Starting from the incorporation of SDGs into the design process, the results obtained in SDLac15 (First Prize Communication, Marketing and Social Conscience, First Prize Comfort Conditions, Third Prize Engineering and Construction, Third Prize Innovation and Runner-up Prize Architecture), based on the previous Millennium Goals, demonstrate that the previous approach is based on a project design strategy [49] distinguished with numerous awards and validated by the design results of the project itself, both urban and building-related. However, in urban matters, many of the proposals are not sufficiently defined or appropriate to these new SDGs. Therefore, it is necessary to develop an 'Aura Method' that allows us to consolidate, with the necessary tools, the process that ensures that these SDGs are explicitly referenced and take shape in the final decisions of project design. Health suitability has recently become a priority in terms of approaching the SDGs, and the Aura Method reinforces the importance of this transversal but crucial aspect as the basis for improving resilience in our building environment and cities.

#### 2.1.1. Generation of the Aura Matrix

The Aura Matrix is a practical, graphically expressed tool for relating concepts that allows the SDGs to be approached in a systematic and direct way, as well as very quickly, with the requirements defined by the SD competition for the completion of its 10 tests. This matrix is a key tool of the Aura Method and is generated for each specific case during its development. Its generation process for the specific case of SDLac19 is explained below.

2.1.2. Phases of the Aura Method

The Aura Method, designed to systematize a way of dealing with the design of an architectural and urban project that allows the SDGs to be rigorously included, follows the scheme shown in Figure 2 and consists of the following phases:

**Figure 2.** Aura Method diagram. Source: the authors.

The complete development of these phases has made it possible to generate a project for SDLac19, whose characteristics and design decisions explicitly respond to the SDGs, as can be seen below.

#### *2.2. The Aura Method Application*

2.2.1. Framework Definition: The Solar Decathlon Competition, Analysis and Requirements

The SD competition is centered around the 10 tests mentioned above: Architecture; Energy Efficiency; Engineering and Construction; Comfort, Marketing and Communication; Electrical Energy Balance; House Functioning; Innovation; Urban Design; Affordability; and Sustainability.

The urban issue is part of the initial design phase of the project, and the prototype must be framed within it. However, the prototype construction phase in the Villa Solar requires the adaptation of the urban building proposal to a single-family housing prototype [50] as an experimental case. The definition of the place where the specific urban proposal is made is left to the teams that enter the competition and is always justified based on the needs detected in the city.

As can be seen, the premises and design requirements of the competition itself are perfectly in line with many of the issues defined by the SDGs and are integrated as dynamics or project objectives by the Aura Strategy of the Solar Decathlon Team of the University of Seville. The complexity [51] lies in the multitude of premises that address different scales of action, involve numerous and diverse agents and must respond to the regional, territorial and urban components of the site. To this end, the SDLat19 proposal begins by systematizing the scales of action into: individuals, dwellings, neighborhoods, communities and city. The agents involved are systematized into: citizens, social partners, technicians and politicians. Finally, the regional determining factors are systematized by defining four relevant strategies: the construction and/or improvement of social housing in terms of habitability and health, the increase in density, the use of a rational use of environmental resources and the promotion of regional relevance or progress, the latter being understood as sustainable development and not just economic growth.

#### 2.2.2. Training and Awareness of Agenda 2030 and SDGs

The Aura strategy defined by the present research project is grounded in a global and transdisciplinary university framework that involves the whole University of Seville. Based on this approach, various actions are designed to raise awareness to the SDGs, with the participation of the coordinating members of the Aura Team. These actions, proposed at the university level as an Awareness and Training Program on the new Agenda 2030, give rise to various training events. All these actions are used for the training of the Decathlete students who participate in the Aura project. In particular, the Awareness Days 'The University of Seville for the Sustainable Development Objectives' are the framework in which the students participate in various forums and transdisciplinary working groups, according to their interests and fields of specialization. The Aura team is made up of students from different disciplines [52] and not only architects and engineers, as was traditionally the case. Therefore, the SDGs and their transdisciplinary scope encourage exchange, global and holistic reflection and cooperation among students of the team itself.

The Conferences are held in the six campuses of the University of Seville, with 62 specialized conferences on the most varied topics, covering the spectrum of the 17 Sustainable Development Goals and complemented by subsequent debates. The entire Aura Team also participates in the round tables held at the School of Architecture, whose objective is to deepen the understanding of objectives 9—'Industry, innovation and infrastructure. Building resilient infrastructures, promoting inclusive and sustainable industrialization and fostering innovation'—and 11—'Sustainable cities and communities. To make cities and human settlements inclusive, safe, resilient and sustainable', more specifically with regard to architectural-engineering solutions with a direct impact on the framework of the experimental competition under development—and 'Goal 3: Ensure healthy lives and promote well-being for all at all ages', focused on the great challenges that are being addressed today. These round tables are approached from four thematic areas: production, territory, city and community; and during them, the debate is coordinated by an expert in the field, bringing together both decathlete students as representatives of the local and regional administration and teachers and research experts, enriching the speeches and reflections and outlining practical approaches to the various issues. The conclusions of these debates constitute the basis on which the strategic lines of integration of the SDG of the Aura Project are organized, which allow the concepts transmitted from the Objectives of Sustainable Development to be approached in a broad and inclusive manner.

2.2.3. SDGs Workshop Development and Generation of the SD-SDGs Aura Matrix Interrelationship

After the awareness development process, a workshop is held with the aim of defining the strategic lines of integration of the SDGs in the design of the architectural project of the Aura Team for the SDLat19. This workshop is developed in several phases: Brainstorming session; Definition of priority strategic lines; Categorization and organization of the strategic lines in thematic areas. Decathlete students as well as numerous expert teachers in different specializations and disciplines and the teaching staff who are members or collaborators of the Aura Team attend the workshop. The workshop lasts for six hours, the first two being dedicated to brainstorming and debating ideas, based on the previous approach defined by the Aura Conceptual Strategy, that includes the local premises of the context in Cali, Colombia. The following three hours are dedicated to the construction of the Aura

Matrix, that relates the 17 SDGs to the 10 specific tests of the Solar Decathlon competition, by defining the strategic lines. Finally, the last hour is dedicated to the categorization of these lines in the seven thematic areas defined by the Aura Project. It is relevant to indicate that it is the decathlete students who make the final decisions regarding the strategies and their categorization, with the help and tutoring of teachers and experts, and not the other way around. This dynamic allows the students themselves to develop their own priorities [52] when defining the design of the Architectural Project they are developing, so that they constitute unrenounceable requirements that nourish and condition the Project and not mere declarations of intent without further development.

After the development of the workshop, specialization groups are established within the Aura Team to work on the most relevant issues and their application to the proposal.

#### 2.2.4. Generation of the SD-SDGs Aura Matrix Interrelationship

The matrix tool that enables the SDGs to be related to the project design proposal for the SDLat19 competition is built by defining the 28 strategic lines through the mentioned methodological process of awareness-raising, interiorization, conceptual debate and proposal of the priority strategies that will define the project. This matrix (Figure 3) allows us to verify during the debate and decision making about the strategic lines that all aspects are present and have been taken into account.

These 28 strategic lines, grouped into seven topics (Figure 4), constitute the design basis of the SDLat19 project. Design decisions based on them define the formulation of potential situations of habitability, in terms of comfort and health, and a more sustainable management of the urban space. The architects cannot decide for the user-citizen, but they can design the appropriate conditions of habitability and spatial quality, as well as a more sustainable management, which will incite an improvement in the user-citizen's quality of life [41].

#### 2.2.5. Development of the Aura Proposal for the SD 2019 Latin America Competition

The design process of the Aura Proposal SDLat19 starts from the 28 strategic lines developed thanks to the Aura Method, and is part of the first stage of the process defined by the competition itself and adopted by the Aura Team. Thanks to the involvement of experts and a cross-discipline approach, to the integrated curriculum approach [52] and to the holistic approach provided by the Aura Method, the project design process incorporates educationally the explicit translation of the SDGs into architectural design decisions.

**Figure 3.** Aura Matrix, 28 strategic lines grouped into seven topics (each with a different color). The numbers inside the triangles indicate the number of specific strategies within the same topic. Source: the authors.

**Figure 4.** Example of a scheme for checking requirements and relations defined from the Aura Matrix for every strategic line, in this case four life quality strategic lines. Source: the authors.

#### **3. Results**

#### *3.1. Aura SD Latin America Project 2015*

The Solar Decathlon Latin America and Caribbean competition took place in Santiago de Cali (Colombia) in December 2015. For the first time in the competition, the characteristics of social housing, high-density construction, rational use of natural resources and regional relevance were required, guiding the proposals toward a sustainable social housing solution in Latin America.

The city of Santiago de Cali has a large housing deficit, and the macroproject area of the National Social Interest for the Eco-city of Navarro, a possible area of expansion of public property, has been selected for the development of the proposal [53]. The model of urban growth of the city proposed for Eco-Navarro consists in an organic development where an organized urban fabric will be developed and diluted in a natural space. Thus, the starting point emerges from the edge condition of this location, a meeting point between the city consolidated through the commune 15 and the natural environment of the wetland of the Corregimiento Navarro. The aim is to turn it into a support for an efficient and differentiated habitability (eco-neighborhood) for all the inhabitants of Cali, responding to its favorable and unfavorable conditions. The team aims to tackle the need to provide a solution to the transition space (Eco-Navarro) generated between the city and the eco-park.

Different modes of occupation and relationship with the territory are established through different densities of occupation, which respond to the diversification of neighborhood units (communities) and their location in specific enclaves of the area, attending to different relative and strategic positions in relation to that edge of the city. In each case they have their own articulation elements: a connection with existing or new infrastructures (jetties), treatments of the intermediate spaces between the room, the community and the urban sector to which they belong (social gardens, cooperative workshops, proximity commercial areas, leisure and health points).

The concept of the Equipped Park emerges as a cord, the backbone of the city. Different individual green areas will appear and give rise to communities. These communities will alter the dimensions of the Equipped Park.

The proposal sets in motion a process in which the occupation of this territory, a unique place in the city of Cali, and the traditional and emerging ways of Cali lifestyles go together. The aim is to achieve an efficient housing development based on an agreement between the social interests of various communities and the place itself, preserving its nature, solving its dysfunctions and enhancing its activity in relation to the city and the citizens of Cali. To this end, certain social programs for the promotion and acquisition of housing in Corregimiento Navarro and a mixed program for the rental of social housing and workshops on public promotion premises are proposed as complementary measures. A sustainable city is not only based on the creation of communities in which buildings are sustainable in terms of energy consumption, but also on needs and an economy that allow for the personal development of individuals, linked to the generation of activity and social programs to avoid social exclusion.

#### *3.2. Aura SD Latin America Project 2019*

On this occasion, the project is proposed for the district of Siloé, in Cali, Colombia, due to the problems and deficiencies found there, which make it an object of study. It is a self-built district, which allows for the subsequent extrapolation of the Aura Strategy to other situations. The proposed solutions aim to make Siloé a sustainable social and healthy habitat for everyone.

The main innovation of the proposal is that, in this case, we start from a reality that has already been built. Instead of expanding the city beyond its limits or demolishing districts to build them from scratch, the urban fabric is improved with participatory decisionmaking strategies. The concepts of reuse and recycling of what has already been built are the foundations of the Aura 3.1 proposal. The project starts from the idea of transforming an existing base through fragmented objects and unfinished actions. Thus, the convenience of thinking about interventions made up of fragments as a more realistic and viable option is claimed, as opposed to the unfeasibility, in the current socioeconomic context, of a total renovation of what has been built. This way of intervening, through fragments, will allow for the transformation of a deficient, unhealthy and obsolete starting situation, which no longer responds to current requirements, through microactions that effectively resolve concrete questions linked to contemporary ways of living.

