Sustainable Building in Catalonia: Recycling, Energy Efficiency and the Circular Economy in Construction

1. Introduction

The construction sector is a major contributor to global waste generation; specifically, it accounts for 36% of solid waste [1]. This highlights the need for sustainable management of construction and demolition waste (CDW) as a pressing environmental challenge [2]. Furthermore, the circular economy (CE), moving away from the linear ‘use and throw away’ model, is shifting towards strategies focused on waste reduction, reuse and recycling. CDW is fundamental to the transition to a circular economy in construction, and this study presents tools for achieving this circularity, such as concrete recycling, digital tools including Building Information Modelling (BIM) and Life Cycle Assessment (LCA), amongst others, to optimise waste management, its cost barriers and the regulatory challenges faced by European countries, along with their technological limitations. The research analyses circular economy (CE) case studies in CDW management, using business models to accelerate the construction sector’s transition to a circular economy, thereby reducing environmental impact in line with the Sustainable Development Goals (SDGs). The construction sector and the recycling of materials are essential for moving towards a circular model in line with the Sustainable Development Goals (SDGs) of the 2030 Agenda [3].

In the construction sector, recycling of materials is essential to move towards a more circular economic model in line with the Sustainable Development Goals (SDGs) of the 2030 Agenda. It is worth noting that the SDGs benefit from the circular economy, and the circular economy benefits from the SDGs, in particular SDGs 6, 7, 8, 12 and 13, which include clean water and sanitation, affordable and clean energy, decent work and economic growth, responsible consumption and production, and life of terrestrial ecosystems. In this context, recycling of construction materials has a significant environmental impact, and it is imperative to focus on reducing energy consumption and the carbon footprint it causes, as a key objective of the 2019 European Green Deal [4].

The construction sector therefore requires a more sustainable approach, using recycled materials and reducing energy consumption to lower its carbon footprint, as it is a sector characterised by high consumption of natural resources, significant greenhouse gas (GHG) emissions and high levels of waste generation. By using recycled materials, these impacts can be mitigated, and through more efficient energy consumption and construction techniques such as passive building design, amongst others, progress is being made towards the CE model [4], with a positive economic and social impact [1].

The sector must move towards a more circular economic model involving the reuse of materials and the use of recycled materials to reduce demand for new natural resources whilst generating less waste. To achieve this, it is necessary to transform waste into new resources, increasing the efficiency of available resources and utilising local resources, as well as recycling the materials used [5,6,7].

In the initial scenario, the utilisation of recycled materials serves to diminish the demand for natural resources, as recycled steel, concrete and wood conserve raw materials (such as water, trees and minerals) that prove beneficial to terrestrial ecosystems. The recycling of construction materials serves to advance the principles of a circular economy, whereby materials are reused and reintroduced into the production cycle. This encompasses a range of materials, including concrete, steel and wood, which can be recovered and reused in new construction projects. This strategy has the additional benefit of reducing the number of landfills and instances of soil contamination. Furthermore, the use of recycled materials improves the thermal insulation of buildings, reduces the demand for energy for air conditioning, reduces the heat derived from asphalt and cement, and allows for the use of low-carbon concrete, recycled composite materials, and bioplastics, which are more energy efficient, more durable, and have superior acoustic and thermal properties [8,9].

In this regard, governments implement regulations pertaining to the utilisation of recycled materials in construction, employing a range of measures including tax incentives, green certifications and energy efficiency regulations, with the objective of reducing the carbon footprint. In accordance with European Union directives, the regulations that promote the use of recycled materials in construction include the Technical Building Code (CTE) (2019), the Waste and Contaminated Soil Law (2022), the Spanish Circular Economy Strategy (EEEC), as well as ecological certifications, tax incentives and direct aid, such as the Recovery, Transformation and Resilience Plan (Next Generation funds from the EU). These are financial incentives for the rehabilitation of buildings using recycled materials, as well as for the energy rehabilitation of buildings and projects that utilise recycled and sustainable materials. It is also noteworthy that the autonomous region of Catalonia has its own regulations to promote the use of recycled materials and sustainable construction, particularly in the context of public buildings and infrastructure [10].

The latest IPCC report (AR6) states that the construction sector’s contribution to global greenhouse gas (GHG) emissions, in 2019, accounted for 21% of global GHG emissions, and 28% of global emissions stem from the production of construction materials such as steel, cement and glass (embodied carbon) generated during the extraction, processing, manufacturing, transport and installation of construction materials.

