Sought in recent years to produce solar energy, green roofs are now being used to host biodiversity and produce wealth. The nature is back in the city bringing along the vegetal life and its fauna.
While solar power has been monopolizing roofs turning them into financial investments, a parallel movement has emerged aiming at protecting biodiversity and health.
They are ecologists, architects, gardeners, urban farmers or scientists, what brings them together? They are all passionate about plants. Their strength: being logic. Our cities no longer breathe, city dwellers need oxygen and nature functions must be restored before our cities become unfit for life.
Thanks to these innovative individuals, our roofs are now considered an asset for the preservation of biodiversity. They have become lively places where one's can grow, rests, play, harvest...
This trend has emerged to the point that large cities such as Paris*, London, Zurich (to name a few) include or promote green roofs in their urbanism plans and architectural projects. The idea is to make usage of unused surfaces to restore ecological functions affected by urbanization. The role of green roofs is to help refreshing the air in summer but also to trap fine particles and collect the water flow during heavy rains.
For these cities green roofs are a reality now well established in urbanism projects.
Green roofs are now at the beginning of a new era
Till now, green roofs have been limited to the type known as "extensive" due to insurance issues which divided professionals. This consists of roofs with only one type of plant: the sedum. In fact this has caused roofs to be uniform, often reddish and this has eventually discouraged many of those who sought the aesthetic value of the roofs. Extensive type plants roofs have the advantage of being resistant to drought, of having a good coverage and of fixing the substrate. This is what made them successful. But this type of vegetation has a limited contribution to the development of biodiversity and its benefits: the sedum mats are generally not diversified enough and the substrate is too thin to develop biodiversity.
Even though motivated by good intentions, this model will soon come to an end. It will be overtaken by a new design that better supports natural balance and the return of an ecosystem.
* The BioSolaire roof was primarily designed to develop biodiversity and host wildlife. It completely breaks with the former extensive green roofs model.
It is often said that nature does not like the clean-in-order as a consequence basic rules must be followed to create favorable areas for biodiversity. A thicker substrate is needed, plant species must be various and diversified reliefs must be created and small shelters built to accommodate small species of wild fauna.
This design also has the advantage of improving the thermal and water inertia of the roof.
To initiate such a project, it is crucial to know the techniques used by experienced professionals. Init Environment convenes an expert from Switzerland (a country where green roofs are encouraged by state subventions) to share her knowledge about green roof design and implementation *.
Diversity of plant species and species of local origin is emphasized (wild flowers, honey seeds), better adapted to the regional climate. The more species are used the more chances of surviving the extreme conditions that do not support a monoculture the roof has.
We will design and treatment implementation in order to encourage the greatest possible return from using local species
(invertebrates, bees, butterflies and other pollinators).
Technically this type of roofing course requires an interview, which mut quickly pleasure, where the use of dangerous and of course avoided pesticides.
The BioSolar Roofs play the synergy between biodiversity and energy production:
The installation of panels creates shady areas and different moisture level which favor plant diversity and habitats. They
thus provide better living conditions for plants and excellent refuge areas for wildlife.
There is evidence that the vegetation has a positive effect on the production of solar energy. Evapotranspiration of plants help to better cool the photovoltaic panels. This cooling is important because it increases the efficiency of the panels during the warm season in spring and summer.
Another advantage of this combination solar / vegetation on the roof, lies in the weighting function provided by the substrate on the panels.
A future for onlookers
Paris now cultivates its roofs and urban agriculture is getting popular and is expending worldwide. Fashion or pleasure, used to escape routine by some or to return to the simple life by others, it may simply be the ecological transition.
* For more information:
May 4 (Law et Cher) open days to plant professionals, specifiers building, landscape, communities: exchange of experience between Switzerland and the Loir et Cher on the introduction of biodiversity on territory. Presentation of new green roofs and BiosolarRoofs by Nathalie Baumann (ecologist, responsible for the organization and execution of green roofs and BiosolarRoofs for the cities of Zurich, Lausanne and Basel).
5, 6 and 7 May (Law et Cher): training in the design of BiosolarRoofs (design, plant selection and substrates, implementation techniques, maintenance).
Init Environment (Partner BioSolarRoof project):
The Departmental Observatory of Urban Biodiversity of the Seine-Saint-Denis (ODBU)