The focus of the approach at the general level arises from the strategy of recovering and valuing the socio-ecosystem support underlying the same neighborhood. To do this, we must work with the 'neighborhood' ecosystem in terms of controlling energy cycles and material resources, and complement it with an inclusive social management strategy that allows its development to become more sustainable over time.

We value the underlying ecosystem, starting from the local water system as a network that allows us to close fundamental material cycles and link them to local energy management by improving both urban and building habitability in terms of comfort and health, linked to climate adaptation and the use of natural energies.

In terms of energy management, the fundamental regenerative strategy is urban naturalization with native species. This strategy allows us to improve air quality, contributing positively to health, to control solar radiation and to reorganize the water cycle, by improving the general habitability of the urban space and the buildings.

In terms of material cycle management, the work is done mainly on the water and soil. Soil management is carried out respecting the building and urban pre-existence, but specifically regenerating those representative points that allow for an autonomous dynamic leading to a subsequent regeneration of the neighborhood.

For an inclusive social management strategy, the services generated from the two previous managements are ultimately defined by the users through participatory strategies, whose nerve centers are the 'Digital Creation Civic Centers', based on the proposals previously defined in terms of health, training, social development and cultural identity.

The 'Aura 3.1' building rehabilitation proposal is configured from a series of specialized devices (fragments/gadgets) capable of coupling to obsolete buildings, which

need to be transformed to meet the new living needs of contemporary society. These gadgets are designed, projected and built in the Digital Creation Civic Centers, with citizen participation and with the resources of the nearby industrial fabric. In this way, products and sub-products from the environment are used, promoting recycling and generating, in addition to jobs, the appropriation of the actions by the people of the neighborhood.

These fragments could be included in the following groups:

The city is reactivated through small interventions, so the economic cost compared to a newly built project is significantly lower.

#### **4. Discussion**

#### *Comparison of Results between the Aura Solar Decathlon Latin America and Caribbean Projects 2015 and 2019*

Once the process has been analyzed by comparing the results obtained in terms of the conceptualization of urban architectural design and the design of the specific urban proposal in relation to the SDGs framework, several conclusions can be established.

From a conceptual point of view, the proposal for SDLat2019 is more appropriate, daring and innovative, since it assumes the built heritage as an undeniable base on which to work, immediately stopping the depredation of the territory with the increase in the extension of the urban fabric. On the other hand, this strategy highlights the value of the urban landscape made up of the most disadvantaged neighborhoods, which are abundant in the Latin American context, and makes it possible to channel their opportunities in terms of greater sustainable development [2], despite their initial differential situation [31].

Both proposals, SDLat15 and SDLat19, improve land use conditions regarding more intensive building densities needed to promote a more compact city and, with it, the advantages in terms of urban metabolism and mobility. The difference lies in the level of social commitment, which in the second case is more in line with an improvement in the social fabric of the involved community.

Both proposals significantly include and adequately resolve energy, material and resource management, linking it in both cases to the management of the supporting ecosystem. The improvement in the SDLat19 proposal lies, once again, in the potential social use, both educational and professional, linked to the management of these resources. This potential social use reinforces the resilience of the neighborhood, not only by improving health aspects related to physical comfort but also by improving psychological comfort, empowering citizens and creating a more creative, resilient and healthy environment [48].

The achievements related to the SDGs that can be drawn from the decisions of the urban architectural project design of both proposals are defined below (Table 1).

**Table 1.** Comparative results of SDLat15 and SDLat19 for each SDG.

It can be seen from the obtained results that the applied methodology, and therefore the defined Aura Method as a process and the Aura Matrix used as a tool, have involved a transformation and an improvement of the design results obtained for the SdLat19 competition. The approach has been consolidated, but the method has allowed, in addition, for the specific definition of a process design that internalizes the SDGs and provides specific responses to them, as potential opportunities provided by the urban city design. The Aura Matrix is an innovative graphic tool that provides a holistic visualization of the whole situation and promotes complex decision making in a simple way, going further than previous partial approaches based on urban form [14] or general management policies [11]. Thus, the main goal of this research has been achieved and constitutes a step forward regarding new and growing practical and specific approaches that introduce the SDGs concept into architectural design practice and education [15,52,54]. The approach has allowed for the introduction of environmental as well as economic and social aspects, such as those linked to citizen participation [55], an achievement that finds its justification and support in the trans-disciplinary field of the urban approach.

With this methodology, the students have also been able to train autonomously, learn how to work in a team, join multidisciplinary teams and face problem-solving situations [2]. On the other hand, the importance given to the processes of participation and citizen empowerment in terms of governance, thanks to the method itself, constitutes a life learning process for students, beyond the architectural and urban planning discipline, and prepares them to be technicians with greater sensitivity and more competent to deal with SDGs in any personal or professional situation in which they may find themselves in the future, thus responding to the requirements defined by the Higher Education Sustainability Initiative (HESI) [27].

The present study has found a field of educational experimentation of great interest within the framework of the Solar Decathlon competitions [50,52]. However, the process defined as Aura Method and the Aura Matrix tool must be adapted, and their educational capacity analyzed in connection with the Architecture Degree Courses and the disciplines involved. It is necessary to continue research on educational issues and analyze and verify the possibilities that this methodological strategy and this tool—or others that may derive from it—can bring to everyday teaching [56], in order to guarantee the correct transversal incorporation of the SDGs in the curriculum of the universities [52] and in everyday professional practice [57].

#### **5. Conclusions and Possible Extrapolations**

The validity of the process, which managed to define a method with excellent results, the richness of the innumerable interdisciplinary and transdisciplinary situations presented

along the way, and even the two-way learning between teachers and students, make this educational experiment an innovative demonstration of the translation of SDGs into architectural design project decisions, which are coherent with the current challenges we face in terms of health in particular and in terms of sustainable development of our cities in general.

Likewise, the framework of the experiment represented by the Solar Decathlon Competitions is stimulating as an opportunity for the students to get in touch with the most up-to-date concepts in the field developed in other universities and with the possibility of exchanging concerns, ideas, concepts and materializations. Fortunately, interesting international competitive initiatives targeting higher education students from all over the world have emerged in recent years, such as the Blue Award [58], the Lafarge Holcim Awards for Sustainable Construction [59], the Architecture at Zero Competition [60], the Fassa Bortolo International Prize for Sustainable Architecture, on its 13th Edition [61], the 2020 ASHRAE Design Competition [62] or the Reinventing Cities Competition [63]. Some of these competitions, such as the one presented here, provide an exceptional framework for the exchange of information and an effective forum for the transmission of knowledge and idealizations generated in the academic world.

This proposed method and tool constitute a working base for research in educational matters, which can be extrapolated to all types of international competitive initiatives, such as those described above, since its adaptability is immediate and simple. The Aura Matrix tool is a reference in terms of the translation and applicability of complex and interdisciplinary concepts to the architectural design decisions of the discipline. Its application must be accompanied by a solid and rigorous educational process defined by the Aura Method, which encourages researchers not only to work on the visibility and development of technical knowledge but also to continuously put potential design decisions in relation to the perceptions of transversal disciplines, conjunctural problematic situations such as the current pandemic and the changing needs and priorities of citizen collectives.

This initiative should serve as a starting point to gradually bring about a change in the approach to university teaching methodology, which should not only be adapted to the reality of the profession, but also aligned, like other administrations, with the requirements launched by international organizations, such as the 2030 Agenda and the 17 SDGs.

From the design point of view, even outside the academic field, the incorporation of the SDGs in the development of architectural and urban planning projects is a tool for sustainable and healthy design, an alternative to official sustainability certifications (BREEAM, LEED, VERDE, etc.) and differentiated by its more global nature, which presents an opportunity worldwide to reduce development inequalities between countries and contribute to the fulfilment of the 2030 Agenda.

**Author Contributions:** All authors have contributed equally to the investigation and final manuscript. conceptualization, R.H.-L., M.L., M.B.-J. and M.T.G.; methodology, R.H.-L., M.L., M.B.-J. and M.T.G.; validation, R.H.-L., M.L., M.B.-J. and M.T.G.; writing—original draft, R.H.-L., M.L., M.B.-J. and M.T.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This article is the result of a study in item FADIN 4.0, within the Research support program of the Campus of International Excellence Andalucía TECH, and was backed by the Government of Andalusia (Regional Ministry of Economy, Knowledge, Enterprise and University). The authors are grateful for the support.

**Acknowledgments:** The authors want to acknowledge all members of the Solar Decathlon Team of the University of Seville.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

## *Article* **Contribution of Roof Refurbishment to Urban Sustainability**

#### **Ángel Pitarch, María José Ruá \*, Lucía Reig and Inés Arín**

Department of Mechanical Engineering and Construction, Jaume I University, CP12071 Castellón, Spain<EMAIL_ADDRESS>(Á.P<EMAIL_ADDRESS>(L.R<EMAIL_ADDRESS>(I.A.)

**\*** Correspondence<EMAIL_ADDRESS>
Received: 10 September 2020; Accepted: 25 September 2020; Published: 1 October 2020

**Abstract:** Achieving sustainable urban environments is a challenging goal—especially in existing cities with high percentages of old and obsolete buildings. This work analyzes the contribution of roof refurbishment to sustainability, considering that most roofs are currently underused. Many potential benefits of refurbishment can be achieved, such as the improvement of the energy performance of the buildings and the use of a wasted space for increasing green areas or for social purposes. In order to estimate the degree of the improvement, a vulnerable area in Castellón (east Spain) was selected as a case study. A thorough analysis of the residential building stock was undertaken. Using georeferenced information from the Cadastral Office we classified them according to typology, year of construction and roof type. Some refurbishment solutions were proposed and their applicability to the actual buildings was analyzed under different criteria. The theoretical benefits obtained in the neighborhood such as energy and carbon emissions savings were evaluated, together with the increase of green areas. Moreover, other social uses were suggested for neglected urban spaces in the area. Finally, a more accurate analysis was performed combining different solutions in a specific building, according to its particular characteristics.

**Keywords:** urban regeneration; roof refurbishment; energy performance

#### **1. Introduction**

The 11th Sustainable Development Goals (SDG) proposed by the United Nations, focus on cities and sustainable communities to make cities inclusive, safe, resilient and sustainable. To this end, in recent years, many policies have been designed.

The European Union—through the energy performance directives of buildings (EPBD) and their transpositions into the national regulations of State Members—actively works to reduce both carbon emissions and the energy used in buildings. From the first Directive established in 2002 [1] to date, requirements have become significantly stricter [2–4] to accomplish reduction targets (UE key targets for 2030: at least 40% cuts in greenhouse gas emissions from the levels in 1990, 32% share for renewable energy and improved energy efficiency). Currently, the EPBD establishes that all new buildings constructed from 2021 (public buildings from 2019) must be nearly zero-energy (NZEB). As defined in Article 2 of EPBD2010/31/UE, NZEB means a building with very high-energy performance. Moreover, most of the energy required must be covered by renewable sources (sunlight, wind, rain, etc.), including those produced on-site or nearby, and nearly zero or very little energy must be provided by non renewable energy sources (essentially coal, petroleum and natural gas).

Although this is a very positive initiative to improve the building stock's sustainability, it is only applicable to new buildings, and there is a vast number of old and obsolete buildings in terms of thermal properties. According to the data reported by the Spanish National Statistics Office (INE) [5], approximately 54% of existing buildings were built before 1980, when there was still no regulation for

the thermal performance that buildings should present. The first standard that regulated the thermal conditions that buildings should meet came into force in 1979 [6] and established quite relaxed thermal requirements. In 2006, the technical building code (CTE, standing for Código Técnico de la Edificación in Spanish) came into force in Spain [7], with new regulations aligned with the European EPBD. The requirements set out in the CTE have been progressively reviewed and updated to date so that, in line with the EPBD, the basic document on energy saving (DB–HE, through Royal Decree 732/2019) aims to build NZEB. However, as reported by the INE and according to the Spanish Government's updated data [8], almost 92% of existing buildings were built before 2006, prior to the CTE being implemented, which means that the contribution of the whole building stock to the NZEB target is minimum. Hence the energy refurbishment of existing buildings is crucial to improve the general energy performance of the building stock. To do so, different refurbishment options may be selected and combined to optimize their potential.

