supply) in the local market is greater than the demand and helps the recovery of the local timber industry. Renaihouse prototype is followed by the Casa Fénix, Nexushaus Sustainabilityand SU + Re2020 House, 12, x FOR projects PEER REVIEW with 3 points and the rest of the teams with 2. 8 of 19 The following graph (Figure 10) exhibits a comparison of the ﬁnal weighting by evaluated Likewise,parameter the of eachprototype prototype with studied,the lowest where score it isis observedCasa del thatSol (built the structural by the University systems of of the California, best rated Irvine,projects Chapman are Nexushaus University (proposed and Irvine bythe Valley University College) of with Texas 19 atpoints. Austin and Technische Universitat Munchen) and Renaihouse (from the University of Chiba in Japan) with 24 points out of 28 possible. Likewise, the prototype with the lowest score is Casa del Sol (built by the University of California, Irvine, Chapman University and Irvine Valley College) with 19 points.

KUXTAL

PROYECTO AURA

CASA FÉNIX

RENAIHOUSE

CASA

NEXUSHAUS

CASA DEL SOL

SU + RE HOUSE

0 4 8 12 16 20 24 28 MATERIALITY ASSEMBLY / DISASSEMBLY MODULABILITY PREFABRICATION / INDUSTRIALIZATION WEIGHT FLEXIBITY / ADAPTABILITY

ACCESSIBILITY / AVAILABILITY OF MATERIALS Figure 10. Result across this methodology. Figure 10. Result across this methodology. Finally, the following ﬁgure shows a comparison of results between the weights obtained by the caseFinally, study prototypes the following in this figure proposed shows methodology a comparison vs. of theresults qualiﬁcations between the obtained weights in obtained their respective by the caseeditions study of prototypes the Solar in Decathlon this proposed competition methodology (Figure vs. 11 the). Toqualifications achieve a moreobtained objective in their comparison, respective editionsthe results of the are Solar expressed Decathlon in percentages, competition considering (figure 11). the To maximum achieve a scoremore ofobjective each edition comparison, as 100% the (in resultsthis methodology are expressed 28 in points, percentages, in the SDLACconsidering 100 points,the maximum in the SDEUscore of 80 each points edition and as in 100% the SDEEUU (in this methodology100 points). 28 points, in the SDLAC 100 points, in the SDEU 80 points and in the SDEEUU 100 points).

Rating in the Solar Decathlon Rating in this methodology 100 95 93 92 91 90 85.71 85.71 85 82.14 82.14 80 75.00 71.43 71.43 67.86

Figure 11. Scores obtained in this methodology vs. scores obtained in the SD. SustainabilitySustainability 20202020,, 1212,, 1882x FOR PEER REVIEW 155 of 1718

