"What are Wild Roof and Brown Roof?

These landscaping techniques are designed to maximize breeding, feeding and nesting conditions for the insect and bird communities of open environments.

Recent studies (GROOVES) have shown that traditional extensive green roofs, homogeneous in terms of facies (uniform flat roofs) and species (generally Orpins or Sedums), are ultimately of little interest to biodiversity. And that's where wild and brown roofs come into their own.

The idea behind the "wild roof" concept is to design roofs that are first and foremost functional for the target species, with food resources (melliferous plants, dead wood, drinking troughs, seeds, etc.) and refuges (sand for wild pollinator villages, stumps, nesting boxes, etc.).

As for the "brown roof" concept, the aim is to achieve a diversity of soil types and thicknesses. No plant species are planted or seeded. This is an observatory of spontaneous ruderal flora (that grows in an anthropized environment): seeds carried by the wind (anemochory) or by animals (zoochory). Plants grow on their own and adapt naturally to the conditions created. The variety of the physiognomy of these associations leads to a greater potential diversity of spontaneous flora, in terms of both specific and genetic diversity.

In summary, the design parameters for this type of roof to promote biodiversity include:

• A variety of roof heights and pitches
• Setting up differentiated zones, particularly with regard to humidity and wind conditions
• The introduction of light and shadow zones
• The creation of mounds and micro-reliefs creating a variety of depths
• The use of substrates with different grain sizes and weights to provide different refuges for different species.
• Adding dead wood, rocks and other natural materials

Direct application

At Sinteo, our ecologists are currently working on a project that directly applies these prescriptions: the Altarea Innolin project in Mérignac, which will soon be home to Groupama's teams. Innolin's roofs follow the "wild roof" and "brown roof" principles, with two rooftop ponds in particular. The advantage of these arrangements, in addition to the much greater potential for hosting biodiversity than a traditional green roof, lies in their self-management: no maintenance is required, nor is watering necessary, as these biodiversity spaces are as close as possible to the functioning of an ecosystem, without human intervention.

On the other hand, you'll need to be patient if you want to create a vegetated area. It's the natural work of birds, wind and other insects that will enable the development of different plant strata over time: root, muscular, low herbaceous, high herbaceous and shrubby.

It's also a way of recycling some of the materials on an existing site as part of a restructuring project: different substrates such as crushed brick, sand or gravel can be perfectly integrated to create the brown roof.

In short, even if wild and brown roofs are not the most aesthetically pleasing at the start of operation, our ecologists prefer them to traditional green roofs, which will have far less positive impact on the local biodiversity at the heart of the project. What's more, a wild and/or brown roof is much more natural and resilient than a man-made green space (absence of plastic modules and other industrialized objects).

So, in order to meet both the expectations of the project owners and to move towards renaturation of the site, our ecologists recommend combining the 2 solutions of installing a green vegetated roof to meet the aesthetic interest of a site on terraces exposed to views, and working on wild and spontaneous vegetation on less visible roofs. However, as with the Innolin project, the teams of architects and landscape architects will have taken great pleasure in creating a mass plan with a wild/brown roof with a geometric and twisted layout, the aesthetics of which are also interesting! The evolution of these roofs is the subject of scientific monitoring, and future drone images should enable us to follow the evolution of the environment.

To be continued!