According to the European Union, the construction sector is responsible for half of the energy and materials consumed, a quarter of the water used and more than a quarter of the waste. Therefore, the circular economy in the construction sector is a priority, as confirmed by Spain’s Circular 2030 strategy and the new EU Circular Economy Action Plan. In addition, the Next Generation Funds aim to promote the circular economy, especially in the construction sector, since a large number of resources are extracted from it, transformed, used and finally end up in a landfill and recycling these resources is crucial. This requires training, administrative, business, technological and sustainable materials support [11,12].

In this regard, quality labels are a tool for promoting the necessary sustainability of the sector, and, in the case of Catalonia, the RECONS Environmental Quality Label, created in 2020 by the Private Foundation for the Regulation of the Construction Sector in Catalonia (an organisation comprising the Chamber of Construction Contractors of Catalonia and the Guild of Construction Contractors of Barcelona and its Counties), aims to publicly certify the sustainability of construction, renovation and maintenance companies. Housing refurbishment is a reality, and promoting these sustainable practices towards the EC is necessary [13].

Applus+ Group manages the RECONS seal to guarantee commitment to the environment, risk prevention, legal compliance and a balance between economic, social and environmental aspects. Furthermore, this label promotes the reuse of materials, traceability and shared responsibility throughout their life cycle, alongside specific training in construction waste management. This helps to highlight environmental responsibility standards for the transition from the linear model to the CE model.

Given this reality, the aim of our study is to demonstrate which actions and initiatives promote the recycling of construction materials in Catalonia, within small and medium-sized enterprises in the construction sector, and how the transition to the circular economy model, in line with the 2030 Agenda and the European Green Deal, is made visible through labels. The study also highlights the strategies and practices implemented in three key areas: the recycling of construction materials, the adoption of energy saving certificates (CAEs), and the incorporation of passive design in building construction. Specifically, recycling, energy efficiency and design itself reduce greenhouse gas emissions, moving towards a circular model.

It is worth noting that, in the construction sector, recycling aluminium can reduce the energy required to produce new aluminium by 95% [14,15]. Incorporating recycled materials into construction processes can reduce the carbon footprint. Furthermore, the use of CAEs, as well as passive building design, reduces energy consumption over the building’s lifespan (through the management of temperature, ventilation and hot water) and the use of natural resources (natural lighting, efficient solar orientation, thermal insulation, controlled ventilation with heat recovery and temperature-stabilising materials) reduces the carbon footprint. Furthermore, solar shading and natural ventilation are integral aspects of passive building design, which reduce energy consumption and the carbon footprint [16,17].

The methodology employed in this study is exploratory and highlights the strategies of the construction sector to move towards the circular economy model through actions and initiatives in this direction. Case studies of companies in the construction sector in Catalonia are presented to identify strategies and practices implemented in three areas: the recycling of construction materials, the adoption of energy saving certificates (CAEs), and the incorporation of passive designs in buildings, all with the aim of reducing the carbon footprint for progressive decarbonisation.

Following the introduction, the literature review and the empirical part of the study are presented, along with the results, their discussion and the conclusions of the research.

2. Materials and Methods

2.1. Literature Review

The academic literature covers the recycling of construction materials to reduce the carbon footprint, as well as energy performance certificates in construction and passive building design to lower the carbon footprint in the construction sector.

In terms of building materials and energy efficiency, both new and existing buildings consume large amounts of energy and resources. Specifically, in existing buildings, measures are taken to minimise energy consumption and recycled materials are used when circular economy models are followed [18]. In other words, for new constructions and the maintenance of existing ones, it is necessary to move towards the circular model by recycling materials and increasing energy efficiency, despite political and legal barriers, EU harmonisation issues, and depending on the decisions of national and local governments [18]. Other studies have identified various barriers that hinder the incorporation of the circular economy in the construction sector, particularly in projects using timber, a key material for reducing the carbon footprint. Among the main limitations are a lack of knowledge and awareness, regulatory constraints, market dynamics and technical complexities. Consequently, it is necessary to promote a more robust regulatory framework and the implementation of standards that facilitate the transition towards more sustainable construction [19].

Furthermore, the use of recycled materials reduces the sector’s carbon footprint and prevents construction materials from ending up in landfills—a concern highlighted by the World Green Building Council in the construction sector (as construction consumes over 50% of all extracted materials and 35% of its waste ends up in landfills) [20,21]. Therefore, the construction sector must increase the recycling of construction materials by recovering cement, concrete, wood, metals and packaging waste, amongst others. It is worth noting that some construction companies dispose of waste without sorting it, except for metals, which generate a significant carbon footprint [20].

