Re-Habiting the Rooftops in Ciutat Vella (Barcelona): Co-Designed Low-Cost Solutions for a Social, Technical and Environmental Improvement

Abstract

This research addresses urban inequality by focusing on the rehabilitation of communal rooftops in Ciutat Vella, Barcelona, the city’s historic district, where residential vulnerability is concentrated in a particularly dense heritage urban environment with a shortage of outdoor spaces. Using participatory methodologies, this research develops low-cost, removable, and recyclable prototypes aimed at improving social interaction, technical performance, and environmental conditions. The focus is on vulnerable populations, particularly the elderly. The approach integrates a bottom–up process and scalable solutions presented as a Toolkit of micro-projects. These micro-projects are designed to improve issues related to health, safety, durability, accessibility, energy savings, and acoustics. In addition, several possible material solutions for micro-projects are examined in terms of sustainability and cost. These plug-in interventions are designed for adaptability and replication throughout similar urban contexts and can significantly improve the quality of life for people, especially the elderly, in dense historic environments.

1. Introduction

This paper presents a comprehensive case study on the implementation of co-designed architectural prototypes for the adaptive reuse of communal rooftops in Ciutat Vella, the old district of Barcelona. These spaces, despite their potential, remain largely underutilized (Figure 1). Through participatory processes, this study developed removable, recyclable, and low-cost interventions to enhance habitability and community use of rooftops. This research led to the construction of two prototypes as example solutions for the recovery and re-use of the existing communal rooftops.

The health crisis resulting from COVID-19 amplified housing inequalities for the most vulnerable groups. In this context, the lack of adequate outdoor spaces [1] was exacerbated by the need to accommodate all domestic activities such as care, work, food or physical activities, indoors. Ciutat Vella was chosen as a case study because it was one of the districts with the highest incidence of positive cases per 100,000 inhabitants in Barcelona [2], among other reasons. Another significant factor was that this district, together with Nou Barris, Sant Martí, Sants-Montjuïc, Horta-Guinardó and Sant Andreu, has household incomes below the city average [3]. Alongside high rates of aging, social isolation, and poverty, Ciutat Vella also faces the pressures of gentrification and heritage protection constraints, which hinder affordable rehabilitation. In many historical centers, the processes of urban transformation act on the basis of their own logic compared to other neighborhoods [4], which consolidates a reality of specific characteristics in the economic and social division of space [5]. This situation involves a strong ambivalence historically expressed in the duality of centrality—degradation [6]. In Ciutat Vella district, many residents live in deficient living spaces, with insufficient surface areas, that are lacking in sanitation, ventilation and lighting [7], without quality outdoor and/or communal spaces. However, building rehabilitation costs tend to be higher due to the conditioning factors of heritage protection. At the same time, the district suffers from processes of gentrification because of the high pressure of tourism. These conditions are aggravated, for example, for the elderly, who, given the urban density conditions and characteristics of the district, such as the lack of accessible open-air living spaces, find it more difficult to fully integrate socially both with their neighbors and with the neighborhood’s services.

While this study centers on Ciutat Vella in Barcelona, similar initiatives across Southern Europe underscore the broader potential of rooftop rehabilitation as a tool for urban regeneration, especially in dense and ancient urban fabrics facing socio-environmental pressures. In Marseille (France), several community-driven projects have adapted underused rooftops in historic districts for urban gathering. These initiatives demonstrate how rooftop spaces can mitigate social isolation, particularly for elderly residents, and contribute to neighborhood resilience. Municipal programs have supported the transformation of school and public building rooftops into green, multifunctional areas. These interventions, particularly those led by associations such as “Les Toits Vivants” [8], focus on environmental education, biodiversity, and inclusive public space—all objectives shared with the present study’s emphasis on habitability, accessibility, and co-designed low-cost improvements. In Lisbon (Portugal), urban rehabilitation policies have begun to incorporate rooftop greening and communal use strategies in historical areas such as Alfama [9]. These efforts aim to counteract gentrification and heat island effects while fostering neighborhood identity and intergenerational interaction. These South European experiences affirm the rooftop as a key site for social innovation, particularly in historic urban districts. They demonstrate that participatory, low-cost, and reversible rooftop interventions can contribute significantly to improving urban sustainability, social inclusion, and public health—these being the driving principles.

