The various works presented below show multiple types of experiments, going from the conception of technical devices to interviews of experts and theorization of our built projects. We believe these sorts of experiments to be essential for innovative architectural projects.


Land Use Coefficient

A new regulation?

COBlogo Initiated on the occasion of the ‘Reinvent Paris’ consultation (Réinventer Paris), the design of the 183, rue Ordener plot is a manifesto project testing the limits of the proximity between men and nature, in an urban environment. While Paris has got a very rich ecological heritage we tend to observe its uneven geographical repartition. The 18th arrondissement is one the six less vegetated ones, which turn out to be the more densely populated districts of the city. Moreover, this arrondissement contains a great number of small green areas, adding up to only 3% of its whole surface. The district map is thus characterised by a ‘marbling effect’: the scattered vegetation appears to be broken up and compressed by the buildings.

On this narrow plot, the project includes the construction of about twenty housing units and a nursery. A 28-metre high gable wall borders the site. Its ‘non-constructibility’ constitutes a strong design constraint. Nonetheless, this surface turns out to be a real opportunity, implying a reflection on what could become of these forlorn urban places. Here, the wall becomes an ecosystem, accompanying local residents along their way to the heart of the block. Stairs lead to footbridges and green terraces clinging to the gable wall, like ‘greenery shelves’. The garden thus created is a suspended landscape, accessible at various levels above the ground. The gable wall is clad with a structure receiving biodiversity through a series of green terraces and a three-dimensional network multiplying open surfaces for vegetation and wildlife.

COBlogo2 Based on the principle of ecological continuities at a territorial level, the project is envisioned as an experiment which could be declined as a paradigm on many other sites. Just as a fractal, its setting up implies a reflection on various scales: the inhabitant, the block, the city… This competition gave us the opportunity to start our prospective approach by offering the city council a new regulatory tool in order to measure the biodiversity density on the plot. Inspired from the formerly used Land Use Coefficient (Coefficient d’Occupation des Sols), we would establish a ratio between the green surfaces and the whole plot surface, by a simple calculation. The ratio would be equal to 1 for a totally vegetated plot (on the ground surface), and would reduce as the built surface would increase. However, on a densely constructed plot, the ratio could increase, the calculation taking into account all types of green surfaces (walls, roofs, terraces…). This tool would allow to include the forlorn spaces in a global, innovative reflection on the process to a greener city. Combined with the local urban regulations (Plan Local d’Urbanisme), the ratio of biodiversity occupation (Coefficient d’Occupation de la Biodiversité) would adapt according to each district in need of green areas. A natural rebalancing could then develop, modifying the cityscape, as well as the way we look upon this new type of density. ■


A living wall for the school of Sciences and Biodiversity

The design of a concrete-block “living wall” for the school of Sciences and Biodiversity  in Boulogne-Billancourt was the context for a truly experimental work. The wall designed along with Biodiversita, office of applied ecology, already hosts the local fauna and flora.

The Boulogne project’s ‘bark’ formed by the inhabited wall is made out of prefabricated concrete blocks. Piled up in a staggered pattern, they split the wall in thousands of edges, breaches, overhangs, crannies… This lay out multiplies angles and situations, thus easing the colonisation process for the various species expected on the site. The blocks have been given two different textures. The visible side has a smooth, polished aspect and reflects light. The other faces are sandblasted: the concrete’s uneven aggregate appears, thus creating a wall of rough and rugged concretions. The upper and lateral splines multiply the exchange surfaces with the outside environment and channel the water, providing a propitious terrain for vegetal development while avoiding runoffs on the visible side as much as possible.


Interview with Aurélien Huguet, researcher in ecology

We met Aurélien Huguet at the very beginning of the school of Sciences and Biodiversityproject. Biodiversita, the office of applied ecology he founded along with Florent Yvert, had set up a programme of green roof and inhabited wall. We answered to these prescriptions by developing the concrete block wall and its very singular geometry. Through numerous exchanges, we defined together the reception capabilities of the green wall and roof, regarding the fauna and flora.