Some measures are key to reducing this carbon footprint. Building demolition waste can be used as an alternative aggregate for construction, and by incorporating these recycled aggregates, the use of new resources is reduced. The use of recycled aggregates in concrete thus contributes to the sustainability of the construction sector. The composition and morphology of recycled aggregates differ from natural aggregates, but the incorporation of pozzolanic materials and various pretreatment techniques improves the quality of the concrete [21,22]. In addition, recycled aggregates from construction and demolition waste affect the mechanical properties of concrete (strength, compaction and durability), and pozzolanic materials improve the density and durability of concrete. Recycled concrete is therefore an excellent option for the construction of buildings, stadiums and swimming pool walls, for example, by reducing the need to extract and produce new concrete [23,24,25,26].

Importantly, the durability of these recycled materials ensures a longer lifespan for buildings, stadiums and swimming pools, further contributing to circularity [27,28]. One of the recycled materials widely used in swimming pool construction is recycled concrete, which is crushed and processed before construction, requiring less energy and water resources and resulting in a lower carbon footprint [21].

In addition, cement coating improves the quality of concrete, making it stronger and more durable with a lower environmental impact. For example, combining up to 30% recycled aggregates with pretreatments and pozzolanic materials produces higher quality concrete, which improves waste management in construction and reduces the carbon footprint [21].

Thus, managing waste through demolition and reuse brings the sector closer to circularity, in line with the 2030 Agenda and the European Green Deal. This management is not without awareness-raising and training strategies within the sector [29], as the construction and demolition waste used does not harm the environment and brings us closer to the climate neutrality target of the European Green Deal for 2050. Specifically, Australia generated over 27 million tonnes of this waste between 2018 and 2019, and only 50% of it was recovered, partly due to barriers created by non-standardised sustainability regulations across countries [30].

Furthermore, at landfill level, the recycling of construction materials would reduce overall landfill waste by 35%, although further research is needed into the recycling of different types of construction waste due to their high carbon footprint [21,31], which must be reduced in order to achieve a more circular model and greater corporate social responsibility within the sector [21].

It is worth noting that the reduction in the carbon footprint through the recycling of construction and demolition (C&D) materials is not uniform across all countries or all construction companies and varies [32,33,34]. Furthermore, the recycling of construction waste requires appropriate technologies and infrastructure, as well as raising awareness of recycling in line with the challenges of the 2030 Agenda [29,30]. Studies on carbon emissions from buildings vary geographically (China, USA, Europe) and in terms of construction material recycling [35].

To reduce the carbon footprint in the construction sector, greater energy efficiency in construction is also required. To this end, the Energy Saving Certificates (CAEs) Scheme in Spain, as an instrument that enables obligated parties to meet their energy-saving targets by submitting certificates attesting to the effective reduction in final energy consumption, offers a flexible and economically accessible alternative to financial contributions to the National Energy Efficiency Fund, incentivising investment in energy efficiency measures by enabling the monetisation of the savings generated and their transfer to third parties [36]. Energy Saving Certificates (CAEs) are therefore a regulatory instrument within energy efficiency policies that officially certify the amount of energy that has been saved through the implementation of efficiency improvement measures. Each certificate generally corresponds to a unit of energy saved —usually expressed in kilowatt-hours (kWh)— achieved through measures such as the energy refurbishment of buildings, the replacement of equipment with more efficient alternatives, or the optimisation of industrial processes. These certificates form part of a market-based system that enables the quantification, verification and, in certain cases, trading of the energy savings achieved, thereby contributing to the fulfilment of European targets for reducing energy consumption and greenhouse gas emissions [37].

Other studies focus on reducing carbon emissions in building construction through an integrated strategy based on Life Cycle Assessment (LCA), using a methodology that divides buildings into structure, envelope, interior and exterior, thereby enabling the identification of high-carbon materials and promoting the use of Environmental Product Declarations (EPDs), to facilitate the comparison of low-carbon construction practices and materials. Furthermore, in the early design phases, carbon reduction measures lower emissions as a key strategy in the sector, and the carbon footprint of the exterior envelope is included in the total carbon footprint calculation to decarbonise the construction sector [38].

Other research identifies four main areas in the decarbonisation of the construction sector: optimising energy efficiency, managing carbon throughout the entire life cycle of buildings, transforming urban systems and integrating smart technologies, with future interdisciplinary approaches to develop comprehensive carbon-neutral technologies, smart solutions, simulation tools and increase the use of renewable energy [39].