The Ciutat Vella district presents an interesting case study, highlighting the shared problems of European cities and the rest of Barcelona’s districts, which face the growing challenge of an aging population [10,11] and socio-economic vulnerability. Ciutat Vella, paradoxically, has the lowest aging rate in the city (117.5 in 2019) for various reasons. However, the over-aging rate is 20% (2018), slightly above the average (19.2%), showing that there is a strong presence of people aged 85 and over. This district also has the lowest life expectancy and the highest percentage of people over 65 living alone, 32.8%, above the city average of 25.5% [12]. These indicators are complemented by a not entirely encouraging socio-economic picture of the district: Ciutat Vella’s disposable household income index (RFD) in 2019 was 84.3, below the 100 level for the city; 31.4% of the district’s resident population lives below the poverty line (2017), meaning that they live in a household with an income below 60% of the people’s average annual disposable income. It is worth noting that this rate is the second highest in the city, exceeding the Barcelona average by 11.8 points [12]. Moreover, it is also the district with the highest rate of severe material deprivation, at 11.2% in 2018, higher than the average of 6.5%.

From an architectural perspective, the district’s building stock is predominantly old, often in poor condition, and presents significant limitations in terms of accessibility, ventilation, and usable outdoor space. Flat rooftops are the most common constructive typology in Ciutat Vella and are typically communal, though they are rarely used or properly adapted for daily life [13].

The rooftops of buildings in Ciutat Vella have historically been conceived solely as a covering for the building; they are very often unused (Figure 1), with the exception of a few individual initiatives by residents. In some cases, they are for private use, but they are mostly for communal use by the residents of the building itself. Their physical and spatial conditions [13] make them a space of opportunity. Several authors point to rooftops [14,15,16,17] as a space for sociability and community building.

The use of roofs for community uses is not new, especially when the possible uses are productive [18] or touristic [19]. However, there is evidence of the benefit that its use can have for the living conditions of the elderly [20] and the potential that it can have at the level of recovery of green spaces [21] for the community as well [22,23,24,25,26,27].

These rooftops exist in a large percentage, with potential for transformation, particularly in buildings constructed before 1940. Their structural features, location within dense urban blocks, and current underutilization offer a unique opportunity to reimagine them as collective spaces that enhance community interaction and also improve individual living conditions. However, only a minority of these rooftops are currently adapted for communal use, despite their architectural potential. As such, they remain a significant resource for addressing spatial inequalities, particularly for elderly residents, through low-cost rehabilitation interventions. Therefore, Barcelona’s Mediterranean climate and its physical conditions can create the conditions so that, with small interventions, roofs can become an intermediate space between domestic and community environments in the public space, facilitating social inclusion in general [28]. And, given the aforementioned particularly unfavorable conditions of the older population in Ciutat Vella, they can contribute to active aging, physical and mental health, and personal and collective well-being [29].

The prototyping process presented in this research seeks, broadly and through participatory processes, to identify the most appropriate uses for improving the living conditions of the elderly in Ciutat Vella.

Also, the resultant solutions have to be possible to be executed collaboratively, at an affordable cost, and using methods of dry construction and reusable systems. In this sense, the aim is to value the capacity of the small scale in the architectural intervention, exploring the limits of uncomplicated constructive proposals but with a high impact on the quality of life of the communities. One of the main objectives of the proposal is that the elements of the prototypes can be self-managed, built and replicated by the communities in the short and the long term.

In short, as the characterization study concludes [13], we find a scenario with a very old and degraded building stock, occupied by elderly people, many of them women who live alone and often at the threshold of poverty and residential exclusion. These prototypes aim to help to respond to the needs of the population, with a housing structure that does not meet the minimum conditions required and at the same time has a high historical value that sometimes increases costs and hinders the process of rehabilitation.

2. Aims and Scope of the Research

This article shows the methodology and co-designed solutions proposed for the recovery of the communal rooftops in Ciutat Vella district. The innovation of the proposal lies in the potential for transformation with low-cost solutions that these rooftops have, and also in the capacity of the residents and the neighborhood care networks to reconquer the right to decent housing in the city, improving their living conditions from an environmental, social and economic point of view by themselves. These solutions are based on a process of social transformation and must therefore be accompanied by social and technical improvements that make it possible for residents to interact with each other in these unused spaces.

This study aims to reimagine underutilized rooftop spaces as vital community infrastructures, with a specific focus on the Ciutat Vella district. The primary objectives are fourfold: (1) to identify both technical and social needs through participatory methods; (2) to design simple, cost-effective, modular elements that can be easily assembled on rooftops; (3) to foster healthy habits and enhance social cohesion; and (4) to support the community-led use, maintenance, and transformation of rooftop spaces.

These objectives are grounded in the specific socio-spatial conditions of Ciutat Vella and seek to empower local residents to improve their living environments. Through localized design and collaborative engagement, this study provides a replicable framework for urban regeneration that is environmentally sustainable, economically viable, and socially inclusive.

This article is structured as follows: Section 3, the Methodology section, presents the methodological steps of the research leading to the definition of microprojects; Section 4 focuses on identifying opportunities using the co-design process and offers a definition of the different solutions; Section 5 focuses on the technical aspects of the different solutions and analyzes the different material options in terms of sustainability and cost effectiveness; and finally, Section 6, the Conclusions, summarizes the main contributions of the article.