Besides the thermal requirement regulations for buildings, norms on roofing-load capacity should be checked to analyze their construction solutions and buildings' structural capacity should also be observed to specifically calculate overloads. Roldan [9] analyzed the building standards in Spain from the pioneering MV-101/1962 perspective (Decree 195/1963, 17 January). Since then, the overload for roofs of residential buildings has remained at 1 kN/m2 and 2 kN/m2 for non-walkable and walkable roofs, respectively, according to consecutive standards: NBE-AE/88 (Decree 1370/1988, 11 November), repealed by CTE-DB SE-AE-06 (Royal Decree 314/2006, 17 March and the 2008 and 2009 updates).

Logically as buildings are already built, applying passive design measures is quite limited, and energy improvement mainly depends on refurbishing the thermal envelope and using very efficient facilities. As improving the thermal envelope lowers energy demand, this should be the first step when undertaking energy refurbishment interventions. However, this is not what happens under actual conditions due to the high economic cost of refurbishment, usually with a long-term investment return. Therefore, non-economic arguments, such as environmental and social benefits linked with refurbishment, would support interventions.

Nowadays, cities are composed of different typologies of residential buildings, most of which were built in the 20th century and some in the 21st century. Their features are conditioned by many factors that can influence a region's urban development, such as historic and political events, regulatory frameworks (new legislation coming into force, general urban plans, etc.) and socio-economic factors (wars, migratory movement from rural to urban areas or new construction and material techniques emerging). The IEE Project "Typology Approach for Building Stock Energy Assessment" [10], devised with the collaboration of 15 partners from European countries, differentiates four main typologies in the Spanish building stock, which are: single-family house, terraced house, multi-family house, apartment block. The Valencian Institute of Building (IVE), which was responsible for the project in Spain, developed a guide which differentiated three climate regions and six construction periods (which depended on normative evolution). Therefore, homogeneous construction solutions were inferred for each period: <1900, 1901–1936, 1937–1959, 1960–1979, 1980–2006, >2006 [11]. As observed by Martín-Consuegra et al. [12], the analysis of the building regulations in force during the different time periods provided quite an accurate idea of the characteristic constructive features of the year of construction.

#### *Objective and Main Conclusions*

The present work focuses on the potential benefits offered by the refurbishment of roofs in residential buildings. To do so, constructive solutions were examined to analyze possible refurbishment solutions and the potential achieved benefits. Technical aspects, such as energy performance improvement and its profit, were estimated together with some externalities, such as social benefits linked with the enjoyment of a usually underrated and underused part of the building. This work aims to shed some light on the potential role of roofs in the sustainability of the urban environment.

As summarized by Braulio [13], three periods can be differentiated in Spain according to the construction solutions employed in roofs. Buildings constructed before 1940 generally used timber beams and wattle suspended ceilings in sloping roofs, with Catalan-style ventilated systems on flat roofs. The 1940–1979 period was characterized by the introduction of new materials, such as reinforced concrete, which provided new structural options (new slabs with concrete joists and ceramic or concrete blocks). Flat roofs became more popular during this period, when lightweight concrete was used to form the slope of roofing systems and waterproof materials were introduced. From 1980 onward, roofing systems have continuously evolved to the much more complex systems that can be currently used today, which are composed of different materials that fulfill diverse functions like drainage, waterproofing, thermal insulation, etc.

Although it is more difficult to establish such progressive evolution in roof use terms, in the beginning roofs were also employed for social life purposes. This provided homes with more protection from both weather agents and invading attacks. As explained by Graus [14], in pre-industrial societies a roof always embraced many uses. Given lack of space, the roof emerged as an outdoor room that allowed multiple purposes, such as a better use of space for a settlement on steep mountain slopes, drying grain, hanging food, sleeping on hot nights or even celebrating weddings. With time, social life moved to streets and roofs began to be left aside and even ceased being considered a useful space in the vast majority of cases. Although only the protective function of building roofs is generally valued today, sustainability development trends seek to optimize already built spaces instead of generating new urban expansions. Roofs must be seen as spaces that offer sustainable opportunities to improve the building's energy performance, to install green roofs, to provide renewable energy production systems or for inhabitants' own leisure.

In order to generate practical and applied results, a vulnerable area in the city of Castellón (east Spain) was selected. The city's recent land-use plan defined this area as vulnerable [15–18], and it is characterized by a mixture of building typologies, most of which are old and obsolete. Thus, it could benefit highly by hypothetical intervention. A previous diagnosis of existent roofs should be made to analyze structural limitations, thermal properties and other aspects like orientation, possible uses, and so on.

Some benefits are observed. On one hand, roofs are an important part of the thermal envelope, which is totally exposed to outer conditions. Their refurbishment could contribute to improve buildings' energy performance and to reduce CO2 emissions. To this end, some representative buildings were selected, and the results were extrapolated to the neighborhood scale. On the other hand, using the space on some roofs could also contribute to increase green areas in the urban environment. Additionally, as roofs are currently underused [19], appropriate use and exploitation would contribute to sustainable cities and positively influence the social resilience of the city. Accordingly, some roofs could accommodate social functions, such as meeting places for residents.

The proposed solutions are meant to place in order the magnitude of benefits and other refurbishment solutions—even combinations of solutions—can be used. An actual intervention would require more accurate conditions to be observed in order to consider the legal framework, property regime issues and exact conditions of each building. A specific building is finally presented as an example to illustrate other options, where the combination of some proposed solutions could apply.

#### **2. Materials and Methods**

This work was undertaken in four main stages.

The first stage of the work involved data collection. First, a review was done on the regulations applied to build roofs and about constructive solutions at different times. Second, data on the selected area were collected. The chosen neighborhood is included as a regeneration and refurbishment area (ARRU, standing for Área de Regeneración y Renovación Urbana in Spanish) according to the recently developed land-use plan [12]. ARRU are vulnerable areas according to urban, residential, social and economic features and are meant to be prioritized to make urban regeneration interventions. Third, the data on the buildings in the area were collected using Cadastral Office information. This allowed us to identify buildings by their cadastral reference, and to address and provide information about plot area, built area, number of floors, number of dwellings and year of construction. Using the cadastral cartography and the Google Earth tool, roof types were identified and measured.

The second stage was meant to suggest refurbishment solutions for roofs. A cross-checking of roof types and refurbishment solutions was undertaken by considering parameters like load capacity, orientation, usable area, etc., to not dismiss any possible solution linked with a specific roof type and to select the optimum solution in every single case. A multicriteria analysis was used to assign applicable solutions to different roofs.

The third stage estimated the benefits for the area. Statistically representative buildings were selected to estimate quantifiable benefits. Improving buildings' energy performance by roof refurbishment was calculated with the CE3X energy certification software. This official software is approved by the Spanish Ecological Transition Energy Ministry [20–22], available at: https://energia.gob.es/desarrollo/EficienciaEnergetica/CertificacionEnergetica/DocumentosReconocidos/ Paginas/procedimientos-certificacion-proyecto-terminados.aspx (last accessed 5 June 2020). Those buildings that statistically represented the whole building stock were simulated. To simulate the average buildings, the data obtained from dynamic Tables in Excel (Supplementary Materials) were used, which allowed the selection of real buildings whose characteristics came close to average values. This implied that real orientations, measures for façades and windows, and so on, could be inputs in the software by assuming that outputs gave an approximate order of magnitude. The outcome of the simulation provided information on energy demand, energy consumption and carbon emission savings. Other environmental benefits, such as greener areas in the neighborhood, were also calculated. Some social benefits linked to the enjoyment of roofs by dwellers were also considered.

In the fourth stage, these data were extrapolated to the whole urban area so that the benefits of a potential intervention on the neighborhood scale could be estimated. Besides the neighborhood scale, a specific building was selected for simulations to, by way of example, implement a combination of some refurbishment solutions.

This paper is structured as follows: the background section briefly introduces the general goal of achieving sustainable cities and the role of buildings as relevant elements in complex urban ecosystems. Then the evolution and use of roofs in history, how they have become underused and underrated in buildings and how roofs can contribute to sustainability, are highlighted. Moreover, an analysis of the evolution of regulations on roofs construction was done to understand the different construction solutions for each period. Regulations on structural requirements during different periods were reviewed to analyze the technical applicability of the refurbishment solutions. Regulations on the thermal performance of buildings and their evolution in recent decades were also examined as this is a key factor to consider in sustainability terms. The next section explains the methodology and the steps undertaken in this work. Then the urban area selected as a case study is introduced. We present a brief description of the buildings, roof types according to their year of construction and their current use. Then an analysis of the different refurbishment solutions was carried out and they were linked with the physical possibilities of current roofs. The optimum solution to each roof type was selected by considering technical and environmental criteria. Finally, the achieved benefits were analyzed and estimated on the neighborhood scale. The accomplished improvement and the optimum roof-type solution combinations offered valuable information that could help the municipal administration in its decision-making to allocate funds for regenerating the area. Finally, an analysis of a specific building is presented below to illustrate the combination of different solutions.

#### **3. Results**

#### *3.1. Case Study*

#### 3.1.1. Urban Area

The urban area selected for this study is located in the city of Castellón de la Plana, a medium-sized Mediterranean coastal city located in east Spain, with about 170,000 inhabitants. According to the recent land-use plan, there are 17 vulnerable areas or neighborhoods in this city, called ARRU (standing for areas of regeneration, refurbishment and renewal). These areas are intended to be prioritized by the public administration to allocate funds in order to undertake regeneration and refurbishment [14,23]. Most of the neighborhoods in the city are located inland, about four kilometers from the sea coast, except for the neighborhood called Grao, which is stands by the sea, which especially distinguishes this area.

The Grao neighborhood was selected as the case study. This area corresponds to District 9 in the city and is formed by census Sections 09001, 9002, 9003, 9004, 9006, 09,007 and 9010. Together they form ARRU15 according to urban, building, socioeconomic and sociodemographic indicators [23]. All the vulnerability categories are present in census Sections 9002 and 9003. The worst vulnerability in buildings is present in 9001, 9002, 9003 and 9004, which coincide with a high-density urban area. The remaining area is formed mainly by single-family houses. In order to diagnose, propose solutions and quantify the benefit of refurbishing roofs, the area formed by census Sections 9001 to 9004 (presented in Figure 1) was selected.

**Figure 1.** Location of the selected urban area.

#### 3.1.2. Analysis of the Building Stock

In this study, buildings are grouped as typology and building period by considering two typologies, namely single-family house (SfH) and multi-family house (MfH), as suggested by Annex I, Section 5 of the EPBD for residential buildings. At the same time, they were structured according to five different

constructive periods having been adapted to both normative periods and cadastral information: 1840–1936, 1937–1959, 1960–1979, 1980–2006, 2007–2012.

The selected area is made up of 794 buildings, of which 775 are residential buildings according to Cadastral Office information, with 335 MfH and 440 SfH.

Data were arranged after contemplating the period when they were built. By considering the total building stock, only about 3% were post-CTE built, which confirms the energy rehabilitation need. As observed in Figure 2, the greatest building activity corresponded to periods 1960–1979 and 1980–2006. About 44% of MfH were built during 1960–1979, followed by 38% during 1980–2006. Almost 70% of SFH were built from 1980 to 2006. During this period, a significant increase took place during 2000–2005, when major developments during the real-estate boom in Spain were built, mostly terraced houses.