Furthermore, passive building design at the architectural level is key to decarbonisation; specifically, building using bioclimatic design, thermal insulation, heat-recovery ventilation, airtightness, the elimination of thermal bridges, and high-performance building envelopes reduces the carbon footprint [40]. This passive design implies sustainable development, as it provides greater energy efficiency (SDG 7), addresses climate change (SDG 13) and promotes sustainable cities (SDG 11). Furthermore, the integration of these principles into the design and construction of buildings creates sustainable, healthy and resilient environments in the face of climate change. [41]. Thus, a construction model in harmony with the Sustainable Development Goals (SDGs) brings the construction model closer to circularity through passive design in tune with renewable energy (SDGs 7 and 13); the use of sustainable and recycled materials (SDGs 12 and 15); demountable designs and the recycling of construction and demolition waste (SDGs 11 and 12); as well as managing water resources more efficiently (greywater and rainwater) (SDG 6) and improving indoor air quality (SDG 3) [42]. If buildings can be made affordable and accessible (SDGs 10 and 11), through good urban planning (public transport, cycling and walking), with green spaces and ecological corridors (SDGs 9 and 11), this promotes the circular economy, facilitates maintenance and extends the useful life of buildings whilst reducing the carbon footprint (SDGs 12 and 13) [43].

A major barrier to addressing these challenges is the variation in regulations across different geographical areas, with no common standardisation within the European Union [18]Furthermore, there is currently still not a high level of recycling and reuse of materials, although companies are encouraged to adopt waste management practices [44]. This requires investment in advanced technologies, the costs of which represent another significant barrier, necessitating intervention by the public sector [44,45]. Furthermore, education, training, awareness-raising and the implementation of sustainable development policies are barriers that can be overcome [45,46].

Finally, it should be noted that sustainable construction is promoted through certifications that accredit sustainable buildings, in line with the World Green Building Council (WorldGBC), which certifies sustainable buildings worldwide and promotes sustainable construction practices [47,48,49]. Specifically, the WorldGBC participates in various green and sustainable construction projects worldwide [47,48,49,50]and promotes sustainable building certifications, such as Leadership in Energy and Environmental Design (LEED), which assesses the sustainability of buildings in terms of energy efficiency, use of materials, indoor air quality and other aspects [51,52]. These certifications can lead to tax incentives and further research in this field regarding energy efficiency, sustainable materials and bioclimatic design [52,53]. The WorldGBC also offers educational resources for construction professionals, architects, engineers and other interested parties [54] to promote sustainable construction and address existing environmental and climate challenges [49]. Other certificates of this type include the energy-saving certificates in construction.

3. Methodology and Results

By applying a case study methodology to companies in the construction sector in Catalonia, the aim is to identify and highlight the strategies and practices implemented in three key areas: the recycling of construction materials, the adoption of energy saving certificates (CAEs), and the incorporation of passive design in building construction. These actions are aimed at reducing the carbon footprint of buildings and promoting a circular economy model in the construction sector, thereby contributing to its progressive decarbonisation. The academic literature recognises that construction is one of the sectors with the highest resource consumption and greenhouse gas emissions, which underscores the importance of implementing sustainable strategies [55,56,57]. In this context, the integration of energy efficiency measures, waste recycling and passive design not only helps to mitigate environmental impacts but is also complemented by specific certifications that attest to the sustainability of projects and promote the transition towards a circular model in construction. Rapid urbanisation and the transition to a low-carbon economy require the integration of sustainability criteria into the construction sector, which accounts for approximately 36% of CO₂ emissions in the European Union.

Regarding the recycling of construction materials, the case study on the circular economy in the construction sector in Catalonia combines the refurbishment of the Spotify Camp Nou and the involvement of the company Cementos Molins. During the demolition of the old stadium, concrete and steel were recovered, which were crushed and sorted to produce recycled aggregates, reused in earthworks, non-structural concrete and, to some extent, in structural concrete, in accordance with current regulations [58]. To this end, a temporary recycling plant was installed on the Miniestadi site, enabling waste to be processed directly on-site and minimising transport. At the same time, Cementos Molins applied its industrial waste recovery model, reincorporating more than 140,000 tonnes of construction and demolition waste into the production of concrete and cement [59,60]. These initiatives demonstrate how the recovery of materials and the reintroduction of waste into the production cycle contribute to closing the resource cycle, reducing landfill use and minimising the environmental impact of large-scale construction projects. In the case of Catalonia, 33% of the waste generated comes from construction, and 40% of this ends up in landfills [61]. Therefore, the construction sector in Catalonia must promote the circular economy; through the recycling of construction materials, energy-saving certificates, passive building design and certifications, it can drive sustainable construction.