3. Methodology

The methodology employs an interdisciplinary and mixed-methods approach to develop the micro-projects. It combines quantitative and qualitative research, including demographic analysis, field surveys, participatory design workshops, and GIS-based mapping.

The process is structured into four key phases (Figure 2):

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Phase 1: Typological and sociological characterization of the rooftops in the district;

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Phase 2: Identification of user needs through community roundtables and stakeholder interviews;

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Phase 3: Design and prototyping of interventions addressing environmental, structural, and social dimensions;

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Phase 4: Real-scale implementation and evaluation of two selected prototypes.

Figure 2. Methodological outline of the proposal.

Figure 2. Methodological outline of the proposal.

The proposals developed were based on the capacities and opportunities present in the neighborhood (available spaces, urban and architectural morphology, similar proposals and interventions that neighbors had already proposed or carried out, or local products and services), and were focused on the problems of the neighborhood expressed in 3 areas:

• HABITABILITY: Improvements in the dimensions, surfaces and materials of the space to intervene in, as well as in the conditions of sunlight, shade and comfort.
• SAFETY: Improvements in the prevention of health risks and fire hazards (installations and antennas, flammable material, unstable elements, etc.); simple improvements to reduce the stigma and perception of insecurity in the building itself, avoiding dark and hidden corners through measures such as the installation of mirrors and the search for greater transparency in enclosures.
• SUSTAINABILITY: Improvements in energy efficiency and comfort in outdoor spaces, seeking the maximum impact on comfort in indoor spaces as well as environmental improvement beyond the staircase of the building, and, on the other hand, seeking an improvement in social sustainability, promoting spaces for coexistence, and establishing solidarity networks and social relations. To achieve these specific objectives, this research took all the roofs of the residential buildings in the district as a sample. A toolkit of micro-projects was drawn up to improve the conditions of use, activity and comfort on the terraces, and two full-scale prototypes of the improvement solutions were co-designed and implemented in order to validate their effectiveness.

To identify and select the case studies within the Ciutat Vella district, a comprehensive mapping and characterization process was undertaken using a combination of open-access municipal data, GIS analysis, and on-site inspections. The primary data sources included cadastral maps, building typology inventories, and demographic indicators provided by the Barcelona City Council (Ajuntament de Barcelona) and the Statistical Institute of Catalonia (IDESCAT). Fieldwork was then conducted to verify the physical conditions and accessibility of rooftops. All selected rooftops are part of multi-family residential buildings and are technically private spaces with communal access, meaning they are owned collectively by the building’s residents. This distinction is critical, as it implies that any proposed interventions—such as the co-designed prototypes—must be approved and managed by the residents themselves, potentially with the support of local associations or cooperatives. The participatory methodology was thus adapted to engage directly with residents and local stakeholders, recognizing their legal and social role as stewards of these semi-private communal spaces.

This methodological framework emphasizes participatory co-creation and aims to ensure that outcomes are tailored to local conditions and community aspirations. The prototypes are assessed not only for technical viability but also for their potential to catalyze sustainable social transformation.

4. Co-Design Process

The co-design phase started with a comprehensive rooftop inventory and assessment to understand existing uses, physical constraints, and community practices. This was followed by workshops and roundtables involving residents, local organizations, and technical experts. Together, they identified priorities and collaboratively developed design solutions.

4.1. Diagnosis and Definition of the Areas of Action as Prototypes (Phase 1)

Quantitative information was compiled on the basis of primary data and previous analyses, which provide proven knowledge of the housing, construction and technical characteristics of the building and roof spaces in the district, as well as the socio-demographic and socio-economic characteristics of the resident population.

In order to draw up the socio-demographic profile and the living conditions of the population of Ciutat Vella, secondary quantitative data from the Department of Statistics of Barcelona City Council and the Statistical Institute of Catalonia were also used. In addition to this first phase, the working team identified the key actors in the areas of action with the support of the Oasi Urbà [30] association of the Raval neighborhood.

This first phase generated a characterization database of all the roofed spaces in the Ciutat Vella district, allowing the selection of 13 case studies spread over different neighborhoods in the district (Figure 3). These had different typological characteristics and were in different states of conservation, providing the prior technical information [13] that was needed to address the subsequent prototyping.

In the first phase, the most common elements that were already implemented on rooftops by the neighbors were defined, and a first generic outline of their possible formalization as a prototype design was made. A catalog of modular elements—such as pergolas, planters, raised platforms, and vertical partitions—was created to offer adaptable and scalable design options (

Table 1. Prototyping elements.

Element A	Scheme A	Element B	Scheme B
Gazebo		Clothesline
Wall		Greenhouse
Platform		Cupboard
Planter		Handrail

Drawings by REARQ.

). Each element was evaluated for regulatory compliance, safety, ease of use, and sustainability. The process culminated in eight case studies that reflect the diversity of architectural typologies and demographic needs across the district.

