In common perception, the extent of the architectural discipline often terminates at the act of designing buildings. This seemingly linear act, however, shapes the ways we build, inhabit and share spaces, and the ways we think about each, is far from linear. Is it time to rethink traditional built environments? Who gets a say, and what should the future of architecture stand for? These questions lie at the centre of Bellastock’s creative pursuits. The Paris-based cooperative has, since its inception in 2006, treated architecture as a process of experimentation, collaboration and transformation. The French architects embrace construction as a cyclical practice where materials, people and ideas coalesce. Through their work in education, research and professional practice, they reimagine architecture as a collective endeavour rooted in participation and reuse.

Driven by a belief that sustainability is as much a cultural shift as it is a technical challenge, Bellastock’s projects—ranging from temporary urban interventions to explorations in reuse and transitional urban planning—foreground agency, imagination and care. Their mission transcends merely designing objects to facilitating processes that empower communities, shift mindsets and contrive new ways of making the built environment. In a conversation with STIR, Esther Rejai, head of communications at Bellastock and Hugo Topalov, reuse and circular economy project coordinator, reflect on the origins of the cooperative, their evolving methodologies and the role of experimentation in shaping a more ecological and democratic architectural practice. Edited excerpts of the conversation follow.

Anushka Sharma: Could you tell us about the inception of Bellastock? What sparked the idea of founding a cooperative centred around experimental architecture?

Esther Rejai: Bellastock is an annual event that began in 2006 at ENSA Paris-Belleville. Created by and for students, it responds to the observation that architectural education is disconnected from reality, particularly from construction sites and materials. Organised without teachers and outside the school walls, this event brings together a significant number of participants (between 200 and 1,000) and a limited amount of material resources for a collective experiment: of building and inhabiting a temporary city, before deconstructing it to restore the site to its original state, all in four days. Each edition explores a specific theme: construction techniques (inflatable, earth, straw), urban scenarios (floating, suspended, mobile cities) or concepts (waste, living, conviviality).

Repeated over the years, this architecture festival has gradually taken shape to meet the growing interest of students and institutional recognition, becoming a national reference in the field of what is now known as ‘experiential learning’. The festival became an association in 2010. One of the editions of this festival, titled Le Grand Détournement (2012), focused on building with objects that are considered as waste. For Bellastock, this was the first step towards reuse and the beginning of numerous experiments and research projects.

In 2019, Bellastock wanted to take a new step forward by mobilising more people around common objectives in architecture, regenerating imaginations and practices, defending transdisciplinarity and promoting more horizontal models of governance at work. Bellastock officially became a Social and Solidarity Economy structure and the only Cooperative Society of Collective Interest in Architecture (SCIC) in France. In 2025 – 26, Bellastock will enter a new phase as we officially open our architecture agency.

Anushka: Bellastock is known for its pioneering work with reuse and circular design. How did the focus on using salvaged materials evolve, and what challenges did you face in integrating them into architectural practice?

Hugo Topalov: Bellastock began working on reuse in 2006, at a time when few people were interested in the subject. Twenty years later, the regulatory, political and societal context has evolved and is increasingly favourable to reuse. As a result, demand is growing and becoming more structured. While a few years ago Bellastock's main effort was to convince and persuade people of the benefits of reuse, it is now more a question of implementing it in an operational and widespread manner. Nevertheless, there are many obstacles that remain: technical, economic, insurance-related, organisational and, above all, cultural. Finally, educational work is always necessary, as not all stakeholders are at the same level of acculturation.

Anushka: Your mission emphasises “more global reflection on transitional urban planning”. What gaps in traditional urban planning does your practice identify and aim to address?

Hugo: Urban planning projects often take a long time. This highlights the importance of considering the temporary use of unoccupied spaces (brownfield sites, vacant lots, vacant premises, etc.). These spaces can be used to host festive events, temporarily enliven public spaces and experiment with new uses and activities with future residents, generally on a short-term basis. Bellastock's position is that this temporary occupation should also serve to have a real impact on future urban or real estate planning, helping to respond more appropriately to local needs. In conclusion, contrary to what its name suggests, transitional urban planning is only of real interest if it has a lasting effect on future neighbourhoods.

We want to move away from the architect's position as the sole expert on a project and give a voice to the various stakeholders: residents, artisans, local authorities, etc., to help find the best solution—one that will have the least impact on material and immaterial resources. – Esther Rejai, Bellastock

Anushka: Your approach blends artistic experimentation with architectural research. How do you balance creative freedom with constraints—such as structural, regulatory, or financial—in your projects?