From an academic and sustainable engineering perspective, the management of construction and demolition waste (CDW) is a critical component of the sustainability of building and civil engineering projects. Recent scientific literature highlights that responsible CDW management (covering planning, reduction at source, reuse, recycling and traceability) is essential for moving towards sustainable construction models and reducing the environmental impact of projects’ life cycles. For example, studies on the circular economy integrated into construction waste management emphasise the need for systemic approaches that link construction planning with technologies for the reuse and recovery of materials.

Energy Saving Certificates (CAEs) are a form of ‘financial recognition’ for energy that is no longer consumed, providing an incentive for companies to invest in measures that reduce energy consumption. In Spain, this system was introduced by Royal Decree 36/2023 and is designed to enable savings in kilowatt-hours of energy to be converted into tradable assets to meet legal energy efficiency obligations or generate revenue through their sale. From a legal and economic perspective, ESAs align with the objectives of the European Union’s Energy Efficiency Directive (EED), which requires Member States to promote measures aimed at reducing energy consumption and cutting greenhouse gas emissions in line with the European Green Deal. In the field of academic research, concepts analogous to CAEs are ‘tradable certificates for energy savings or market instruments that assign ownership rights to the energy savings generated by efficiency measures, facilitating their exchange between economic agents and reducing the total costs of meeting efficiency and climate mitigation targets. A central pillar of ESCOs is the measurement and verification of energy savings, as a necessary condition to ensure that the certificates issued represent reductions in energy consumption, backed by reliable verifications. Furthermore, these mechanisms require energy audits and energy management systems that identify and quantify savings, to promote measures such as equipment replacement, energy improvements in buildings and the optimisation of industrial processes. Recent studies in Europe emphasise that the combination of audits and investments in energy efficiency reduces greenhouse gas emissions.

Since its launch, the CAEs system has generated quantifiable results in terms of energy savings and economic activity. Official reports show that, up to the start of 2025, around 1,988 GWh of cumulative savings have been recorded in Spain, and particularly in Catalonia. In terms of economic impact, the implementation of CAEs has generated additional revenue for companies participating in the scheme through the sale of certificates, which can improve the profitability of energy efficiency projects and incentivise investment in low-consumption technologies. This aspect aligns with the achievement of decarbonisation and industrial competitiveness targets. Whilst CAEs represent a policy innovation, their optimal design and long-term effectiveness depend on technical, regulatory and market factors. Within the framework of meeting energy efficiency targets and generating Energy Saving Certificates (CAEs) in Catalonia, we analyse an industry that replaces 250 2×58 W fluorescent lights with 48 W LED luminaires, with an investment of 35,000€. Given that the lights operate 24 hours a day throughout the year, and the price of electricity is 0.12€/kWh. With an electricity mix emission factor of 0.283 kg CO₂ eq/kWh.

We are looking at the annual energy savings resulting from replacing fluorescent lights with LEDs. The annual financial savings resulting from the replacement at a price of 0.12€/kWh. The reduction in the carbon footprint with the specified electricity mix. The payback period. The monetised energy savings from the PPA, given that the PPA price is 0.11€/kWh. And the payback period with a PPA (Table 1).

By switching from 116 W to 48 W luminaires, total consumption decreases by 148,920 kWh per year, at an energy price of 0.12€/kWh, representing savings of 17,870.4€ per year. Furthermore, with an electricity mix of 0.283 kg CO₂ eq/kWh, 42.1 tonnes of CO₂ are avoided per year. The investment of 35,000€ is recouped in 1.96 years, but with the CAEs generating 16,381.2€, the payback period is 1.04 years.