At the same time, a technical inspection was carried out on the 13 selected case studies [13], which showed that there was potential for using the Ciutat Vella roofs, and a series of possible technical improvements to be made were identified. The technical improvements identified included the following (as also shown in Table 2):

• Health: Improvements in the dimensions and surfaces where the intervention is to take place, providing a horizontal plane as a floor for the activity; improvements in existing materials, through the removal of toxic materials; improvements in sunlight, shade, and comfort conditions, providing shade elements to ensure comfort in the summer; and finally, promoting prototype uses regarding healthy habits, plant and vegetable gardening, and community activities.
• Safety: Improvements in health and fire risk prevention by removing obsolete installations and antennas, flammable materials, unstable elements, etc.; improvements in fall protection for perimeter railings, which are often lower than current regulations require, by using taller elements in the prototype or installing planters to prevent falls; and, finally, simple improvements to reduce the stigma and perception of insecurity in the building itself, avoiding dark and hidden corners through measures such as installing mirrors and seeking greater transparency in enclosures.
• Durability: Improvements in the durability of the original roof layers thanks to the protection provided by the prototype floor, which also allows water to filter through without interfering with the proper functioning of the roof; providing a use and maintenance manual of the prototype for the community, for its greater durability; and, finally, providing greater flexibility and versatility to gender-sensitive spaces, with the main objective of caring for and promoting healthy usage habits.
• Accessibility: Improvements to adapt spaces to all people and all life stages, with an emphasis on accessibility and safe use, taking into account the need for a flat platform for activities with easy access via low-slope ramps, and the ergonomics of the various planters, clotheslines, seatings, etc.; attention is also paid to the temporary management of compatible uses that promote coexistence and inclusion.
• Energy saving: Improvements in the energy efficiency and comfort of outdoor spaces by providing naturally ventilated spaces with movable sunshade elements that can be moved according to need and season; seeking maximum impact on comfort in interior spaces by creating a ventilated chamber beneath the prototype platform that improves the climatic conditions of roofs, which often lack thermal insulation. This chamber provides special protection from solar radiation, which, in summer, in Mediterranean climates and on uninsulated roofs, has a very negative impact on the comfort of upper-floor homes. Thus, the installation of the prototypes has the potential to reduce energy consumption for air conditioning. Other improvements include installing clotheslines, which would reduce energy use through the use of dryers, and finally, seeking to improve social sustainability by promoting spaces for coexistence, for the establishment of solidarity networks, and to promote social relationships.
• Noise: Improvements in the perception of exterior noise from the interior thanks to the chamber generated by the prototype floor relative to the original roof and the design of the prototype’s elastic contact with the building; potential improvements in noise generation by promoting civic activities linked to the prototype’s use.

Table 2. Technical improvements (according to Spanish regulations [31]).

	Floor	Elements	Supply Systems
Current status	>10% Floor slope	No common elements	Obsolete supplying systems
Accessibility	Removing steps	Covered flatness
Security of use	Safe use	Cleaning storage	Energy point
Health	Adding ventilation	Daily care
Durability/ Structure	Covered protection	Sun protection	Water evacuation
Noise protection	Adding insulation (noise)	Noise protection	Water evacuation
Energy saving	Adding insulation (thermal)	Thermal protection	Water evacuation

Drawings by REARQ.

Table 2. Technical improvements (according to Spanish regulations [31]).

	Floor	Elements	Supply Systems
Current status	>10% Floor slope	No common elements	Obsolete supplying systems
Accessibility	Removing steps	Covered flatness
Security of use	Safe use	Cleaning storage	Energy point
Health	Adding ventilation	Daily care
Durability/ Structure	Covered protection	Sun protection	Water evacuation
Noise protection	Adding insulation (noise)	Noise protection	Water evacuation
Energy saving	Adding insulation (thermal)	Thermal protection	Water evacuation

Drawings by REARQ.

4.2. Identification and Definition of Needs (Phase 2)

Once the first phase of characterization and diagnosis was completed, the second phase of detection and definition of the actual deficiencies and shortcomings, as well as of the roofs’ potential to cover these needs, was carried out.

Through participatory workshops and roundtables with residents, neighborhood associations, and local professionals, key community needs were identified. These sessions highlighted deficits in rooftop accessibility, safety, comfort, and usability. Participants emphasized the lack of shaded areas, secure boundaries, and spaces for social interaction or care activities. Based on this input, a catalog of collective needs was created, organized into thematic activities: care, food, and physical activity (

Table 3. Collective or individual activities for communal rooftop spaces.