**Figure 2.** Number of residential building for year of construction and building typology.

#### 3.1.3. Roof Types

To complete the previous quantitative analysis, this section examined roof types. This variable is crucial to assign possible refurbishment solutions, where the original constructive solution needs to be known. Accordingly, two main roof groups were found in the area: sloped and flat. In turn, the latter was subdivided into non-walkable or walkable. Finally, in some cases, roofs are located in inner courtyards. For practical purposes and in relation to potential refurbishment interventions, we also differentiated between roofs for community or private use. Consequently, the roofs in the present study were classified as follows:

	- - Community walkable roof (CWR), with access to all dwellers. They are usually intended for different purposes, such as clothes lines, storage rooms, etc.
	- - Private walkable roofs (PWR) for personal use. They were not included in this study because they are terraces for private use.
	- -Private inner courtyards (PIC): often used by first-floor dwellers;
	- -Community inner courtyard (CIC).

To provide an initial idea of the variability and extension of these four main roof types, their area and location are plotted in Figure 3. Figure 4 quantifies this information.

**Figure 3.** Location of roof types in the area.

**Figure 4.** Number of roofs per building typology, roof type and period.

As seen in Figure 4, by considering the number of buildings, inner courtyards represent the highest percentage for period 1980–2006, followed by period 1960–1979 that represents 53% and 23%, respectively, for this type.

Figure 5 presents all the integrated information of the roofs in the neighborhood and considers the five building periods, the two building typologies (in columns) and the six roof types (in lines) that account for 60 groups. All the information is represented proportionally to the area in rectangles. walkable roof presents the highest percentage, 40%, followed by sloped roof, with 27% of the total area, inner courtyard with 23% of the area and non-walkable roof under 10%. Despite the large number of SfH, when considering the roof area almost 77% of this area corresponds to MfH, as we can see in Figure 5.

**Figure 5.** Roof areas per period, building typology and roof type.

The biggest area was found for the community walkable roof in MfH for the period 1960–1979 (1960–1979/MfH/CWR) combination, followed by the sloped roof in MfH for the period 1980–2006 (1980–2006/MfH/SR). When focusing on MfH, we found that they were built mostly during 1960–1979 and 1980–2006, with 45% and 60% of the area of their period, respectively. Regarding SfH, about 60% of the roof area corresponded to period 1980–2006, and the remaining 40% was distributed during the other periods. When considering each roof type, 72% of the area of sloped roof corresponded to period 1980–2006, 54% of the area of walkable roof was built during 1960–1979, most non-walkable roof also corresponded to periods 1960–1979 and 1980–2006, about 39% per period, and 65% of the area of inner courtyard were related to period 1980–2006, which coincides with the periods when building activity was more prominent.

#### *3.2. Refurbishment Solutions*

Roofs can benefit from being refurbished in many ways. Maintenance of buildings, energy savings, economic income and ecologic benefits can be obtained depending on the selected solution. However, as the solution must adapt to the specific conditions of the location and existing roof, not every solution would apply to each case.

Hence, depending on the starting conditions, different factors will determine the solution. Some limiting factors are to do with urban and architectonical issues. Sometimes there are legal limitations according to urban plans that determine the interventions to be made to roofs, linked with the allowed buildable area, number of floors, height, etc. Another crucial aspect must do with structural resistance and the loads the system can support, which must be checked. Moreover, the area, orientation and geometry of roofs are decisive for implementing certain solutions; for example, if there is enough room to install some facilities, if the orientation is appropriate for solar radiance gains or if there are solar obstacles to be considered, etc. Other factors are related to the economic cost of the intervention, such as the investment and maintenance cost of the solution.

The benefits obtained from the intervention should be observed in the decision-making process as they may add value to the building. For example, some solutions could improve a building's energy performance and reduce energy bills and carbon emissions from using the building which, therefore, makes the urban environment more sustainable. Other solutions may be beneficial for different reasons, such as their contribution to reinforce the social relations of dwellers, if they consider it convenient to take advantage of this underused space for community purposes.

In nonresidential buildings such as hotels, office buildings or commercial buildings, leisure uses, such as sports, restaurants, cafes, and so on, increasing the usable surface of some businesses is a possibility. Some large roofs can be employed for advertising to provide extra income to owners.

Considering the residential building stock, some refurbishment solutions are described in the following subsections.

#### 3.2.1. Green Roofs

Green roofs (GR) can cover a roof with vegetation either partially or completely. Therefore, it needs a growing medium placed on top of a waterproofing membrane and must also contain a root barrier layer and a drainage and irrigation system. The literature review shows that this entails many benefits, such as providing insulation, which improves the building's thermal performance by making energy savings [24–26] and could be achieved with the addition of thermal insulation. However, this solution entails other added benefits. It also combats noise pollution and can reduce noise annoyance by road traffic [27]. Other environmental benefits are linked with improved urban environment resilience, such as better rainwater absorption, more green areas in the urban environment, carbon sequestration, better air quality, lower urban air temperatures, mitigating the heat island effect, etc. [28–30]. It also contributes to create a habitat for wildlife, reduces people's stress by providing a more esthetically pleasing landscape [30,31] and contributes to solve the shortage of green spaces and land resources [32]. There are many varied technical solutions for installing green roofs. Some can be considered intensive systems and require thicker ground layers to support a wider variety of plants. However, they are heavier and require more maintenance. On the contrary, thickness of extensive roofs can range from 6 to 20 cm, are less maintenance-demanding and lighter than intensive solutions. Finally, some solutions exist in between, which are called semi-intensive [32–34]. Theoretically, this solution could be placed on any roof. However, on sloped roofs, inclination could complicate both installation and maintenance. Moreover, minimum solar radiation should be guaranteed for vegetation. Therefore, flat roofs with solar access seem, a priori, the most appropriated roof type for this solution.

#### 3.2.2. Solar Panels

According to Fuentes et al. [35], domestic hot water (DHW) accounts for about 20% of the total primary energy use by housing. A study by Pomianowski et al. [36] compared the energy use for DHW in some European countries and found that the final energy use percentage falls between 15 and 40%, and around 15% in Spain. The study by Gautama et al. [37] demonstrates the long-term economic feasibility of solar water heating systems, although the payback period depends on many factors like price of fossil fuels, solar insolation, etc. The implementation of solar panels (SP) will depend on the roof area and orientation, as well as on its location in the urban area. In the study area, the proper solar

orientation is southern or slightly southeastern [13]. Northern-oriented roofs would not be suitable for this solution or these roofs are surrounded by solar obstacles like taller buildings. The installation of solar panels to contribute to DHW demands can be a suitable solution in the study area, especially for SR for which other options are not considered. They can also be seen as a good solution for some flat roofs, such as non-walkable roofs or small walkable roofs, where other options are inadequate. Installation on sloped roofs is slightly cheaper because they do not need a substructure to support panels. solar panels would increase the renewable energy supply in the neighborhood and reduce energy use and, therefore, energy bills.

Photovoltaic panels are also very interesting—especially in locations where solar radiance is high [38]. Other authors have demonstrated the profitability of this solution in non residential buildings [39,40]. Even the combination of solar panels with green roofs can be found in the study of Berto et al. [41]. They produce energy that is an interesting alternative to achieve economic and environmental benefits. Unfortunately, however, this solution is not completely standardized in Spain for residential building, probably due to the solar energy tax established by Royal Decree 900/2015. Later this law was derogated by Royal Decree 15/2018. As a result, the system has been rarely used—especially in MfH. Nevertheless, it undeniably offers a high potential in the near future and is, in fact, currently being promoted by the government [42].

#### 3.2.3. Residents' Association Meeting Area

The available area misused on walkable roofs can be used for many purposes, such as meetings, social encounters, installation of urban orchards (included in green roofs), solariums or other uses to promote the social interaction of dwellers [31,43,44]. Considering the legal and structural limitations, a residents' association meeting area (RA) could be placed. This could feature various possibilities, from light pergolas to heavier constructions—depending on the starting conditions. Load, complexity and cost will vary depending on the selected solution.

#### 3.2.4. Adding a New Floor on the Existent Building

If this option is allowed by the urban plan—and the structural capacity permits it—adding a new floor (NF) would add a noteworthy economic benefit to ownership.

#### 3.2.5. Selecting the Proposed Solutions

For this work, the new floor solution was rejected because it is a very limited solution that can be applied in a few cases due to urban plan limitations and, moreover, because structural capacity should be enough to support the loads of the added floor. Photovoltaic solar panels were not considered due to lack of experience to date in residential buildings, but they are an interesting and very convenient proposal to be analyzed in the near future as they can imply potential economic profit and energy savings. Therefore, the green roof, solar panels for DHW and residents' area solutions were considered for the scope of this work. Regarding green roofs, an extensive solution was selected over the intensive or semi-intensive options because of the lightest structural requirements and the lowest economic investment and maintenance [31,33,45]. Regarding the solar-panel solution, it is considered to be most appropriate for the neighborhood as it receives high solar radiation most of the year. Castellon is classified solar zone IV in the Spanish territory, with an scale from I to V from the lowest to highest radiation, (according to DA DB–HE/1, document complementing the HE document), which means high mean annual global solar radiation (4.6–5 kWh/m2). Moreover, this solution supports norm CTE, Section HE4, which requires a minimum contribution of renewable energy to cover the DHW demand, which is 60–70% in the study area. As regards residents' area, we selected a multipurpose light wooden pergola solution to minimize both load and cost. This solution could provide an area where neighbors can gather for their meetings and other agreed uses according to dwellers' interests.

Table 1 summarizes the selection for the undertaken analysis:

#### **Table 1.** Selection of refurbishment solutions.

#### *3.3. Type of Roofs Vs. Refurbishment Solution*

The descriptive cadastral data were analyzed using the dynamic Tables in Excel. Some aspects were completed with the available cartography (Spanish Cadastral Virtual Platform) to verify certain aspects, such as orientation or inner courtyards and to identify the private uses to be ruled out for the study.

The applicability of the refurbishment solution to roofs was done by a multicriteria matrix, where all the analyzed information of roofs was crossed with the technical possibilities of the selected solutions (see Supplementary Materials). Of all these premises, some starting hypotheses were put forward:

After assuming all these hypotheses, five combinations of refurbishment solutions/roof types appeared (see Supplementary Materials):

#### *3.4. Estimating the Benefits of Refurbishment*

A statistical analysis of typologies provided us with the average values for number of floors, number of dwellings, usable area, roof area and energy requirements for DHW (based on Regulation CTE-DB-HS4) to obtain representative buildings for energy performance simulations. By doing so, the results of energy savings and carbon emission reductions due to the refurbishment could be extrapolated to the neighborhood scale to obtain an order of magnitude of the potential improvement to the whole area. The area is mainly made up of MfH, of 6–7 floor buildings, with 20–30 dwellings ranging from 1440 to 2968 m<sup>2</sup> of usable area and 2016–3427.20 L/day requirements for DHW. The average SfH building has three floors, 168 m<sup>2</sup> and 112 L/day requirement for DHW.

Energy demand will lower in those scenarios that consider the GR solution because roofs form part of the thermal envelope. This must do with the solution's higher thermal resistance (1.969 m2K/W) and, consequently, the lowest thermal transmittance (0.508 W/m2K), which would improve energy performance. Figure 6 shows the composition of the selected extensive solution and the detail of its thermal properties [48].

**Figure 6.** Green roofs (GR) extensive solution. Composition and thermal properties (\* according to CTE-DB-HE1).

Considering that the residents' area solution does not influence the building's energy performance, and that the thermal resistance value does not vary from community walkable roof to non-walkable roof during the same period, the simulation cases amount to five buildings, represented by Period/Building Typology/Roof Type:

Table 2 presents the five combinations, the main features of the representative building (average values for number of floors, dwelling units, usable area, roof area and DHW requirements) for simulation purposes and the total roof area of each combination in the neighborhood.