Rating in the Solar Decathlon Rating in this methodology

100

85.71 85.71

82.14 82.14

75.00

71.43 71.43 67.86

Figure 11. Scores obtained in this methodology vs. scores obtained in the SD. Figure 11. Scores obtained in this methodology vs. scores obtained in the SD. From the previous graph it follows that the structural system of the CASA project was the best valuedFrom in its the respective previous competencegraph it follows of the that SD, the while structural the Kuxtal system prototype of the CASA was the project onethat wasreceived the best thevalued lowest in its rating. respective These competence results are not of coincidentthe SD, while with the the Kuxtal weighting prototype obtained was bythe the one projects that received shown inthe this lowest methodology. rating. These results are not coincident with the weighting obtained by the projects shown in this methodology. 4. Discussion and Conclusions 4. DiscussionFrom the and comparative Conclusions quantitative evaluation, it is concluded that the Renaihouse prototype is one ofFrom the bestthe comparative scored because quantitative its structural evaluation, solution it is is designed concluded for that an the emergent Renaihouse housing prototype model inis caseone of the disasters, best scored consequently, because theits structural accessibility, solution availability is designed and materiality for an emergent are optimal housing for its model context. in Incase the of same disasters, way, its consequently, assembly and the dismantling accessibility, and availability rapidity in and placement materiality in site are is possible optimal due for its to prefabricatedcontext. In the modules same way, of easyits assembly transport an that,d dismantling once placed, and can rapidity be adaptable in placement and perfectible. in site is possible due toLikewise, prefabricated the Nexushaus modules of prototype easy transport is another that, once of the placed best weighted, can be adaptable because and it minimizes perfectible. the componentsLikewise, and the spaces Nexushaus of the home,prototype is designed is another to optimizeof the best the weighte materialityd because and provide it minimizes lightness, the includescomponents elements and spaces of high of the industrialization home, is designed and practicalityto optimize ofthe assembly, materiality resulting and provide in a structurallightness, solutionincludes of elements fast and of easy high transportation. industrialization and practicality of assembly, resulting in a structural solutionAfter of the fast descriptive-qualitative–comparative and easy transportation. analysis, the characteristics of the prototypes and structuralAfter solutionsthe descriptive worsened-qualitative by their–comparative environmental analysis, impacts the withcharacteristics respect to of the the qualities prototypes of those and withstructural less deducedsolutions impact. worsened That by istheir to say, environmental aspects such impacts as: optimize with respect the living to the surface qualities as muchof those as possiblewith less (dimensions deduced impact. and reduced That is areas),to say, useaspects lightweight such as: elements, optimize considerthe living the surface modulation as much of its as componentspossible (dimensions for easy transportation,and reduced areas), optimize use assemblylightweight and elements, assembly consider times, and the propose modulation accessible of its andcomponents available for materials easy transportation, (indigenous) optimize preferably. assembly In addition and toassembly managing times, waste and during propose construction accessible and theavailable end of materials life of the (indigenous) elements used, preferably these are. In fundamental addition to characteristicsmanaging waste that during must beconstruction taken into accountand the end if the of aim life isof tothe design elements and used, propose these structural are fundamental systems whose characteristics impacts associatedthat must be with taken the into life cycleaccount of theif the system aim is are to lower.design and propose structural systems whose impacts associated with the life cycleFrom of the the system methodology are lower. of quantitative–comparative evaluation of the Solar Decathlon prototypes discussedFrom in the this document, methodology it can of be quantitative deduced that–comparative the methodology evaluation for evaluating of the structural Solar systemsDecathlon of theprototypes projects presented discussed is in merely this d subjective,ocument, soit can it is fundamentallybe deduced that important the methodo to objectifylogy forit, as evaluating proposed instructural this document. systems It of is the necessary projects to presented have a methodology is merely subjective, that by means so it ofis afundamentally set of criteria quantitatively important to assessesobjectify (thatit, as score proposed is awarded) in this thedocument. prefabricated It is necessary/industrialized to have structural a methodology systems andthat theirby means solutions of a toset the of di criteriaﬀerent problems, quantitatively considering assess social,es (that climatic, score geographical is awarded) contexts the prefabricated/industrialized and natural and economic resources,structural among systems other and factors their thatsolution intervenes to depending the different on the problems location, and considering/or proposal social, of the climatic, project site.geographical It is also considered contexts and essential natural to and take economic into account resources, and regulate among in aother concrete factors way that the intervenesolutions proposeddepending by on each the team, location including and/or the proposal design, of composition, the project transport,site. It is also use andconsidered end of lifeessential of each to of take the into account and regulate in a concrete way the solutions proposed by each team, including the Sustainability 2020, 12, 1882 16 of 17 elements that materialize the prototype. Also, the deliverables (plans, memories, construction details, design intentions, etc.) should be generated in the form of a constructive manual, and this in turn should be published and available to any professional or actor involved in the construction, so that, with this, the innovations proposed in the competition are disseminated and taken into account as adaptable and valid solutions. All the above are proposed in search of more sustainable projects. Finally, the proposals and results from the Solar Decathlon contest in the context analyzed are clearly a point of reference for technological innovations and a meeting of applicable and repeatable knowledge in construction. However, it is necessary to continue working on adjusting the bases and tests of the competition. The implementation of other methodologies for evaluation and comparison of prototypes of the competition, such as the one proposed here, is necessary. The need to develop a quantitative–comparative analysis of the environmental impacts associated with the construction of the structural system of the prototypes in the Solar Decathlon is inferred, because there is no test which weights these impacts, and this evaluation could be implemented based on the parameters used in the qualitative-comparative analysis here exposed and developed.

Author Contributions: Conceptualization, all authors; methodology, all authors; validation, all authors; formal analysis, all authors; investigation, all authors; writing—Original draft preparation, all authors; writing—Review and editing, all authors; supervision, all authors; project administration, all authors. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The Authors would like to thank the Kuxtal (Instituto Tecnológico de Monterrey—Mexico) and Aura (Universidad de Sevilla, Spain) teams who both participated in the 2015 edition of the Solar Decathlon Latin America and Caribbean, held in Santiago de Cali (Colombia), for all the data provided for this article. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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