	To Care Collectively	To Eat Collectively	To Participate in Sport Collectively
Scheme Collective use	Rest	Eating	Climbing
Scheme Collective use	Kids	Horticulture	Ball play
Scheme Collective use	Reading	Non-seasonal Horticulture	Exercise
Scheme Collective use	Contemplation	Food storage	Meditation
Scheme Collective use	Assembly	Food preparation	Activities
Scheme Collective use	Collective laundry	Celebration	Relaxation
Scheme Collective use	Collective clothes drying	Biodiversity	Kids’ activities

Drawings by REARQ.

). This phase ensured that design proposals would directly reflect the lived experiences and priorities of rooftop users for individual or collective activities in communal spaces.

This phase was combined with inspections and technical assessments of the roofs.

The participatory process was previously conducted and published [32,33,34] and involved several roundtable discussions and interview groups in each neighborhood, facilitated by the Oasi Urbà association, linked to the social fabric of Ciutat Vella, and with the participation of a sociology team from the University of Barcelona.

From the surveys conducted among the residents of the district, it was found that community rooftops have multifold potential for community use. This potential includes the following: (1) serving as a meeting space for the community’s residents; (2) serving as a place for engaging in enjoyable activities that bring personal satisfaction and well-being, i.e., breathing, looking, and having a view; (3) fostering greater environmental sustainability through the care of the garden and plants; and (4) being a place of sociability, both within and between neighborhood communities, providing space for conversations, chats, and celebrations, such as barbecues, birthday parties, street parties, etc., which contribute to creating or reinforcing a sense of community, in line with previous works [14].

Common needs identified included accessible and safe walking surfaces, shaded areas for rest and socialization, dedicated zones for gardening or drying clothes, and storage for communal tools or personal belongings. These needs were then translated into design features integrated into the prototype catalog.

According to the testimonies of neighborhood communities in Ciutat Vella [29], the communal use of the rooftop requires a series of conditions, such as the following: on the one hand, technical improvements to the space (accessibility, comfort, safety, and durability), and, on the other hand, improvements in collective uses, which involve the drafting and enforcement of a map of uses and regulations.

4.3. Elaboration of Design Proposals (Phase 3)

With the aim of elaborating a Toolkit of micro-projects for the implementation of improvements in collective roofed spaces, each of the cases characterized in the district containing typological diversity and deficiencies was taken, and a co-design process was initiated. This co-design process was based on working groups made up of research architects, specialists, and key actors in the district:

• Organization of working groups comprising researchers and specialists in each field (sociology and architecture), residents and neighbors of the neighborhood, organizations and members of the associative fabric, companies, and local professionals in the sector.
• Development of collective work sessions for the definition of needs by combining the possible elements.
• For each of the elements, definition of their potential implementation by self-building or with the help of local installers.

The co-designed solutions were implemented on a real scale and were shown to the public in the form of an exhibition from Autumn 2023. In this phase, the evaluation of the impacts and the efficiency of the solutions involved the prospection and technical analysis of the built solutions, as well as the study of the assessments by and perceptions of the resident population.

Located in Raval Sud, both case studies highlight rooftops from distinct architectural periods and social compositions, notably with a high concentration of elderly residents.

Case Study 1 (Figure 4) features a large rooftop that allows for a wide range of interventions. The prototype here focuses on enhancing safety, accessibility, and hygiene by improving stairwell ventilation and repairing structural issues. Key additions include a floating platform for better access and insulation, especially for the top floor, and elements that support collective dining.

Case Study 2 (Figure 4) has a smaller rooftop, requiring selective implementation. Similarly to Case 1, the focus is on safety, accessibility, and hygiene, with stairwell ventilation and crack repairs. The proposal includes a floating platform for access and insulation, plus a pergola and planters to encourage food-related and communal activities.

Located in Raval Nord, these cases involve rooftops within a block defined by housing units smaller than the district average, making them ideal for targeted rooftop improvements. Both rooftops are compact, requiring a selective approach to interventions. In each case, the prototypes focus on resolving key technical issues, including safety, accessibility, hygiene, energy efficiency, durability, and noise reduction.

In Case Study 3 (Figure 5), the proposal includes a floating platform to enhance accessibility, along with a pergola and planters to encourage food-related and physical activities. Case Study 4 (Figure 5) follows a similar approach but introduces a multifunctional vertical element for varied uses, along with planters to foster biodiversity.

Situated in a block with a high proportion of elderly residents and diverse building types, these case studies reflect the area’s architectural variety and aging population.

In Case Study 5 (Figure 6), a relatively modern building with a spacious rooftop allows for interventions focused mainly on expanding uses rather than addressing technical issues. The proposal includes a pergola with a vertical element for multiple activities and formalizes the presence of existing clotheslines.

Case Study 6 (Figure 6) involves a medium-sized corner rooftop exposed to two façades, requiring careful planning. The prototype addresses safety, accessibility, hygiene, energy efficiency, durability, and noise reduction. It includes a floating platform for access, a vertical storage unit, and a new parapet to ensure safe use.