Depending on the combination, the achieved benefit can be estimated. Some environmental benefits are obtained with the green roof and solar-panel solution as they improve the building's energy performance. The energy demand (kWh/m2.year), final energy consumption (kWh/m2.year) and carbon emission (kg CO2/m2.year) reductions can be estimated by the energy performance simulation software CE3X. Moreover, green areas in the neighborhood increase by 8530.70 m2 (Table 1). Although the Residents Area solution cannot be valued in terms of environmental or economic benefits, it entails social advantages that contribute to the sustainability of the urban area.

Table 2 summarizes the benefits obtained by simulating the refurbishment scenarios using CE3X. Table 2 indicates that energy demand lowers when green roof is implemented as the thermal transmittance of roof decreases (Figure 7); second, energy use savings are made in the green roof and solar-panel solution scenarios, together with lower carbon emissions. All the software outputs are calculated per square meter and then extrapolated to the neighborhood scale by considering the potential improvement accomplished for the total roof area in the neighborhood.

**Figure 7.** Specific building and refurbishment rendered.

As observed in Table 2, a solar panel for DHW provides greater energy use reductions than green roof. Implementing a solar panel leads to a 10% reduction in SfH, and values rise to around 30% for MfH. Regarding the green roof solution, studies suggest reducing buildings' energy consumption by up to 5% [37]. The results obtained with the case study via simulation ranged from 1.7% to 3.2%, which are similar to those given carbon emissions. Energy demand also reduces with green roof due to lower roof thermal transmittance. All the obtained reductions are worth considering when the results are extrapolated to the neighborhood scale, with savings of 40,782.85 kWh/year in energy demand, 579,595.70 kWh/year in energy consumption and 148,364.94 kg CO2/year in carbon emissions.

**2.**Scenario features of representative buildings and total savings in the area.

**Table**

The calculations suggest an interesting benefit regarding energy savings and carbon emissions, along with other environmental and social advantages, such as the increase in green areas in the urban environment, 8530.70 m<sup>2</sup> in non-walkable roof and 37,248.98 m2 in community walkable roofs.

As mentioned earlier, it is an order of magnitude and the particular conditions of each building should be observed to obtain more accurate results. Scenarios may vary to accomplish the optimum solution. A combination of the proposed solutions can even be suggested in buildings where different roof types coexist. By way of example, a building where community walkable roof, non-walkable roof and sloped roof are present and all the analyzed solutions can be implemented, was selected. Knowing the exact building features can offer a more accurate scenario of the refurbishment.

Table 3 presents the main building features and summarizes the benefits obtained from the refurbishment proposal, which is completed by the estimation of the intervention's economic cost. It is an MfH building formed by six dwellings, two commercial premises and 10 parking lots. It was built in 1994 in accordance with both Regulation NBE-AE-88 on structural requirements and Regulation NBE-CT-79 on thermal requirements. The building combines three roof types: non-walkable roof over the staircase, community walkable roof and sloped roof facing southeast, with 25, 108.50 and 134.64 m2, respectively. After checking the structural capacity with NBE-AE-88, which came into force in 1994, the following solutions are proposed: green roof suggested for non-walkable roof, as shown in Figure 7; the resident's area is suggested for community walkable roof by estimating a wooden pergola of 60 m2. Finally, solar panels for DHW are proposed for sloped roof with the proper orientation. The load resulting from the solution and the improved transmittance value in green roof are also presented in Table 3. The cost of the intervention was estimated from the construction prices database (CYPE) [49], with a total amount of 18,142.45€ (2267.80 €/owner, 6 dwellings + two commercial premises, not including professional fees, licenses and taxes). The combination of these roof refurbishment solutions provides economic and social benefits that are all relevant in sustainability terms.

**Table 3.** Description of the specific building.

\* Prices: RA—60 m<sup>2</sup> wooden pergola, unit price—60.98 €/m2; GR—25 m2, unit price 96.95 €/m2; SP—8 panels, unit price 1507.80 €/panel.

The economic analysis of the viability of the global cost (investment, running and disposal costs and the entailed energy savings), according to the comparative methodology framework for calculating cost-optimal levels of minimum energy performance requirements for buildings and building elements (Commission Delegated Regulation (EU) No 244/2012 of 16 January 2012, supplementing Directive 2010/31/EU of the European Parliament and of the Council on the energy performance of buildings), is not very optimistic. Even when considering the macroeconomic perspective of the methodology that assigns a price for carbon emissions (public cost) that would be included as savings when energy performance improves, the payback is too long, over 30 years. So, the proposed solution is not very appealing from the economic perspective. However, that term could be shortened if some funds were allocated to the intervention (up to 40% of the cost of the investment and up to 75% for low incomes, according to Order 1/2019, 18 February, of the Regional Administration in Charge of Housing, Conselleria de Vivienda, Obras Públicas y Vertebración del Territorio, which approves funds for ARRU for the National Housing Plan 2018–2021) (see Supplementary Materials). Moreover, there are other gains that would be obtained from the activation of the refurbishment economic sector, e.g., from the generated taxes (VAT, licenses, etc.), together with increased property value due to the intervention. Then there other costs that should be included in the balance of payments in sustainability terms, namely public costs, which means that they are difficult externalities to monetize. Those could be the benefits linked with an increase in green areas in the neighborhood or social benefits associated with the use of wasted space.

Other solutions that were ruled out in the proposal of this work could also be considered. For example, the use of photovoltaic panels could be supported by considering the economic profitability of the investment. A basic simulation was performed for this specific building using the European Commission's simulation tool, Photovoltaic geographical information system (available at https://re.jrc.ec.europa.eu/pvg\_tools/es/#TMY, last accessed 12 August 2020). According to the obtained results, installing 25 PV panels on the sloped roof would save 13,232.61 kWh/year. This facility would increase the energy and carbon emission savings significantly compared to the 2422.17 kW/year obtained with DHW panels. The global cost economic approach shows that, when DHW solar panels are replaced with PV panels, the payback period shortens substantially, with positive values for the net present value and the investment return is even obtained in about five years in the funded scenario (see Annex A, tabs 10 to 13).

#### **4. Discussion and Conclusions**

Current urban areas are complex environments that include most of the population and need varied and combined solutions to enhance sustainability. Buildings' improved energy performance has become a crucial target in recent years to seek low carbon economies. Moreover, today's roofs are underused and have been devalued compared to their use of old. From this viewpoint, roofs can be seen as an opportunity because they form part of the thermal envelope and can contribute to improve buildings' energy performance—especially old and obsolete buildings where energy refurbishment and updates are necessary. Besides the environmental benefits, some roof refurbishment solutions offer many other advantages that can be hard to monetize but are extremely interesting in sustainability terms by contributing to ameliorate citizens' lives as social benefits.

This work analyzed the improvement potential of consolidated urban environments through roof refurbishments. It focuses exclusively on roofs to analyze the possibilities linked with an underused part of the building. One of the achieved benefits is the building's energy performance improvement, which is especially needed in vulnerable dwellings that usually present very poor thermal performance. In this regard, the roof's contribution is partial and integral energy refurbishment of housing would be advisable to achieve optimal results. Some suggested solutions allowed savings to be estimated in terms of energy and carbon emissions and other more social-oriented benefits. To consider the neighborhood scale, an area was selected, and a thorough analysis of the building stock was performed. The existent constructive solutions of roofs were analyzed with the georeferenced information from

the Cadastral Office of the actual buildings. The actual constructive solution is crucial for suggesting adequate refurbishment solutions in practical applicability terms (load capacity, orientation, geometry, surrounding conditions, etc.). refurbishment solutions were assigned depending on the roofing system. To estimate some figures, the study focused on a specific vulnerable residential area in the Grao neighborhood in the Spanish city of Castellón, defined as ARRU in the Urban Plan. Three simple solutions were selected as being most likely implemented, although some others could also be included. Based on these assumptions, the study obtained savings of 119,123.35 kWh/year in energy demand, 666,007.43 kWh/year in energy consumption and 189,061.36 kg CO2/year in carbon emissions. In addition, 35,779.58 m2 of new green area were added to the area. The suggested solutions include other social benefits linked to the use, enjoyment and advantage of some wasted spaces in the urban area. However, we must bear in mind that the study provides an order of magnitude based on representative buildings, and a more accurate calculation would require an individual analysis of the parameters in every single building. This is illustrated by the example performed in the selected building, which combined three roof refurbishment solutions. Considering the economic analysis of the intervention, and based on the global cost calculation, it shows that the payback period is too long, and the investment is not profitable. However, the term could be shortened if some funds were allocated to the intervention when the area is considered to be ARRU. Moreover, in sustainability terms, other costs should be placed in the balance of payments when considering public costs, such as those linked with the increase in green areas in the neighborhood or those connected to the social benefits associated with the use of wasted space.

This work is based on a simplified and fixed theoretical scenario to gain a potential quantifiable amount of energy savings, an increase in green areas and carbon reduction and other non quantifiable benefits linked with the non economic factors that affect urban sustainability. A myriad of scenarios can occur under today's conditions and this is the main limitation of our analysis. In real applicability terms, the legal framework, property regime, etc., should also be observed as actual conditions because they are too complex, and an accurate estimation is unattainable. Further research is needed to explore different solutions and scenarios. Rooftop architecture could become an interesting solution for the energy retrofit of the entire building and could represent an important economic opportunity in multifamily buildings whenever applicable. Real projects with different solutions can also shed some light on current results. The influence of the photovoltaic energy option should be further studied because it potentially provides renewable energy for a real NZEB scenario. The development and standardization of this technology in residential buildings could be a means to achieve higher energy savings and to improve the economic viability of refurbishment. Hence further research should be conducted to seek new market strategies—especially in MfH—where a community meter could be installed in the building [46]. However, the results found in this study could be useful for decision-making to allocate funds for urban regeneration interventions, especially in vulnerable areas that usually present an old and obsolete building stock.

Although a previous analysis of the characterization of buildings, roof types and boundary conditions in the area is necessary, this estimation method can be replicated in other case studies.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2071-1050/12/19/8111/s1, Excel file.

**Author Contributions:** Conceptualization, M.J.R.; Formal analysis, M.J.R. and L.R.; Investigation, Á.P. and I.A.; Supervision, L.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** The APC was funded by the Department of Mechanical Engineering and Construction of the University of Jaume I, Castellón, Spain.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Article* **An Approach to Environmental Criteria in Public Procurement for the Renovation of Buildings in Spain**

#### **Teresa Soto 1, Teresa Escrig 1, Begoña Serrano-Lanzarote 2,\* and Núria Matarredona Desantes 2,3**

Received: 31 July 2020; Accepted: 10 September 2020; Published: 15 September 2020

**Abstract:** In order to contribute to climate neutrality within the EU in 2050, it is necessary for administrations to play a driving role through green public procurement for building renovation (GPPBR). Among the main barriers that slow down the GPPBR, a lack of knowledge of the parties involved can be highlighted. Faced with this scenario, the aim of this article is to provide a compilation, as a preliminary state of the art, of the most important environmental measures to bring to the GPPBR specifications. The methodology used for this compilation and critical analysis consisted of a systematic search for laws, regulations and guides prepared by Spanish public administrations, as well as looking into other international information sources, mainly collected from the EU. Despite the fact that related technical information is abundant, it is scattered and at times impractical. This study can be useful as a basis for both drafting specifications and highlighting the need to develop other specific and advanced technical procedures to assist GPPBR professionals.

**Keywords:** environmental; green public procurement; renovation; construction; energy; circular economy; innovation; green; sustainable

#### **1. Introduction**

There is a clear opportunity to promote building renovation through Green Public Procurement (GPP). The implementation of environmental measures in buildings for energy efficiency and transition to a circular model depends on the active involvement of all the agents around. Although the Public Administration, by function and regulatory work should first take these measures and play a leading role in the private sector.

#### *1.1. Green Public Procurement for Building Renovation (GPPBR) in the EU*

The main policies in the European Union are framed in the current climate and environmental emergency [1]. It is essential to achieve climate neutrality for the EU by 2050, and meet environmental goals committed by governments through the Climate Agreement: likewise, constructing play a relevant role, among other sectors such as transport.