Chartier Dalix: Throughout the reflections we develop about the buildings’ envelopes and the way they operate, we like to use the term ‘exchange surface’. The wall in Boulogne was designed as an exchange surface, between up and down, in its depth, and in its participation to the creation of a milieu.
Aurélien Huguet: Yes, we could compare this to the bowel’s microvilli: we increase significantly the possible exchange surfaces… and speaking of environment, the effectiveness of your wall lays in its ability to:
- multiply the geometrical conditions (chaos, ledges, accidents),
- multiply the potential for colonisation (thanks to the blocks developing on the whole façade, which increase the range of usable habitat)
- vary the angles of the blocks, and therefore of the nest boxes, on a single façade
- provide rough surfaces to gather fallen material from the roof
- settle a water network through these surfaces (grooving and flutes)
- provide a depth gradient and buffer zones (thanks to the overlapping blocks and embedded zones) in order to widen the scope of possibilities.
We create the necessary conditions for a typical old-wall vegetal colonisation. To achieve this result, we will have to wait for ‘micro-grounds’ to form (this might take 5, 10, 20 years). The formation of these ‘micro-grounds’, necessary to old-wall vegetation, takes place over time. It is a matter of earth, dust, and micro particles accumulation, spread via birds or wind. This basic ‘matrix’ enables the colonisation. Eventually, a living environment specifically adapted to these extreme conditions shall set up.

CD: When working together, we dealt with the questions of depth and overlay of elements to favour a cryptic biodiversity.
AH: Cryptic means invisible, hidden. It is all that one cannot see with the naked eye, but which will make everything possible. Having designed the thickness of the blocks and not only their outside surface will enable the development of micro-environments much different from those on the exterior of the wall: first because of the thickness of these ‘micro-grounds’ building up with time (there are much more types of possible grounds in-between the blocks than in the outside crannies, and therefore, different potential species may be found), and second, because it creates buffer zones less exposed to stress and atmospheric conditions. Being deeper, these provide much more stable conditions than the surface of the blocks, a difference akin to that between topsoil and deep soil –but at a much finer scale, that of the ‘micro-ground’ and ‘micro-environment’. The first major spontaneous colonisations will certainly take place in these areas.

CD: Today we realize that the ‘inhabited wall’ is beginning to really operate as such, in terms of hosting the fauna: just the other day, we watched together a titmouse flying out of a block on the south façade, above the gymnasium’s entrance…
AH: This is a good sign! It will lead the way to others! We worked block by block on the nest boxes’ implantation, so as to consider every possible situation. We multiplied the orientations and angles, diversified the altimetry, but also defined the boxes’ positions and volumes as well as the different sizes and the exits’ lay out, according to each targeted species. This titmouse settled in a nest box intended for it. This system also provides overhangs and ledges, which are perfect for swallows. Maybe we will be able to observe common pipistrelles or plecotus hunting in the Trapèze Park or along the Seine and flying around here. I initially asked for cracks and fissures in the materials of the building’s façade, but you offered a system introducing the notion of ‘interstice’ in its very composition and construction: the blocks’ assembly allowed to expand the fissure principle, and above all, to make them more numerous and diversified.

CD: You refer to the individual design of each block, but we ultimately got to work with prefabricated elements, integrated to an industrial manufacturing scheme and rhythm.
AH: The nest boxes lay out was designed ‘by hand’, but you managed to make it possible in terms of cost and construction. It is all the more interesting because the whole approach then becomes feasible: we will see the evolution over time, but if it works, this will become an exportable solution.

CD: Do you believe that regarding this type of experiment on ‘colonisable’ walls, the use of concrete is relevant?
AH: I think it is, as it enables to create interstices, to receive the flora, and to ultimately acquire the ‘old-wall characteristics’. Concrete has got the ability to keep stable properties over time. Its surface erodes like stone, which allows to receive vegetation after a long maturation… We targeted animal and vegetal species which will settle in the crannies, and which are therefore adapted to this material.

CD: The colonisation process begins with the apparition of algae, moss and green stains. The concrete blocks are currently turning green and getting dirty, especially on the northern and western façades. It turns out to be hard for the public to accept the fact that the building ages, ‘micro-deteriorates’, appears dirty, unmaintained…
AH: This is fine, this is the first stage… It is necessary to inform the public by explaining that this is no degradation, but a maturation. The building’s skin is maturing, and will reach maturity through this transformation and colonisation by living organisms.