Case Study 7 (Figure 7), in La Barceloneta, is located in a block with a high proportion of elderly residents and diverse building types. The rooftop is small and highly exposed on three sides, limiting the range of possible interventions. Despite these constraints, the prototype addresses key technical issues such as safety, accessibility, hygiene, energy efficiency, durability, and noise protection. The proposed improvements include a floating platform for accessibility and a new parapet to ensure safe use.

Case Study 8 (Figure 7), in the Gothic Quarter, also features a high percentage of older residents and architectural diversity. The larger rooftop allows for broader interventions. Given the building’s age, the prototype focuses on resolving technical deficiencies, including accessibility, insulation, and noise control. A floating platform is proposed along with added thermal and acoustic layers. The design also incorporates elements to support collective dining activities.

The eight rooftop interventions across Ciutat Vella—Raval Sud, Raval Nord, Sant Pere i Santa Caterina, La Barceloneta, and the Gothic Quarter—demonstrate how co-designed, low-cost architectural solutions can address diverse socio-technical needs while fostering community use of underutilized spaces. All selected rooftops reflect the district’s common challenges: aging populations, poor building conditions, and limited access to outdoor communal spaces.

Case Studies 1, 5, and 8 stand out for their generous rooftop dimensions, allowing broader interventions. These prototypes emphasize improved technical performance (e.g., thermal and acoustic insulation), while also enabling social activities, like collective dining, or multipurpose use through pergolas, vertical structures, and the reorganization of informal practices (like clotheslines).

In contrast, Cases 2, 3, 4, 6, and 7 face constraints due to rooftop size or exposure, requiring more selective and compact solutions. Despite the limitations, these cases incorporate critical upgrades such as horizontal floating platforms for accessibility, noise protection, and lightweight add-ons like planters or vertical partitions. They also address safety, hygiene, and ventilation needs—key issues identified through participatory diagnostics.

The rooftops span different historical periods. Older buildings (Cases 1, 3, 4, and 8) demanded more technical remediation, while newer ones (Case 5) allowed a shift in focus toward expanding functionality. Some rooftops (e.g., Case 7 in Barceloneta) were also highly exposed, limiting the use of overhead structures. Despite their diversity, all cases align with the project’s strategic pillars: improving accessibility, habitability, safety, environmental efficiency, and social sustainability. The modular, removable prototypes were tailored through participatory workshops and roundtables, using a catalog of elements (Table 1) adaptable to each rooftop’s specific constraints and community aspirations.

This cross-case analysis affirms that even minimal, low-cost interventions, when context-sensitive and co-designed, can significantly transform rooftops into inclusive, safe, and multifunctional community spaces, especially for vulnerable groups such as the elderly.

4.4. Implementation and Evaluation of Prototypes (Phase 4)

Two full-scale prototypes were implemented (Cases 2 and 5) to validate the designs under real-life use. These rooftop interventions addressed the deficiencies identified earlier through elements like floating platforms, pergolas, and vertical structures. Residents confirmed improvements in accessibility, comfort, and perceived safety. The process demonstrated that co-designed, small-scale interventions can generate high-impact results when aligned with local needs and supported by participatory governance. Drawing on the outcomes of the research, a Toolkit of modular design elements was co-developed and two prototypes were implemented. These included pergolas, planters, platforms, storage units, handrails, and clotheslines—designed to be low-cost, removable, and adaptable. Each element was evaluated in terms of technical feasibility, regulatory compliance, environmental performance (via LCA), and user value. The modularity of the designs allowed them to be tailored to varying rooftop sizes and conditions. Eight rooftops were selected for specific prototype development, and two of them were built, balancing both the potential for transformation and the ability to test a wide range of interventions under real conditions.

5. Introduction to Economic and Sustainability Parameters

The proposal focuses on a comparative study of three distinct materials, namely heat-sealed bamboo, copper-treated pinewood, and galvanized steel profiles. The main objective is to assess their environmental impact through Life Cycle Analysis (LCA).

LCA allows for the obtention of various indicators of the environmental impact of a process or product. In this case, two are primarily considered, resource consumption (kg) and greenhouse gas emissions (GWP-GHG), given the current climate emergency. The Global Warming Potential indicator excludes biogenic carbon (GWP-GHG according to Intergovernmental Panel on Climate Change IPCC 2013 GWP 100a). This indicator includes all greenhouse gases included in GWP-total, but excludes biogenic carbon dioxide uptake and emissions as well as biogenic carbon stored in the product. Its permit indicator creates comparability with climate declarations and carbon footprints according to ISO 14067 [14].

The LCA methodology includes 4 main stages (A, B, C, and D) and 17 substages. Stages A1–A5 address the extraction, transportation, transformation, and construction of a building. Stages B1–B7 address the building’s operational capacity, in terms of both use and durability, and maintenance. Stages C1–C4 provide information on the end of its life, its deconstruction, and the final disposal of waste, while Stage D provides information on the reuse, recovery, and recycling potential of the products.