On the one hand, it is imperative to reduce energy consumption caused by buildings themselves [2], since this sector represents around 40% of total consumption in the world [3,4]. Furthermore, 75% of all the buildings in the EU are energy inefficient, whereas their annual renovation rate is only 0.4–1.2% [4,5]. According to the European Green Deal [5], in order to achieve the EU goals, the intervention rate on buildings should at least double. Directive 2012/27/EU [6] requires that new buildings have nearly zero energy consumption and sets an annual renovation of 3% of the total area of buildings when it comes to central administrations, so that they meet current energy efficiency requirements. According to Directive 2010/31/EU [7], every Member State should set a long-term strategy to support the renovation of the building stock.

On the other hand, it is urgent to implement decisively the principles of a circular economy in buildings [3]. Awareness and knowledge on the characteristics of circular public procurement, based on the implementation of circular policies and strategies, are essential [8]. According to the New Action Plan for the circular economy in the EU [3], the building sector demands huge amounts of resources, uses around 50% of all extracted materials and generates more than 35% of the total waste. Directive 2008/98/EC [9] provides that Member States shall take action to prevent waste generation, by promoting reuse, repair and recycling of construction and demolition materials and products, among others.

Within this context, public procurement is a key action for implementing the EU environmental policies, since it makes up around 19% of the gross domestic product [10]. Thus, an effective green public procurement is needed, as a force for change. Directive 2014/24/EU [11] already introduces environmental considerations regarding award criteria, technical specifications and construction conditions. The EU also offers Member States an optional tool, the GPP criteria, as a reference for developing environmental clauses [12]. Despite the fact that these criteria offer great potential to carry out environmental policies, based on studies from an international background, it is found that the level of implementation of the GPP is varied, and it is generally limited [8,13–15]. The lack of knowledge and definition when it comes to introducing environmental criteria in tender papers, and the absence of practical information for designing, are some potential causes. Moreover, further development of the GPP criteria in relation to innovative solutions is required [15,16].

#### *1.2. Green Public Procurement in Building Renovation (GPPBR) in Spain*

In Spain, the regulation of the GPPBR starts from the environmental policies of the EU [17], as well as energy renovation needs of the existing building stock.

Around 21% of existing buildings in Spain are older than 50 years, and 55% were built before 1980, when there was no obligation to be thermally insulated [18]. Residential buildings are the highest consumers of final energy consumption caused by construction. However, buildings in tertiary sector, which occupy only 13% of total square meters of building space, consume 42% of final energy [19]. That is why these buildings and particularly those for Public Administration (such as health care, education, assistance, administrative centers...) show a very significant potential to reduce carbon footprint and other environmental impacts. In this respect, and given its exemplary role, Public Administrations establish specific obligations for building renovation in energy matters and concerning a transition to a circular economy model. The renovation of buildings themselves is part of this model, since one of the principles is to keep products and materials in use [20]. According to the National Action Plan for Energy Efficiency [21], the Central Administration should annually renew 3% of the total area of buildings—a goal nearly achieved in Spain during the period 2014–2019 [19].

It is estimated that public procurement in Spain represents between 10 and 20% of GDP, depending on the year [22]. As it is a key economic sector, public procurement in terms of building should include environmental criteria, which are collected in various regulatory tools. Among the provisions of the General State Administration affecting the GPPBR, it is worth mentioning the following:

renovation over 3% of the built-up area in public buildings of the General State Administration, and at least 3% of the buildings of regional and local administrations.

This state framework is as a reference for the different regional Public Administrations.

Regarding public procurement in Spain, the percentage of contracts in which the best quality-price ratio is valued as an award criterion is high if related to the EU average [30]. However, the implementation of environmental policies in the public procurement of buildings in Spain is low if compared to other countries. The group of countries known as "Green 7" (Austria, Denmark, Finland, Germany, the United Kingdom, the Netherlands and Sweden) [31] shows a higher number of tenders in terms of ecological criteria, rather than the rest of the EU countries. It also reaches the highest qualifications in questionnaires about environmental measures. One of these measures is the introduction of environmental management systems as well as the use of innovative tools for public procurement, such as the one related to life cycle [13,31]. Likewise, the Nordic countries, through their 2010 Action Plan, are pioneers in promoting sustainable production and eco-innovation [14].

However, in all EU countries, there is still a long way to go. An example is the lesser importance of environmental measures in the GPP, approximately 10% in the European context [14], if compared to other criteria. These can be costs, construction process report and delivery time. In some cases, the weighing of environmental criteria is even negligible. Especially in lower budget tenders, it can be seen that the financial approach tends to a higher valuation with regard to other criteria, such as the environment-related ones [31]. Likewise, the lack of adoption of the LCC criterion is generally observed [32].

There are several reasons why innovative or environmentally responsible public procurement are not yet fully implemented. The main barriers found are the lack of resources, knowledge, staff training, motivation and funding [8,31,33,34]. This has been confirmed in various studies about the implementation of GPP policies [30,31], and reflected in the Report on public procurement in Spain - 2017, prepared by the Ministry of Finance and Public Function [35]. Thus, the mentioned barriers have increased in small towns with fewer resources to set up specialized contracting departments. Without them, it is not possible to gain knowledge and obtain developed strategies for GPP [31]. As a consequence, the implementation of circular economy principles is often the result of random chance or unsystematic experimental models [8].

For this reason, it is necessary to develop suitable technical procedures for the award of contracts [35]. The dissemination of these procedures and the training of professionals who have to put them into practice, together with coordination and cross-cutting strategies of organizations are required, since the model design-tender-build in sustainable buildings requires minimal training and management to be adopted [36].

#### *1.3. Objective of the Article*

On this basis, the aim of this article is to open up new avenues so as to improve implementation of environmental criteria in the GPPBR in Spain. Among the main barriers, the lack of knowledge of the agents involved can be mentioned.

As a first step to facilitate knowledge, a compilation is made in Section 3, as a preliminary state of the art about environmental measures included in the regulations and guides of all Spanish regions, in line with the European context for implementation of GPP. In Section 4, an analysis is carried out concerning the feasibility of applying such measures, alongside the identification of potential barriers. Section 5 contains the review of measures along with conclusions, limitations and possible future research. Given the abundant but scattered information, there is a need to develop advanced technical procedures for professionals responsible for public procurement, including evaluating indicators.

All of this seeks to move towards an objective: the GPPBR should be truly "ecological". Thus, the Administration should have an exemplary role. Knowledge generated should help increase the motivation among professionals and evaluate proposals, not just according to initial costs but the best value for money. This would allow to gain the benefits of sustainable renovation throughout the life cycle and promote climate neutrality of the EU in 2050.

#### **2. Methodology**

As explained above, the purpose of this article is to contribute to the improvement of knowledge so as to carry out the GPPBR in Spain. That is why methodology used is based on an approach on the state of the art of the major environmental measures proposed by the Spanish Public Administrations, regarding the goals set by the EU about building renovation. Due to the particular features of each region and the territorial organization in Spain, these measures were set out by the State and regional administrations through various papers: laws, regulations and guides. Each of them within the scope of its competencies. The present article is an in-depth study of the regional GPPRB.

The methodology used is summarized in Figure 1 and described below.

In order to obtain documentation about the GPPBR at regional level, internet sites of all Spanish regions and Autonomous Cities were checked first. All of them can be accessed through the "General Access Point" web site, created by the General State Administration:

#### https://administracion.gob.es/pag\_Home/atencionCiudadana/SedesElectronicas-y-Webs-Publicas/websPublicas/WP\_CCAA.html#.Xzu2Pugza00

Next, by entering each site, a search on subjects about sustainability in construction and GPP was carried out: building, renovation, climate change, energy efficiency, circular economy, waste management, public procurement of innovative solutions (PPI), environment, territory, sustainability, and urban planning. This search led to different web sites of regional governments: departments, councils and organizations for energy, business competitiveness, building, housing, land, etc. General and specific tools were found about the implementation of measures in the GPP and building renovation. Appendix A contains a broad list of laws (L), regulations (R) and guides (G) found (a total amount of 145 papers). Figures 2 and 3 provide a summary of the main topics and the percentage that each type of tool represents over the total analyzed. Figures 4 and 5 show the main topics related to the documents found.

**Figure 1.** Methodology.

**Figure 2.** Documents considered for the compilation of environmental measures in the green public procurement for building renovation (GPPBR) of the Spanish regions and Autonomous Cities.

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**Figure 3.** Percentage of papers collected according to the type of document.

**Figure 4.** Number of laws, regulations and guides compiled according to topics.

**Figure 5.** Percentage of documents collected according to topics.

Once papers were collected, they were analyzed to draw environmental measures specifically applicable to the GPPBR.

The environmental measures are set out in Section 3 together with a list of documentation as close as possible to the different subjects, or documentation developing advanced and useful aspects to bring into contracting procedures. Although various laws, regulations and guides were compiled from all regions and autonomous cities, the list of these papers as well as measures included in this article is not exhaustive. Yet, it is enough to obtain consistent results as a reference, and open up avenues for further research. Moreover, it is necessary to mention that a comparative study among regional Administrations is not the purpose of this approach.

At the same time, other international sources on implementing environmental measures in buildings and GPP were analyzed. Particularly, legal framework and criteria for the EU GPP, as well as other articles and papers outlined in this article, were taken as a basis. The study of all documentation allowed a rough idea of the situation and issues of the GPPBR, as explained in Section 1. All of this made it possible to enrich the analysis, discussion and conclusions of the measures collected within a broader context, as Sections 4 and 5 show.

#### **3. Results. How is GPP Implemented in Spain?**

#### *3.1. Regional Administration Papers*

Based on the state regulatory framework set out in the Introduction, regional Administrations have drawn up a large number of laws, regulations and guides related to the subject of this article. The following are papers concerning climate change, energy transition and circular economy, closely related to the GPPRB.

Although the GPP model specifications are very helpful for contracting authorities, there are few that have been prepared. These include the following:

In recent years, since the approval of Directive 2014/24/EU, of which the LPSC [23] is transposed, many guides related to GPP have been elaborated, even if these papers address the subject broadly, and also include building-related aspects. Among them, it is worth mentioning the following:

It should be noted that some regions collaborate with international projects to develop technical measures and evaluation criteria within the GPP. A remarkable example is the Basic Guidelines for applicating environmental criteria in the purchase of products/services by public administration of the GreenS project [66]. The Regional Energy Agency of Cádiz and the Andalucía Federation of Municipalities and Provinces have taken part in it.

Some guidelines were found, containing environmental criteria for buildings. Due to the relevance for adding environmental measures to the GPPRB, the following should be mentioned:

enhance public procurement in building, considering environmental impact during the life cycle, with good practice examples. Although the content focuses on office buildings, recommendations are applicable to buildings with different uses.

It should also be noted that the guidelines set out in this section are not mandatory, so the application of environmental criteria proposed for the GPPRB is left to contracting bodies.

However, mandatory application of laws and regulations is bringing about results. Specific actions result from compliance with regional energy efficiency plans for buildings and public facilities. For example, in Catalunya, nearly all the energy acquired by the regional Administration is certified as 100% renewable [72]. In the Comunidad de Madrid, heating renovation and air conditioning installations in public buildings represented 64% of actions of the regional plan during the first year [73]. In the Comunitat Valenciana, it was possible to reduce energy consumption in public buildings by 11 million kilowatt hours in one year [74].

Results after putting into practice regional circular economy strategies are also observed. For example, in Extremadura, advice at the local level to identify municipal green initiatives is being given, as those related to carbon sinks [75]. In Galicia, the first public building built entirely using certified native wood has been put out to tender, within the framework of the Lugo Biodinamic project [76]. In the País Vasco, the evolution of CDW recycling in recent years is upward (42% in 2013, 59% in 2015 and 61% in 2016), but there is still room for improvement until reaching 70% set as a target for 2020 [77].