Hugo: Firstly, what may initially appear to be a constraint can prove to be a driving force for architectural creation. For example, using existing materials to construct a building offers almost infinite possibilities for creativity in inventing new architectural aesthetics. It is therefore not a constraint, but an asset, if we are open to changing our habits in the way we design, but also in the way we perceive architecture (after all, art invites us to change our perceptions of our daily environment). In line with this logic, we are working hard every day to demonstrate that reused architecture is feasible in economic, technical and regulatory terms. In the longer term, the objective is, of course, to change the structural framework; we are participating in discussions on draft legislation in this regard.

Anushka: Can you walk us through your methodology—from ideation to construction—especially in temporary or self-built environments like the annual Bellastock festival?

Esther: Thinking of the Bellastock festival as an educational tool in architecture is far from easy. Indeed, it does not fit into the usual framework of objectives for acquiring knowledge or skills. The ephemeral, often makeshift nature of the projects makes it difficult to demonstrate the construction skills acquired by the participants. Characterising the specificities of this pedagogy involves questioning the methods rather than the content. The event-driven and ephemeral nature of this approach leads us to prioritise the process over the quality of the constructed object. The conditions for success in this exercise lie in its ability to connect the resources of a place, constructed objects and common uses. The combination of designing, building and inhabiting makes it seem like a practice of architectural permanence, but one that is inscribed in an extremely condensed temporality and with a very large number of participants (up to 1,000).

We propose four complementary approaches to characterise the learning methods deployed throughout the festival:

• Experiential pedagogy: being active in order to learn by doing.
• Situational pedagogy: increasing experiential learning through connection to reality.
• Cooperative pedagogy: developing collective intelligence and cooperation.
• Self-generative pedagogy: encouraging improvisation, a bottom-up approach rather than a top-down one.

In contrast to a techno-solutionist view of sustainability, we propose frugal and low-tech approaches to architecture that place ecological, social and cultural issues on an equal footing. – Hugo Topalov, Bellastock

Anushka: How do you engage with communities, students and other stakeholders during your projects, educational or otherwise, to raise awareness? What have been some of the key learnings for you through these training programs?

Esther: Thanks to our historical roots and the organisation of the festival, we can maintain a connection with students and their concerns. We strive to welcome them into our organisation as much as possible through internships and immersive experiences, showing them that there are many possibilities for their career paths and that alternatives to traditional agencies exist. What we take away from the projects we carry out is that it is essential to be on the ground to understand the issues at stake, but also to propose a coherent response that is adapted to the uses and users. Before each intervention, we try to create spaces for listening and understanding with the main stakeholders.

We want to move away from the architect's position as the sole expert on a project and give a voice to the various stakeholders: residents, artisans, local authorities, etc., to help find the best solution—one that will have the least impact on material and immaterial resources. We propose and insist that our projects include a mission dedicated to involving future users of the site, consultation and even workshops to raise awareness of reuse in construction. In our training courses, practical exercises in the field are just as important as theoretical exercises.

Anushka: Bellastock treats sustainability as a cultural and material question as opposed to a technical one. How do you hope to reshape public and professional perceptions of sustainable architecture?

Hugo: In contrast to a techno-solutionist view of sustainability, we propose frugal and low-tech approaches to architecture that place ecological, social and cultural issues on an equal footing. Our approach refocuses attention on care, building renovation, material reuse, but also on the people who construct buildings, the democratic access to construction techniques and the appropriation of uses and places by inhabitants.

We use several means to reshape perceptions: assistance for architects, public decision-makers, companies involved in construction projects, cultural events, workshops, publications and conferences. Our strength lies in having sufficient visibility to be heard by public authorities, but also in our intense fieldwork to help small businesses on the ground. Ultimately, our usefulness lies in making a modest contribution to the infrastructure for a future circular economy, when public policymakers and the construction sector will decide to put in the necessary means for an ecological and social transition.

Anushka: Looking ahead, what are some key visions for Bellastock’s upcoming biennale? What do you hope to do differently compared to the previous editions?

Esther: The festival's transformation into a biennial event coincides with our 20th anniversary. In line with this dynamic and a phase of ongoing reflection with our members, the festival will take place over two consecutive years, in a biennial format that will allow us to better anchor ourselves in the territory. The construction of the ephemeral city will thus become the climax of a series of events and one-off interventions gradually taking place on a site that will leave the Île-de-France region.

We want to better respond to the needs for regional transformation and offer frugal and relevant architectural and urban solutions to the issues faced by local authorities. It is also about generating more interest among students in experiential learning and bringing teaching closer to learning by doing. We will work with Les Grands Ateliers, who will help us develop the pedagogical offering of the event. Finally, we hope that this biennial event will foster connections and exchanges between audiences, breaking down the barriers between architecture, arts and crafts, and the general public to create dialogue on ecological, cultural and social issues that concern us all.