France is one of the green roof leaders in Europe, but still far from the number-one country – Germany – which creates 10 million m² of revegetation per year.
Historically, green roofing has been funded by public bodies or entities – for use on hospitals, schools and other public buildings – but private promoters and property companies are currently expressing much more interest in green roofs. In addition, French regulations are accelerating the adoption of green roofs: it is now mandatory to revegetate commercial structures of more than 1 000 m² surface. While there are voices who denounce the financial constraints of such regulations, roof revegetation also brings new opportunities to commercial buildings, especially shopping centers. Green roofs can also be a way to improve the customer experience – and ultimately revenue – like for Galeries Lafayette and Le Printemps in Paris.
Green roofing technologies are strongly connected to sealing and waterproofing technologies, which is why many manufacturers are primarily insulation experts, like Soprema (and its Sopranature solution), as well as Sika. Apart from waterproofing, the other key ingredient for sustainable roofs is root-penetration resistance. Inverted roofing is the typical construction method for green roofs, which means that the isolation materials, like XPS (extruded polystyrene) or PIR (polyisocyanurate) – as opposed to rockwool – is placed above the waterproofing membrane, which can be bituminous, PVC, EPDM or TPO.
Major advantages of green roofs are their durability, reinforced insulation, air-quality improvement, noise reduction and aesthetics. On the other end, some technical challenges remain: the revegetation of ancient buildings is complex due to often-inadequate structural elements; people-accessibility proves complicated, as roofing systems must bear people’s weight; and systems’ manufacturers are developing easy-to-install solutions to allow higher installation rate. Another challenge is cost: the current price range is quite broad, as basic green-roof systems start at 30-35€/m², but can rise to 300€/m2.