Finally, it is interesting to mention that several regional administrations carry out annual monitoring of the GPP results. For example, in the País Vasco, 24% of ecological tenders were carried out in 2019, which represented 22% of the total economic amount. In the building sector, the GPP represented 27%, with an economic volume of 28% with respect to the total tendered in that sector [78].

#### *3.2. Environmental Measures*

In this section, the most relevant measures set by Spanish regional Administrations are compiled and grouped according to the following subjects: passive energy saving measures, proactive measures for energy efficiency and water saving, life cycle, products and waste management. Those measures required by administrations as an example to be incorporated into the GPPRB, are presented next. Figure 6 shows the number of measures in each subject.

3.2.1. Passive Measures for Energy Saving and Environment Protection

Passive strategies should be adopted from the beginning of the architectural design phase:

So as to reduce energy demand, it is essential to act on the thermal envelope:

To obtain heat gains, solar capture solutions can be added: glazed galleries, Trombe walls, thermal inertia walls, etc. [67–69,79,80].

With regard to sun protection, the following recommendations are provided:

It is advisable to provide natural ventilation through building design. For this purpose, choosing the best location on the plot should be a factor to consider; the most suitable shape, size and orientation of the building and its openings; the provision, if necessary, of screens (natural or artificial); interior layout; the shape of the cover, etc. Concerning solar protection, the following types of ventilation can be adopted:

To provide the building with cooling, natural air cooling is recommended: by introducing treated air to lower temperature or increase humidity content. Depending on site conditions, different types of air treatment are proposed:

The incorporation of natural habitats in the vicinity of buildings or in the interior, such as gardens, groves or patios with vegetation, contribute to all kinds of benefits; the design and selection of plants and materials should be consistent with the intended purpose and friendly to the environment [67,69].

Bringing in space for bicycle storage and personal mobility vehicles (such as scooters and others) helps promote use and reduce carbon emissions, with better air quality [37,67].

Some examples obtained from the analysis performed are shown in Figure 7.

**Figure 7.** Examples of passive measures for energy saving proposed by Spanish regional administrations.

#### 3.2.2. Proactive Measures for Energy Saving

It is advisable to limit energy consumption in public buildings, with specific goals:

Promoting self-consumption can be achieved by incorporating renewable energies:

So as to set objectives including renewable energies, as the following cases:

Various administrations are acquiring electric power 100% from a renewable origin:

In order to upgrade the energy efficiency of interior lighting installation, the following recommendations should be adopted: replacing luminaires with LED lighting systems, using control systems, regulating the level of lighting according to natural light, as well as sectorize circuits [67,68,70,81,84].

In terms of energy efficiency, it is also advisable to incorporate energy-efficient sanitary taps [67]. To promote a greater use of electric vehicles, some Administrations are planning a major endowment of charging points than established in the Electrotechnical Regulation for Low Voltage (ERLV) [86]. An example is the Generalitat Valenciana, through the Green Guide [67], and the Generalitat de Catalunya, which contemplates the installation of 200 charging points in Administration buildings [41,87].

Itis also advisable to contract energy through a central public procurement service of Administration [30]. The Junta de Castilla y León created the OPTE Platform to facilitate the energy purchase of different Board bodies and energy contracts optimized annually [84].

Other measures related to energy saving are: performing reactive energy correction, applying inmotics with IT tools for monitoring consumption, proposing regular studies of tariff optimization or an analysis and adaptation of contracted power, as well as training users in good energy practice.

Figure 8 shows some examples of proactive energy efficiency policies obtained from the analysis.

**Figure 8.** Examples of proactive measures for energy saving proposed by Spanish regional public administrations.

#### 3.2.3. Proactive Measures for Water Saving

Some of the measures proposed are the following:

• Installation of: consumption reduction devices and systems for reuse gray water and/or rainwater [67,69,88], specifying maximum flow rate in taps and maximum flush volume in toilets and urinals, as well as saving devices [67,88,89]; treatment of waste water, efficient irrigation systems even with recycled water [67]; components for saving water such as flow restrictors, the overflow of rainwater collection system with discharge to surrounding surface waters or underground; sustainable urban drainage systems (SUDS) to collect rainwater [70].

Some examples of these measures obtained from the analysis are summarized in Figure 9.

**Figure 9.** Examples of proactive measures for water saving by Spanish regional public administrations.

#### 3.2.4. Life Cycle

The advisable measures regarding a building's life cycle, which are, therefore, more ambitious, are the following:

**Figure 10.** Examples of life cycle measures proposed by Spanish regional public administrations.

#### 3.2.5. Products (Measures Related to Circular Economy)

In general, many measures were found on specific products following a circular economy model:

percentage according to the weight of recycled material in products. This guide also recommends using concrete with recycled aggregate, and includes an annex with the approximate proportion of recycled material in particular products, as well as a list of building elements and recycled materials. In this area, the Sustainable Building and Renovation Guide of the País Vasco [70] suggests that at least 25%, by weight, of raw material has recycled origin.

Some examples of product measurements obtained from the analysis are shown in Figure 11.

**Figure 11.** Examples of product measurement proposed by Spanish regional public administrations.

#### 3.2.6. Waste Management Measures

A proper management of CDW is essential for a transition to circular models in the building sector. The recommendations found in this area are:

Figure 12 shows some examples of waste-management measures obtained from the analysis.

**Figure 12.** Examples of construction and demolition waste (CDW) management measures proposed by Spanish regional public administrations.

3.2.7. Environmental Assessment and Monitoring Measures

In this area, some recommendations found are the following:

#### *3.3. Application of Environmental Measures in the GPPRB: Examples*

As mentioned above, the tenders incorporating environmental measures with relevance in award criteria are still insufficient [14]. However, both in the EU and Spain, there are many success cases in which these measures are defined and valued. Below, three examples of good practice in Spanish regions are described:

In the three examples, the valuation of environmental measures on other criteria was much higher than 10% of the current EU average, as mentioned in the introduction.

#### **4. Discussions**

From the analysis of the source information on energy efficiency and circular economy in the GPPBR within Spanish regions, a series of questions arise about barriers to application and opportunities for improvement.

#### *4.1. Are All the Measures Feasible? Is the Sector Well-Prepared?*

In the measures analyzed themselves, barriers to application of different kinds are observed.

In the case of passive energy efficiency measures, there might be difficulty in implementing them in building renovation. Notably, bringing in thermal insulation or solar shadings in facades as well as renewable energy facilities on roofs may be restricted by municipal regulations. Therefore, local regulations should be modified, based on higher ranking guidelines and standards. For example, the Decree-Law 16/2019 [111] of Catalunya provides the placement of facilities for solar energy on roofs of existing buildings. For that purpose, specific terms were imposed, with no limitation of urban plan requirements.

Regarding renewable energies, there is controversy over the technical solvency criterion referring to the fact that electric power trading companies have the A label issued by the CNMC. This requires the electricity marketed to be of 100% renewable origin [112]. On the other hand, in order to make energy 100% renewable by 2050, not only the technology and price reduction are needed, but also political will. Regarding decarbonization in the Spanish building sector, it is essential to increase the level of electrification in energy demand, and prioritize renovation.

It is found that there are not very many measures related to the life cycle analyses, although these are vital to optimize results [3,4]. Furthermore, carrying out the LCC requires experience and competence. However, the sector appears not to have fully matured [69].

In relation to gray water reuse systems, these demand the installation of a treatment tank. Therefore, the practical application of this measure can be conditioned by available space [70].

Additionally, barriers caused by shortcomings in the construction product market itself are detected. In the case of products using recycled material, raw materials can have a lower cost. This is due to the additional costs of dismantling, separating and transforming the waste. On the contrary, there are no additional charges on raw materials extraction or CDW disposal in landfill. This last issue should be tackled, as specified in the Galicia Circular Economy Strategy 2019–2030 [94], although this measure is planned to be implemented in some regions [99].

With reference to concrete using recycled aggregate, there might be a lack of production and supply in the vicinity of the work or the region itself. Besides, the CDW recovery plants might not exist to manufacture recycled concrete aggregate in the concrete plant environment. In view of these conditioning factors, environmental impacts of transportation can exceed the benefits achieved through the measure itself [67]. The drawbacks might come up in relation to sustainable products, such as products using recycled material, sustainably managed wood, industrialized components, etc. For this reason, it is advisable to check availability in the environment around the site work before ordering in the contracting specifications.

There are also other scarce and scattered products on the market, such as eco-products guaranteed by Type I eco-labelling. To make their demand feasible in the GPPBR, it would be necessary to create an updated registry of sustainable products to easily identify companies [67] that market them. In addition, the continuous evolution of the market makes it necessary to permanently review measures related to eco-products, reused or renewed products. There may even be regulatory changes such as the introduction of requirements on recycled content in the Regulations for Construction Products [3].

There are also difficulties in collection by suppliers of products, containers and packaging for reuse or recycling. This measure requires the product supplier to guarantee logistical facilities for reuse or recycling. If not, the supplier should deliver waste to an authorized manager. However, this practice can increase environmental impact due to transportation.

Finally, bringing in reused products with a short useful life can cause negative effects, since this implies an early replacement or repair. Thus, to propose this measure, useful life of products in their new use should be considered.

#### *4.2. How to Apply the GPPRB in the Rehabilitation of Historic Buildings?*

To the difficulties mentioned above, some limitations must be added in interventions within historic buildings. In this case, instead of indiscriminately applying criteria established in the GPP, the contracting bodies should draw up a detailed study of each building requiring, if appropriate, advice. In general, feasible measures should be implemented, with flexibility in case they conflict with the essence of the building itself and, if appropriate, compensate with additional measures. Likewise, communication between all those involved in the rehabilitation should be fostered in order to better integrate environmental criteria.

#### *4.3. Does Public Procurement Itself Favour Sustainability and Innovation? How to Increase the Participation of Small and Medium-Sized Enterprises (SME)?*

Barriers are also observed in the technical terms proposed in procurements, which prevent environmental criteria from having a greater impact on proposal evaluation. Therefore, it may be appropriate to increase the relevance of these measures in valuation criteria, so that the total cost is not higher than 50%, so as not to be decisive for tenders.

On the other hand, as shown in the results, a greater impulse of the GPPRB is achieved when environmental measures are mandatory through normative provisions. To this effect, it is necessary that measures are linked to the subject of procurements, and clearly defined in procedures.

In the current frame of economic recession, SMEs are the driving force for the economy [113]. So as to prevent SMEs from being left out of larger procurement, and consequently limit the number of lots awarded to the same company, procurements can be divided into batches. Likewise, to contribute to economic development and job creation in regions during procurement execution phase, it is advisable to invite regional SMEs involved in the innovation sector linked to sustainability [113]. In this sense, to promote the public procurement of innovative solutions, various Administrations should provide support to companies and research institutions, able to provide technological solutions or advice on innovation.

#### *4.4. Do Public Administrations Meet Their Own Challenges?*

Public procurement opens up a great opportunity to renovate buildings according to principles of energy efficiency and circular economy. Additionally, this task is complex, time passes and not all administrations seem to keep up with the ambitious goals set. Generally, an administration efficient enough to speed up long procurement processes is needed.

Regarding the improvement of the GPPBR, the Administration can undertake actions in nearly all areas: information, coordination and monitoring, training, awareness, dissemination, as well as financing (Figure 13).

#### 4.4.1. Is There Quality Technical Information to Guide the GPPBR?

Generally, the information source found is scattered in different documents, and there are few specialized guides in the GPPBR. Due to this, it is vital to draft specific guides for an easy and feasible incorporation of environmental measures in the GPPRB, according to the type of building (teaching, administrative, health, etc.).