CD: The wall needs time, whereas the roof very quickly became the wooded massif we hoped for. With more than 1m of topsoil, this already is an actual high forest. The smaller topsoil thickness below the forest edge (the ‘hem’) and below the meadow (50cm) allows to keep the desired balance, the stratification. It appears that such an off-ground composition does not have any equivalent so far, in the existing constructions.
AH: We have only tested this composition in open ground yet. This is one of our typical regional compositions: the forest edge. This passage between forest and meadow is frequently composed of recolonising shrubland. One of the issues was to create edges: the ecotones. In other words, transition areas between different environments, where most of the exchanges take place. These are usually the most valuable areas. This is what we reproduced on the roof: a hem between a meadow area and a forest. The forest edge is created by the association of these three layers and by this gradient upward movement from low vegetation to wooded area.

CD: When the building was delivered we were all rather surprised by the surrounding density. May this be a problem, regarding colonisation? Is a ‘wild’ environment compatible with all these buildings, only six metres away from the school?
AH: It is possible for an environment to develop into this density… To make things easier, we must link as many habitats as possible. When it comes to ecological continuity, we are dealing with two different types. The physical continuity is almost impossible to maintain in a dense city. We try to preserve it in ‘peri-urban’ zones through the protection of key areas, blue-green infrastructures, buffer strips and wildlife corridors… But in our situation, we are dealing with ‘stepping stones’ between separate environments including the Seine, the Trapèze Park, and a bit further, Clamart, Meudon, Viroflay… The idea is to create a possible stop. An oasis in the desert. In an almost sterile urban context, we create a place which turns out to be welcoming. This site is hard to colonise, of course, but once the process has started it becomes all the more precious.

CD: So you do not consider the urban density as an obstacle to the presence of biodiversity?
AH: Let us be clear: it depends on the species. It is an obstacle for terrestrial species. But concerning flying species, the urban density will not preclude colonisation. The real issue is the accessible height. We know that all ground-level species are able to colonise more or less directly up to the fourth floor (butterflies, beetles…). It gets more complicated above this level. A bumblebee cannot forage on the rooftop of a high-rise… The Boulogne school being shaped as a hill, it offers possible communications between the different levels, thanks to the wall and ramps you designed. If we can enable a green path, a continuity between the lower and upper levels, many things may be possible. When aiming to create a colonisable environment, the density isn’t really the issue, but rather the altimetry and the continuity solutions.

CD: The extinction of numerous species since 30 or 40 years is linked to a hostile construction mode towards the implantation of biodiversity. According to you, which would be the requirements to restore favourable conditions?
AH: Knowing that each project requires a specific reflection towards its context, morphology and programme, these are the few points we could list:
- take the height into account
- select native species (in order to favour the survival of ordinary nature against exotic species)
- work on a precise ground composition (avoid bulk topsoil)
- define a management method and work along with the managers from the beginning of the conception phase
- work on the building’s envelope in order to create thicknesses and crannies, preferring ‘welcoming’ materials: wood makes it easy to design nest boxes, concrete enables to include vegetation… In contrast, metal and glass offer far fewer colonisation opportunities.
In any case, dealing with biodiversity, the users’ tolerance is a crucial topic: how far can we tolerate this closeness to nature? This is a cultural and educational issue.

CD: Today’s trend is towards architectural and urban revegetation. Nature colonises roofs, façades… every call for projects implies the implantation of biodiversity. How can we explain all these convergences of interests regarding urban biodiversity?
AH: In fact, the interest of urban biodiversity is twofold: on the one hand, it concerns biodiversity itself, and on the other, the city-dwellers.
Ordinary nature is disappearing from today’s city when it was still present yesterday. A few decades back, Paris used to be surrounded by fallow lands and small agricultural plots. Nowadays, we are separated from the first ‘little natural spots’ by industrial areas, motorway junctions, sterile agricultural plains… Yet, we all wish to be able to gaze at birds, to show them to our children otherwise than on a T.V screen, and to appropriate them: ‘this is my butterfly’, ‘here’s my robin’ (the one I see every day)… Being able to watch nature from home and in familiar places ends up generating vocations: we love and protect what we know. To a city-dweller, this represents the opportunity to witness life’s evolution, to watch seasons unfold…