In this case, a cradle-to-gate LCA with modules C1–C4 and module D is considered. Following the recommendations of UNE-EN 15804:2012+A2:2019 [34] whenever products containing biogenic carbon are considered, we cannot omit the declaration of modules C1–C4 and module D, these being the minimum phases required for an EPD (environmental product declaration).

Table 4. (GWP-GHG according to IPCC 2013 GWP 100a). Global Warming Potential excluding biogenic carbon. “Cradle to gate with modules C1–C4 and module D”. UNE-EN 15804:2012+A2.

	CODE	Material	EPD Ref.	Declared Unit	Product Stage	End of Life Stage				Potential Resource Recovery
					A1–A3	C1	C2	C3	C4	D
	Timber	Copper-treated pinewood	S-P-08618	1 m3	5.68 × 101	8.44 × 10−3	1.29 × 10	4.70 × 10	1.53 × 10	−6.32 × 101
	Bamboo	Heat-sealed bamboo	S-P-01925	1 m3	8.52 × 10−1	0.00 × 10	2.29 × 10−2	0.00 × 10	3.10 × 10−3	−7.44 × 10−1
	Steel	Galvanized steel profiles	S-P-09494	1 Ton	1.71 × 103	6.27 × 101	8.55 × 101	2.27 × 101	0.00 × 10	−9.92 × 102

shows the values considered for the LCA calculation according to the three main materials.

To facilitate the evaluation, a comparative table is constructed for each project element, outlining the potential LCA for the different materials. This comprehensive analysis aims to provide a holistic understanding of the ecological footprint of each material choice, allowing for an informed decision-making process.

The underlying goal of this project is to contribute to the creation of a truly sustainable built environment. One of the key principles guiding this endeavor is the concept of the circular economy. In essence, this involves reusing products and recycling materials from current construction practices to serve as valuable resources for future projects, understanding the building as a “materials bank”. By adopting this approach, the project seeks construction solutions that are easy to assemble and disassemble, with lightweight bolted joints, allowing for the construction of buildings with capacity for more people and minimizing the total consumption of materials.

Furthermore, a crucial aspect of this sustainable vision involves proactive planning for the recycling of all building materials. By considering the end-of-life stage of materials right from the design phase, the project aims to establish a closed-loop system where materials can be efficiently recovered and repurposed. This approach not only reduces waste but also decreases the reliance on extracting new resources, thereby lessening the strain on the environment.

In alignment with the urgent need to address climate change, the project also emphasizes the immediate cessation of all greenhouse gas emissions. Recognizing the significant role that the construction industry plays in carbon emissions, adopting low-carbon materials and implementing energy-efficient processes are paramount. By prioritizing sustainable materials with lower embodied carbon, such as the evaluated heat-sealed bamboo and copper-treated pinewood, the project aims to mitigate the environmental impact associated with construction and contribute to the global effort of combating climate change.

In summary, the project’s comparative study of heat-sealed bamboo, copper-treated pinewood, and galvanized steel profiles through Life Cycle Analysis provides valuable insights into their environmental footprints. By striving for a circular economy, planning for material recycling, and aiming to reduce greenhouse gas emissions, the project aims to pave the way for a sustainable built environment that prioritizes the efficient use of resources while minimizing its environmental impact.

The results of the LCA for the “cradle-to-gate” type with modules C1–C4 and module D are presented in

Table 5. LCA results.

Scheme	Element	Functional Unit	LCA Results
	Gazebo	Square meter
	Clothesline	Square meter
	Wall	Linear meter
	Greenhouse	Unit
	Platform	Square meter
	Cupboard	Linear meter
	Planter	Unit
	Handrail	Linear meter

. This comparative analysis considered the different alternatives with the three main materials. The resulting values are shown according to the characteristic functional unit of each element, which can be square meters, linear meters, or per unit.

Overall, it is observed that the wood- and bamboo-based solutions are lighter than the steel ones, except for the Gazebo element. Given the geometry and structural requirements, this solution best optimizes the structure’s dead weight. Furthermore, the global warming potential (GWP) indicator shows that wood- and bamboo-based solutions are low in embodied CO2e, while steel-based solutions can have an impact up to 15 times greater than the former.

Although wood and bamboo solutions are environmentally competitive, we cannot ignore the fact that the use and cultivation of bamboo in Europe is very limited, and wood is a widely available material. It should be noted that for low-environmental-impact materials, transportation (Stage A4) can have a significant impact on the overall impact, making international imports pointless.

In this case, wood-based solutions are the most appropriate for a project of this type, where proximity and self-construction will be essential, not only for environmental sustainability, but also for economic and social sustainability.