Passive design in building construction in Catalonia helps to reduce energy consumption and CO₂ emissions in the construction sector through architectural strategies that make use of local climatic conditions and minimise the need for active climate control systems. These methods include appropriate solar orientation, high-efficiency thermal insulation, airtight building envelopes, thermal bridge control and the use of natural or mechanical ventilation with heat recovery (concepts incorporated into standards such as Passivhaus). Recent studies show that implementing these criteria in Mediterranean climates can achieve significant reductions in energy demand for both heating and cooling, helping to meet the energy efficiency targets set out in the European Union (EU) directives for nearly zero-energy buildings. In Catalonia, where energy-efficient construction is growing steadily, there are specific projects that demonstrate the technical and economic viability of passive approaches. A notable example is Terrassa Haus, the first Passivhaus-certified multi-family building in the city of Terrassa, which incorporates high-performance thermal insulation, airtightness validated through blower door tests, and a design focused on thermal comfort, achieving stable indoor conditions with low energy consumption, serving as a regional benchmark for passive architecture applied in a Mediterranean urban context. Furthermore, in Catalonia, single-family Passivhaus Plus projects have been developed, such as K-Igualada in Igualada (Barcelona) [62], where low heating and cooling demand is achieved through passive envelope design, the use of timber as a building material, and solar control strategies adapted to the Mediterranean climate. Recent academic research, such as that by Echarri-Iribarren et al. (2024) [63], analyses key elements of Passivhaus buildings on the Spanish Mediterranean coast, such as heat recovery units integrated into mechanical ventilation systems, which contribute to the efficient renewal of indoor air without compromising the building’s overall energy demands.

Passive design, therefore, not only provides quantifiable energy benefits but also improves thermal comfort and indoor air quality, and aligns with urban sustainability goals. Recent literature highlights the need to adapt passive strategies to the local climate, optimising aspects such as solar control in summer and adequate ventilation throughout the year to maximise efficiency and comfort in Mediterranean buildings. The incorporation of passive building design into contemporary architecture is an essential component of the Sustainable Building Model, aimed at reducing the carbon footprint and meeting the Sustainable Development Goals (SDGs). In this context, the Passivhaus standard, developed by the German-based Passivhaus Institut, stands as an international benchmark for achieving high energy efficiency in buildings through passive strategies that minimise energy demand for heating and cooling, without compromising indoor comfort.

The standard requires specific technical criteria, including a maximum heating and cooling demand of 15kWh/m²·year, primary energy consumption of less than 120 kWh/m²·year, and an air infiltration rate not exceeding 0.6 air changes per hour. These requirements enable Passivhaus-certified buildings to achieve excellent thermal and energy performance compared to conventional constructions [62,63,64].

In Catalonia, interest in Passivhaus has been growing, particularly given the Mediterranean climate, characterised by mild winters and hot summers. Various public policies and funding programmes, such as the Strategic Plan for the Energy Renovation of Buildings (PREE) and the Next Generation EU funds, have promoted energy renovation and the adoption of high-performance standards, including Passivhaus [62,63,64]. Likewise, local authorities are implementing tax incentives, such as rebates on the Tax on Construction, Installations and Works (ICIO) for projects that incorporate sustainable solutions and energy efficiency. The Barcelona Energy Improvement Plan (PMEB) exemplifies this public policy by offering grants for buildings that meet efficiency criteria and reduce emissions, explicitly recommending the Passivhaus standard.

The practical application of the Passivhaus standard in Catalonia can be seen in various flagship projects. Among these, Les Vinyes stands out: a social housing development in Sant Cugat del Vallès that has achieved a reduction of up to 75% in heating demand compared to traditional buildings. The Escola Montserrat in Navarcles, built to Passivhaus criteria, has optimised both energy consumption and occupant comfort. In Girona, the Efficient Office Building incorporates openings and passive design that maximise solar gain and the use of natural light. Meanwhile, a Passivhaus building in Lleida combines a south-facing orientation, thermal insulation, triple-glazed windows and mechanical ventilation with heat recovery, achieving reductions of up to 90% in energy consumption compared to conventional buildings. Furthermore, Passivhaus renovation initiatives are underway in towns such as La Garriga, and professionals certified by the International Passive House Association (iPHA) are actively contributing to the design of sustainable buildings.

In short, the Passivhaus standard is in line with the transition towards a low-carbon economy in Catalonia and represents a building model adapted to the Mediterranean climate, positioning the region as a leader in Spain in energy efficiency applied to sustainable construction.

Furthermore, the RECONS certification (an acronym for Environmental Responsibility in Construction in Catalonia) is a voluntary, sector-specific label promoted by the Fundació Privada per a l’Ordenació del Sector de la Construcció a Catalunya, together with the Gremi de la Construcció de Barcelona and the Cambra de Contractistes d’Obres de Catalunya. This accreditation distinguishes construction companies that demonstrate a verifiable commitment to environmental management, in particular the responsible management of construction waste, the planning of its generation and the implementation of measures for its monitoring and control in accordance with the regulations applicable to the construction sector. The RECONS seal is designed as a tool for transparency and recognition of good environmental practices in a sector traditionally intensive in terms of resource use and waste generation, thereby contributing to the reinforcement of sustainability and circular economy criteria within construction processes. In addition to enhancing the reputation of certified companies, it is hoped that this seal will positively influence public and private procurement decisions by providing evidence of environmental commitment.