CD: This is regarding the city-dweller, but what about biodiversity?
AH: Working in the city brings not to consider the urban environment as sterile, by setting up links, environmental continuities. There are generally more native species in an urban environment than, for example, in a fenceless great intensive-agriculture plain, which creates biological and vegetal deserts. Conversely, there are more than a hundred different bird species within Paris thanks to the old parks: le Père-Lachaise, les Buttes-Chaumont… a full range of urban biodiversity, also to be found in/on the buildings. Swiss studies made it possible to inventory up to 300 beetle species on the buildings’ green roofs. We build here and we live here. The projects are made here: let’s take the means where they are, and let’s take part in ordinary nature’s conservation before it disappears.
For about forty years I have witnessed a degradation, a depletion, a normalisation of common diversity: this is equally due to the public development policies as to the individual behaviours, by lack of culture and interest… But today, the global perception has changed. We have gone from protecting ourselves from nature, to protecting nature from ourselves. And there is plenty to do. The time and resilience scales we are dealing with are not those of overall problems such as the global warming: each small action can lead very quickly to concrete results. As soon as next spring, the children in Boulogne will see titmice nest into the walls of their school. ■


Willing to imagine the city as a vast living environment, we want to create harmony between our projects and their contexts inside the cityscape.

Arcueil BD

Seeing an architecture project as part of a landscape implies to consider the site with a much broader perception, quite the reverse of a building designed as a solitary object. In this regard, and especially at a certain scale, a building can be thought of as a physical geography: it becomes an inhabited landscape.

With such a vision of architecture, the building takes its place in the city as part of a whole. The residents’ perspectives are seen as the starting point. This provides an approach which is at the same time a local and an overall one. It is part of a complex whole including a series of territorial elements: its scale, its formation, its history. It is an integral part of the ongoing urban sedimentation process.


The office building project in the Batignolles district, Paris 17th arrondissement, originates from a topographical study of the cityscape. As it is positioned directly above the void created by the Gare Saint-Lazare railways entering the city, the building contributes to the geological section effect in this part of the city. In this area, Paris displays a rugged terrain, heights and depressions, and vast empty spaces. This urban geography, as some sort of anthropocene morphological accident, inspires the geometric variations of the building. Constituted in a ‘ribbon’ plan, it shows an open façade to the railways, the street and the park, as an answer to this great landscape context. Hence, in the manner of the Möbius strip, the interior and exterior spaces become entangled on all sides of the building, offering at the same time free flow and an outside visual continuity from the ground floor to the roof.


Tafanel BD Located in front of the Centquatre cultural facility and wedged between the Éole garden and the Gare de l’Est railways, the logistics centre of the Tafanel company is designed as an artificial landscape, consisting of a large pleated cloth forming a succession of multi-directional sheds. On the street side, a 450 metre-linear façade faces frontally the preexisting buildings. It is composed of wired glass overlapped by a layer of anodized aluminium. The glass was superimposed to an old blind wall. This former street art support thus represents the first layer of a stratification turning into a changing mirror, reflecting the city and the evolutions of the daylight. On the railways side, the roof displays a regular pattern produced by the folds descending onto the façade, multiplying the acceleration/deceleration effect and offering a kinetic vision to the passengers of the trains.

Due to its geographical presence, the landscape-building’s relation to its environment can be seen as a sort of radiance: it is generated by the context and affects it in return, in a motion of interaction. The landscape-building bears its immediate environment and transforms it.

Collège Moulins

The Moulins secondary school in Lille is located on a corner plot at a crossroads between the Boulevard d’Alsace and the rue d’Arras, facing the aerial metro. This situation calls for a reflection about the perception of urban facilities at different scales.

Collège Moulins BD

The first approach is that of the building as seen from afar -its masses, its roofs- in a rather stealthy vision. Seen from the aerial metro, or from the nearby buildings, the upper part is treated as a continuum, playing with the volumetric topography of its masses. The various programmatic elements are clearly identifiable: the secondary school, the sports hall, the boarding school, the rehearsal room. This geography is unified by a supple pre-weathered zinc envelope following the volume’s shape, and creating an emblematic urban signal for the facility itself as well as for the neighbourhood.

The second approach, which is more local, is that of the relation between the neighbourhood and the facility. It refers to the pedestrian’s point of view, whose gaze is at the ground floor and access level. This first level was made as porous and transparent as possible, in order to offer a depth of field allowing to grasp the whole plot straight from the street.

Collège de la Paix

This secondary school near Paris, in Issy-les-Moulineaux, was designed with the aim to assign a function to its own geography. The playground follows a programmatic backbone connecting the common spaces (restoration, courtyard, hall). This diagonal axis cuts through the ring-shaped plan, creating a series of additional outdoor spaces offered to the pupils. The path thus acquires great fluidity, allowing to walk freely from the playground up to the library, the theatre, the arts room, and so on, up to the rooftop. The facility turns into a spatial experiment within an alternatively vegetal and mineral topography. ■