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15 June 2017
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21 May 2019

The Artillerie site: “a true lesson in sustainability”

Franck Boutté, directeur de l'agence Franck Boutté Consultants

Crédits photo : Jean-Marie Heidinger

Part of the consortium selected for the redevelopment of the Artillerie campus, the Franck Boutté agency advises Sciences Po on sustainable development issues. An interview with its founder, for whom the key challenge of such a project is not so much the quest for environmental certifications as the delicate consideration of the existing buildings.

Your agency extols its multidisciplinary outlook and the importance of combining different approaches. What does this consist of?

My outlook is above all the result of personal experience, in contrast to the rigidities of some higher education institutions. As a student at the École des Ponts ParisTech, I was told that if I went on to study architecture, this would devalue my engineering degree. I enrolled at the National School of Architecture, Paris-Belleville, but the teachers there were no better when they learned about my background in engineering. People weren’t open to multidisciplinary approaches at the time.

I was eventually able to transform this hybrid positioning into a real approach at the agency that I founded in 2004. We work on projects by developing matrix approaches, using tools that allow us to draw upon multiple perspectives. One such example would be inviting an energy engineer and an urban planner to discuss the design of an energy supply model for a district. One will think about sunlight factors, wind exposure, the properties of the existing habitat and regulatory constraints. The other will be sensitive to the development of public spaces or the mobility possibilities for the users of the space. Their questioning is based on technical analyses carried out using software. By overlapping these various interpretation methods and converging them on specific points, we create the framework for a spatial approach. It’s never a question of imposing an over-optimised model, but rather of providing an answer linked to a particular context, a population, a story.

How do you deal with the constraints of environmental certification?

I try to ensure that the certification is not a straitjacket or a hindrance but instead stimulates inventiveness. Environmental engineering is a ‘geometrically variable’ occupation. About ten years ago, sustainable development was an emerging issue in the project management sector: only a few players really mastered an understanding of it. Today, everyone seems to think they know about sustainable development. But when gaining certification becomes the primary objective, it’s the degree zero of environmental issues…

On the Artillerie project, all the members of the consortium carry out their work according to the same guiding principle: the reinterpretation of a unique historical heritage. For us, it’s a question of understanding the intrinsic ecology of each building, putting together an intervention that respects both the strengths and weaknesses of the existing structure.

At times this has led us to rally against our own profession. All of the environmental frames of reference are established in accordance with the standards for new construction: they aren’t designed for work on existing material. If we want old buildings to meet the requirements of today’s energy efficient labels, we have to carry out additional works. Insulate from the inside, for example. But if we did this, the building would no longer have the capacity to exchange air with the outside and a dual-flow mechanical ventilation system would need to be installed. And then to avoid overheating, air conditioning would have to be added.

So how do you adapt to all these constraints? Can you give an example?

Let’s take the example of the cloister in the Sébastopol courtyard  where we’ve had to review the energy strategies implemented in the past. What are its assets? A substantial thermal inertia capacity; a high ceiling that ensures summer comfort with warm air accumulating without disturbing the occupants; high windows too, which generate thermal self-regulation and good air circulation.

Its disadvantages are typical of this type of building: a cold wall effect, a lack of airtightness, and thermal weakness of the building envelope that makes energy consumption high in winter.

The solution we found was to apply a lime and hemp plaster to the walls:  the cold wall effect is removed while insulation is improved and thermal inertia is maintained. The limited air permeability is transformed into an asset. The building envelope is used in the air renewal strategy: the fresh air blown into the premises is evacuated naturally by the building envelope.

I suppose that from one building to another, the solutions you provide are tailor-made.

Indeed. For the Pavilion overlooking the Gribeauval courtyard, a new building that we wanted to be a glazed construction, the problems are very different.  

But it is part of an architectural whole. The redevelopment of the Artillerie site invites us to situate ourselves within a much bigger picture. Over the centuries, the structural generosity of the buildings has enabled them to be adapted to a diverse range of uses and users without changing the identity of the buildings. It’s a form of resilience that must not be altered, and it’s a veritable lesson in sustainability. It’s also an invitation to think reversibly: the solutions that we provide must be able to evolve. During the design phase, we focus on testing the robustness of the solutions proposed for the diversity of uses: how does a building react if its users don’t use it in the way that was anticipated in the modelling? But of course we can only put forward hypotheses. This is the frustration inherent in construction project management: we deliver buildings without knowing how they will really be occupied, how they will be used in reality. It’s also the beginning an exciting story: only the actual use of a building can determine its true environmental impact.