Academically, it is important to situate RECONS within the broader trend of environmental certifications and management systems applied to sustainable construction, which are explored in specialist publications. Such research typically analyses how certification processes (BREEAM, LEED and other voluntary building standards) incorporate environmental, social and resource management criteria, in line with the RECONS label, to promote the prevention of negative environmental impacts and encourage responsible practices within the sector. In Catalonia, the adoption of specific certifications such as RECONS responds to regulatory and market pressure towards environmental sustainability, driven both by regional policies (such as the focus on the circular economy and waste recovery) and by demand from consumers and developers for more responsible construction practices. The certification also helps to raise the profile of companies that adopt proactive approaches to environmental management, complementing technical and mandatory standards such as the final waste management certificates required by the authorities for public and private works. Specifically, in an energy-efficient refurbishment project in El Masnou, a company (with RECONS certification) installed insulation on the building’s façade to improve thermal comfort; furthermore, the materials removed during the works were sorted and subsequently transferred to a waste management company for proper treatment. This approach by the Foundation for the Regulation of the Construction Sector is particularly valued in the case of small contractors, especially for the correct sorting of construction waste. This practice not only promotes the sustainable management of materials but also generates economic benefits, such as lower waste treatment fees, the refund of the associated municipal tax, and greater social recognition and added value for the client. Thus, SMEs in the renovation sector reduce their environmental impact by pre-sorting waste; specifically, a construction firm in Bages (RECONS-certified) by sorting materials such as wood, scrap metal or electrical appliances before work begins and sending them to authorised waste management operators specialising in selective collection within the construction sector, thereby reducing its carbon footprint and mitigating the climate impact in the construction sector. And this practice is becoming more widespread as it promotes the shared desire of businesses, citizens and public authorities to achieve proper waste management in the construction sector.

4. Discussion of the Results

The case studies analysed in construction companies in Catalonia highlight strategies and practices implemented in three key areas: the recycling of construction materials, the adoption of energy saving certificates (CAEs), and the incorporation of passive design in building construction.

The actions and policies promoting the recycling of materials in the construction sector within these companies align with the circular economy model, through measures that reduce the carbon footprint with a view to decarbonising the sector, in line with the climate neutrality target set by the European Green Deal for 2050.

Construction materials have a significant environmental impact, as is the case with cement, and their recycling is also a priority for the decarbonisation of the sector, as evidenced by the first case. These actions demonstrate that the circular economy in construction is viable on a large scale, generating environmental, economic and technical benefits; although its consolidation requires regulatory, technological and market advances. Furthermore, this case suggests that the circular economy in construction is not only based on recycling materials, but on spatially and logistically reorganising the production system, where coordination between stakeholders and the minimisation of resource movement become key determinants of sustainability. Moreover, reusing and recycling materials reduces the demand for natural resources and prevents them from ending up in landfills.

Regarding CAEs, the second case highlights the importance of Energy Saving Certificates (CAEs) as an effective energy policy instrument. In the case analysed, the replacement of fluorescent lighting with LED technology generates significant energy savings under continuous operation, reducing both electricity costs and CO₂ emissions. Monetising these savings through ESAs improves the return on investment and acts as an incentive for the adoption of efficient technologies. At an aggregate level, the cumulative savings reinforce their impact on decarbonisation and industrial competitiveness, consolidating ESAs as a key mechanism for mobilising private investment and correcting inefficiencies in the energy market. Furthermore, reduced energy consumption lowers energy costs and the carbon footprint, in line with Spain’s Circular 2030 strategy [65] and the EU’s New Action Plan for the Circular Economy.

The application of passive design strategies and the Passivhaus standard in Catalonia has demonstrated significant reductions in energy demand and CO₂ emissions, even in Mediterranean climates. Projects such as Terrassa Haus and K-Igualada show that solutions such as high-efficiency building envelopes, airtightness and ventilation with heat recovery enable thermal comfort to be achieved with low energy consumption.