The proposed measures should be well-defined to clearly understand how they can be met and verified in the different phases of the GPPBR. With regard to the latter, some guides mentioned above [67,69] already include more precise and detailed information. Furthermore, with a better definition, consultations or revisions that might lengthen procedures could be avoided [114].

It would be very useful if measures had associated indicators, objectives or guidelines, such as value for money, cost-effectiveness, impact on the total cost of investment, savings generated, technologies involved, implementation period, number of citizens affected, etc. In this way, there would be criteria to bring in measures according to the type of work. Additionally, product performance suggested should be linked to its final functionality, for example photocatalytic effect, bactericidal or bacteriostatic surfaces, etc.

In order to become more functional, measures should include references to web sites or other guides for further information, and also a provision of good practices with real cases of application. It would also be desirable to connect measures with supplying companies that could evaluate practice and generate an "e-marketplace". In addition, to facilitate the implementation of GPPBR measures in small towns, regional administrations should draft sheets with practical, useful and schematic information to help suppliers make decisions, all based on a Think Tank for each municipality. If the contracting body did not have sufficient resources, it could hire a consulting service to better define measures according to the type of building, needs, environmental commitment or relationship between environmental benefits and economic costs.

In general, with regard to viability of environmental measures related to products, it is essential to know in advance the regional market in terms of construction products, especially the innovative ones. Furthermore, innovative measures need to enable better solutions with optimized costs [115]. For example, in the PPI strategy of the Junta de Andalucía, public tender processes are highlighted to promote start-up markets [116]. Likewise, progress should be made in research to propose the most effective measures considering the life cycle approach, and thus find optimal solutions in building renovation. For example, Level (s) is the EU tool recommended for integrating life cycle assessment into GPP [3]. Moreover, given the growing number of certification systems for building sustainability, they could be regarded as a reference.

Finally, it would be practical to have digital guides for updating and improving measures on a regular basis. In addition, it would be very convenient to add monitoring and inspection of environmental measures to procurements. In this connection, effectiveness and implementation could be easily verified, as well as identifying shortcomings that can improve environmental performance.

4.4.2. From Theory to Practice: Is There Sufficient Coordination among Public Administrations? How to Detect if Tools Are Being Applied?

To increase effectiveness of actions, joining forces is essential, along with coordination by different administration departments, and the different administrations, as well as implementing the monitoring of actions realized.

Because of the political organization of Spain at a territorial level, a large part of the definition in the programs for GPP, implementation and monitoring is performed by the regions themselves. This decentralization enables regional administrations to draw up laws, regulations and guides within the state regulatory framework, resulting in a large amount of documentation, as mentioned above. This requires well-trained professionals and a high level of organization. For this reason, and due to the different resources of regions, greater collaboration and coordination between these and the State should be desirable. Certain aspects of the GPPBR could be addressed centrally: for example, by setting

up a national agency in which all regions were represented to support procurement authorities through guidance, training, and documentation as a common reference, especially guides. Based on them, regional administrations could draw up additional papers to address specific aspects of each area, if necessary. Thus, these tools could enhance the different regional economic bases, support specialization of various productive sectors and favor local products.

On the other hand, within the scope of the General State Administration, an interministerial commission was set up to bring criteria into the GPP [35]. In the same vein, it is necessary to create an interdepartmental committee for each region, in order to coordinate the onboarding of ecological criteria, development of strategies for GPP and monitoring.

With the aim of detecting the degree of implementation of the GPP goals and execution of actions, an annual monitoring concerning the application of environmental measures in the public procurement awarded should be carried out [89,117]. For this purpose, the interdepartmental committee should add results provided by departments for the GPP, with results provided in a standardized format or use platforms and tools for integration [118,119].

Regarding specific measures, for environmental enhancement check-up during the use phase of the building, actions such as checking consumption or conducting a survey for building users to analyze the perception of comfort should be undertaken [70]. A key factor in the environmental impact of buildings is energy use during occupation. The monitoring of CDW management would be required, since waste traceability is lost due to proliferation of illegal dumping [120].

#### 4.4.3. Is There Enough Training for Professionals to Be Qualified?

One of the main problems detected for measure implementation is a lack of training for all professionals involved in the GPPBR process. Given the novelty and complexity of the subject, particularly in aspects related to the circular economy, it is needed to boost actions for an exchange of technical knowledge. Staff training in environmental criteria is one of the first steps to increase their incorporation into contracts.

For all this, training plans on environmental measures should be proposed, as well as tools developed, as part of procurement documents, including cases of good practice. In particular, emphasis is needed on the relevance of specific energy training plans and eco-labelling product presentations, given that both construction companies and designers should familiarize with these [41,69]. Training administration staff in the "Building Information Modeling" (BIM) work methodology is essential. This methodology is a requirement for public funding projects. At the State level, an Interministerial Commission was created for bringing BIM methodology into public procurement [121].

#### 4.4.4. Are We All Sufficiently Involved?

A solid communication plan of actions carried out in the GPPBR can maximize impacts, by setting up web platforms to ensure visibility of hiring. Thus, the EU GPP Good Practice [122] platform presents success stories, in which improvements are emphasized, which is a feature inspirational for their replicability.

Likewise, in order to gain complicity of citizens, tools should be created to communicate the beneficial effects of the GPP. For example, an information panel could be displayed on energy efficiency actions, renewable production and other circular economy measures applied [37]—the same as in certain public buildings, where it is mandatory to display energy efficiency labelling [123]. Occupants in buildings could also receive information on carbon footprint over their lifetime, by installing automated systems to obtain data on electricity use, air quality and building waste production. All this leads to awareness raising on environmental impacts generated by buildings and behavior-correction, where appropriate. Additionally, user participation tools can be implemented in the phases of planning, execution and evaluation of the projects, as contributors to needs and ideas [109]. This direct involving encourages a greater acceptance of the results of the GPPBR.

#### 4.4.5. Is Sufficient Funding Planned?

Faced with the serious social and economic crisis caused by the COVID-19 pandemic, in order to access the EU reconstruction funds, we come across both the constraint and opportunity that "the recovery is green". This implies that part of the EU aid must be invested in actions of the Green Deal to combat climate change and achieve the EU decarbonization objective from the present to 2050.

#### **5. Conclusions**

Scientific literature indicates that the GPPBR represents an opportunity to implement environmental policies in a prominent activity such as public procurement in construction—a key economic sector in Spain. However, this analysis concludes that the inclusion of environmental measures in public procurement for building rehabilitation is low, and the total costs continue to be weighted much higher than environmental criteria. Among the possible causes of this scenario, various studies note a lack of knowledge of parties involved, because of the absence of practical information, among other reasons.

 By analyzing this documentation, it was possible to collect a large amount of information in the form of environmental measures to bring in the GPPBR specifications. It is worth noting the difficulty in finding specific and quality information on environmental measures to be incorporated into the GPPBR. Most instruments refer to GPP generically.

The study shows the need to develop advanced technical procedures. It is evident that these should compile ecological measures to put into practice in the GPPBR with a required level of definition. This way, the agents involved will understand how to comply with them and verify in the different phases of tender procedures. From the information consulted, the great support found in references to real cases of good practice, and even specific guides for further information is remarkable. It is also noted that if measures were associated with indicators, contracting authorities could add to them with better criteria. In addition, the information on the feasibility of applying measures is a key factor, since there might be barriers that should be detected before being proposed in the tender specifications.

It is found that the Administration plays a vital role in promoting the GPPBR. There can be no doubt that environmental measures are incorporated, and monitoring is carried out when there are regulatory provisions that comply with them. Additionally, with greater collaboration and coordination between regional administrations and the State, there would be sufficient resources to develop the mentioned technical procedures, especially guides. These could serve as a reference for regions to adapt to their specific features. Once information on environmental measures has been gathered in the GPPBR, it is essential to make this widely known to professionals and provide awareness and dissemination campaigns for everyone.

Based on this approach to environmental measures includible in the GPPBR, the necessity of future research is significant. A detailed study could be made on environmental measures in the procurement specifications of regional public administrations, as well as their assessment. It is also considered worthwhile to identify what the most effective strategies are after application, with an analysis of the results. Delving into research on good practice examples is always encouraging to promote further initiatives. Likewise, it is possible to deepen the analysis of life cycle costs of existing products on the market regarding building renovation, as well as the development of innovative products. Eventually, an in-depth investigation should be carried out on the real impact of GPPBR environmental measures on the reduction in environmental consequences caused by the constructing sector in Spain.

**Author Contributions:** All authors have contributed equally to the investigation and final manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declared no conflict of interest.

### **Appendix A**

**Table A1.** Papers relating to the GPPBR developed by regional Public Administrations.

**Table A1.** *Cont.*

#### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Article* **The Church Tower of Santiago Apóstol in Montilla: An Eco-Sustainable Rehabilitation Proposal**

### **M. Araceli Calvo-Serrano 1,\*, Isabel L. Castillejo-González 1, Francisco Montes-Tubío <sup>1</sup> and Pilar Mercader-Moyano 2,\***

Received: 29 July 2020; Accepted: 28 August 2020; Published: 31 August 2020

**Abstract:** Is it possible to carry out eco-sustainable rehabilitations on specially protected buildings? This is the main question and starting point for this research. We will use the tower of the Church of "Santiago Apóstol" in Montilla as a case study; with its most remote antecedents in the 15th century, it is an emblematic building of one of the most important cities in the Cordovan countryside and is listed as an Asset of Cultural Interest (*Bien de Interés Cultural* or BIC) as of 2001. The application of eco-efficiency criteria in the rehabilitation of this type of building might stimulate the reactivation of the construction sector in the rural area, positively impacting the promotion of a circular economy. To this end, a general methodology has been established for carrying out eco-sustainable renovations on this type of building, which defines indicators for evaluating the eco-sustainability of such interventions. This methodology is applied to the case study of this important building in Montilla to ensure that a feasible intervention has been proposed, aligned with three basic pillars of sustainability that considers its environmental, economic, and social impact.

**Keywords:** patrimony; tower; buildings rehabilitation; eco-sustainable; sustainable; town planning; resource efficiency; eco-efficient construction solutions

#### **1. Introduction**

The restoration of historical buildings aims to preserve their architectural and artistic elements so that they faithfully illustrate their evolution through history, allowing the history of a building to be read through its architecture. Special attention must be paid when buildings are listed as Assets of Cultural Interest (BIC in Spanish) [1], regulated by the Spanish and Andalusian Historical Heritage laws [2,3].

In order to preserve the beauty of this heritage, it is necessary to indicate the pertinent works of repair, conservation, reconstruction, and restoration. For the intervention in a building classified as Historical Heritage two processes must be carried out: A historical study and a safety evaluation. We wonder if it is possible to carry out a rehabilitation of this type of building while meeting eco-efficiency criteria. In the case of the Church Tower of Santiago Apóstol, multiple interventions have been carried out over the years. The last one was executed in 1989, and an additional conservation intervention would be necessary shortly after.

We think rehabilitation and eco-sustainable interventions on specially protected historical buildings can be key to reactivating the construction sector and general economy in rural areas. For decades, these regions have suffered from depopulation. As a result of the health and economic crisis in which we find ourselves today, a return of the population to these areas is highly plausible, with all that this may entail. The application of strategies and methods in the field of eco-sustainability, while respecting

the environment and the impact on buildings, will also favor the flow of human, material, and financial resources in the area, generating employment and promoting tourism in the region and bolstering its economic development.

In the enhancement of these architecturally and historically relevant buildings, we understand that two essential aspects must be considered: Materials and eco-sustainability. The physical qualities of the materials used (texture, shine, surface, appearance, etc.) must be in line with the space, awakening the senses of its viewer, integrating the renovated portions with the history of the building and the environment [4,5]. The materials used will play a fundamental role in the eco-sustainability of the rehabilitation. Carrying out the intervention from an eco-sustainable point of view will reduce not only energy consumption, but also the impact on the environment and the generation of waste.