Figure 8 shows the results shared based on the economic aspects calculated using the direct costs from the local BEDEC 2025 database [35], where galvanized steel-based solutions are more advantageous in the vast majority of elements and prototypes. These values are between 12% and 60% cheaper than wood or bamboo. This means that in most projects, steel will be the solution of choice unless environmental aspects are prioritized. On the other hand, only in the “Wall” and “Handrail” elements are the costs of steel higher, due to the large amount of material they use. Bamboo-based solutions are more expensive than wood-based solutions, as this material does not have a sufficiently extensive planting and marketing network in Europe. This means that the economic costs of importing it are not affordable for most projects.

Steel is a well-established material in the construction sector with an economically optimized industry. This makes it the most competitive solution in most cases. In contrast, bamboo cannot currently be considered a common material in European construction, where there is no solid production base or distribution network. In this context, wood offers an interesting balance between economic and environmental costs, making it the most suitable solution.

In terms of maintenance, both wood and bamboo exposed to the elements are less durable than galvanized steel. However, given the temporary nature and flexibility of these roofing elements, maintenance issues become less important. Therefore, with all these aspects evaluated, wood offers a better balance between economic and environmental costs throughout its useful life.

6. Conclusions

This project foresees the manufacture of full-scale, dismountable and recyclable prototypes to be exhibited and verified by the public, applicable to different types of roofs, according to different uses and possible management models.

This project also contemplates the methodology as a result in itself, due to its capacity to empower the elderly, the resident carers and the associative network, with a view to achieving the transformation, improvement and management of the community residential space of the rooftops, as well as to establishing stable networks of collaboration between the local associative network, the residents, and the scientific and technical research and innovation developed by the public university. The expected results can provide methodological and technological tools to improve the living conditions of the elderly and the people around them in communities and housing in the most disadvantaged areas, thus helping to strengthen urban resilience in the face of crisis and emergency situations, and to improve sustainability in its environmental, economic and social aspects.

The main differential element of the solutions to be designed and implemented with respect to standard solutions in the six specific areas described are the requirements for dry construction, the requirement to use recyclable materials that can be dismantled, and the requirement to use low-cost construction systems, in workshop prefabrication, or simple manufacturing that facilitates their implementation and maintenance in the medium and long term. In this sense, solutions based on copper-treated pinewood maintain the best balance between technological, economic and environmental requirements, based on the proximity and self-management of resources.

Most of the solutions must be able to be implemented without planning permission, so that residents can manage them themselves with the necessary technical support and accompaniment. The new digital tools we use at the university offer solutions that can be very efficient and affordable, allowing for a great deal of specificity in prefabrication and simple and safe self-construction. The efficiency of the micro-projects will be measured according to their capacity to simultaneously resolve one or more areas, and their potential impacts in relation to the cost and difficulty of implementation. To this end, the Microproject Catalogue will incorporate an assessment of the costs and a description of the implementation processes and requirements. Likewise, the replicability of the solutions to be proposed will be translated into the need to design universal interventions, with a certain degree of autonomy, flexibility and adaptability to the material and spatial characteristics of other rooftops where they can be replicated.

Another innovative aspect of the project with respect to other interventions on Barcelona’s rooftops lies in the development, during the needs detection phase, of local and transversal working groups that integrate researchers and specialists, professionals from the care, health, housing and rehabilitation sectors (public administration), as well as from associations and the resident population, in such a way that both future designs and prototypes can integrate the collective and transversal capacity of multiple agents and people with first-hand knowledge of the problems and needs of the neighborhood, the difficulties and opportunities for management and maintenance, and the quality and efficiency standards of the solutions to be designed and applied specifically in Ciutat Vella. This is a process that should not only allow for the consolidation of collaboration networks but should also encourage the professionalization and training of residents, associations, public administration professionals and other local groups interested in technical–architectural and relational issues, in the habits of the use and management of processes of reappropriation, transformation, management and maintenance of community spaces, as well as in innovative techniques and materials that are increasingly in demand (bio-construction, dry construction, industrial design with recycled materials, etc.). The use and application of materials or systems that are already part of the local productive fabric (such as certain types of fabrics applicable to solar protection systems, thermal insulation, or furniture and finishes, among others) will also be promoted, guaranteeing that they do not pose a risk in the event of fire, in order to boost their commercialization and scalability or improve their technological efficiency and applicability.

The prototyping of some of the micro-projects contained in the catalog applied to real pilot cases guarantees a level of technological maturity higher than that of TRL6 [36]. The project is based on bottom–up design and the prototyping of ad hoc solutions, despite these being constructed in a non-finalist environment (transferable and for exhibition). This allows for the criticism and evaluation of the perception of older people in the district, of the associative fabric and of the interested population in general, thanks to the possibility of observing the real solutions applied and exhibited in different contexts.