Furthermore, passive design improves indoor air quality and, together with public policies and funding programmes such as the Energy Renovation Plan and the Next Generation EU funds, facilitates the adoption of high-efficiency standards. Overall, the Passivhaus standard is establishing itself as a strategic tool for moving towards nearly zero-energy buildings, contributing to decarbonisation and urban sustainability, although it requires adaptation to the local climate to maximise its efficiency.

The implementation of RECONS certification demonstrates that voluntary sector-specific labels can drive specific sustainable practices in construction, particularly in responsible waste management. Cases such as the energy refurbishment in El Masnou and the company in Bages show that the separation and recovery of materials helps to reduce the carbon footprint, optimise treatment costs and improve corporate reputation. Academically, these results align with the literature on environmental certifications (BREEAM, LEED), which highlight the importance of transparency and recognition mechanisms in promoting the circular economy and preventing environmental impacts. Furthermore, the World Green Building Council (WorldGBC) exemplifies the importance of global cooperation in promoting sustainable construction practices, through the development and promotion of certifications such as LEED, the promotion of supportive government policies, and research into sustainable construction practices.

The results show that responsible waste management and the recycling of materials in construction help to reduce the carbon footprint and generate economic benefits. Energy Saving Certificates (CAE) prove to be an effective tool for incentivising energy efficiency and decarbonisation in buildings, whilst passive design and standards such as Passivhaus optimise energy consumption and indoor comfort. Finally, the voluntary RECONS certification reinforces the adoption of good environmental practices in SMEs, promoting waste separation, regulatory compliance and social recognition, thereby helping to consolidate a more sustainable and circular construction sector.

5. Conclusions

Based on the analysis of cases in the construction sector in Catalonia, it is concluded that the transition towards a more sustainable and decarbonised model is not only viable but is already underway thanks to the implementation of specific strategies in various areas.

Firstly, the recycling and reuse of construction materials are establishing themselves as fundamental pillars of the circular economy. These practices enable a significant reduction in the carbon footprint, a decrease in dependence on natural resources and the avoidance of waste generation. Furthermore, it is observed that their effectiveness does not depend solely on technology, but also on appropriate logistical reorganisation and coordination among the various sector stakeholders.

Secondly, Energy Saving Certificates (CAEs) are emerging as an effective tool for promoting energy efficiency. Their ability to monetise energy savings incentivises private investment in more efficient technologies, such as LED lighting, generating both economic and environmental benefits. On a global scale, these mechanisms help to correct inefficiencies in the energy market and advance decarbonisation targets.

Furthermore, the incorporation of passive design strategies and standards such as Passivhaus demonstrates significant potential for reducing the energy demand of buildings, even in Mediterranean climates. These solutions not only reduce energy consumption and emissions but also improve thermal comfort and indoor air quality, establishing themselves as a key pathway towards nearly zero-energy buildings.

Likewise, voluntary certifications such as RECONS demonstrate their ability to promote good environmental practices, particularly in waste management. These tools not only facilitate regulatory compliance but also enhance companies’ reputational value and promote greater transparency within the sector.

Overall, the results show that the combination of the circular economy, energy efficiency, design innovation and environmental certifications enables comprehensive progress towards more sustainable construction. However, to consolidate these advances, appropriate regulatory frameworks, technological innovation, stronger market incentives and training in these areas are required.

In short, the construction sector plays a vital role in the green transition, and the practices examined demonstrate that it is possible to reconcile environmental sustainability, economic viability and technical progress. A significant proportion of waste in Catalonia comes from the construction sector, and a considerable amount ends up in landfill, highlighting the need to move towards a more sustainable model. In this context, the use of recycled materials, such as recycled cement and aggregates, allows the technical quality of buildings to be maintained, reduces the extraction of natural resources and lowers the carbon footprint. Furthermore, Energy Saving Certificates (CAEs) and passive design improve the energy efficiency of buildings. And RECONS certification, together with specialised training and access to grants, reinforces the sustainability and competitiveness of companies in the sector.

The limitations of the study stem from potential selection bias, depending on the approach used to ensure the representativeness of the sector’s results. Regulatory and administrative barriers, as well as technical and economic constraints, also limit the ability to generalise these practices.

As for future lines of research, it is considered a priority to conduct a more in-depth quantitative analysis of the long-term environmental and economic impact of these measures and to expand the number of case studies. In addition to exploring sustainable materials and advanced recycling technologies, with logistics processes associated with the circular economy. Furthermore, strengthening the training and skills of sector stakeholders. Finally, further exploration of digital tools and life-cycle analysis represents a strategic approach to improving the sector’s efficiency, traceability and sustainability.