These development techniques aim to maximize breeding, feeding, and nesting conditions for insect and bird communities in open environments.
Recent studies (GROOVES) demonstrate that traditional extensive green roofs, homogeneous in terms of facies (uniform flat roofs) and species (generally Stonecrops or Sedums), ultimately offer limited benefits for biodiversity. This is where 'wild' and 'brown roofs' become particularly relevant.
The 'wild roof' concept involves designing roofs that are primarily functional for target species, providing essential food resources (nectar-rich plants, deadwood, watering holes, seeds, etc.) and shelters (sand for wild pollinator nesting sites, stumps, nesting boxes, etc.).
As for the 'brown roof' concept, it involves creating a diversity of soil types and varying their depths. No plant species are planted or sown. It serves as an observatory for spontaneous ruderal flora (which grows in anthropized environments): seeds are carried by wind (anemochory) or by animals (zoochory). Plants grow naturally and adapt to the created conditions. The varied physiognomy of these associations leads to a greater potential for spontaneous flora diversity, both in terms of specific and genetic diversity.
In summary, the design parameters for this type of biodiversity-enhancing roof include:
At Sinteo, our ecologists are currently working on a project directly implementing these specifications: the Altarea Innolin project in Mérignac, which will soon host Groupama's teams. The Innolin roofs therefore follow the 'wild roof' and 'brown roof' principles, notably with the installation of two rooftop ponds. The advantage of these designs, beyond their significantly richer biodiversity potential compared to traditional green roofs, lies in their self-management: no maintenance is required, nor is irrigation, as these biodiversity spaces closely mimic the functioning of an ecosystem, without human intervention.
However, patience will be required to achieve a fully vegetated space. It is the natural action of birds, wind, and other insects that will enable the development of various vegetation strata over time: root, moss, low herbaceous, high herbaceous, and shrub layers.
It should also be noted that this approach offers a means to recycle part of the materials from an existing site during restructuring: various substrates such as crushed brick, sand, or gravel will integrate perfectly for the creation of the brown roof.
In summary, even if the implementation of these wild and brown roofs may not be the most aesthetically pleasing at the outset, our ecologists favor them over traditional green roofs, which would have a significantly lesser positive impact on local biodiversity at the project's core. Furthermore, a wild and/or brown roof is far more natural and resilient than a human-made green space (due to the absence of plastic modules and other industrialized objects).
Therefore, to meet both client expectations and to move towards site renaturation, our ecologists recommend combining two solutions: implementing lush green roofs to address the aesthetic appeal of a site on visible terraces, and focusing on wild and spontaneous vegetation for less visible roofs. However, as seen in the Innolin project, the architectural and landscape design teams took pleasure in creating a master plan featuring a geometrically twisted wild/brown roof, which also offers an interesting aesthetic! The evolution of these roofs is subject to scientific monitoring, and upcoming drone imagery should allow us to track the environmental changes.
To be continued!