1. History and challenges

Rooftop vegetation is not a recent invention, having already existed in the 7th century B.C., as witnessed by the famous Hanging Gardens of Babylon (or Gardens of Semiramis), one of the Seven Wonders of the World.

Green roofs have been used for centuries in Scandinavian countries to protect dwellings from the cold and heat, protect roof waterproofing and create a certain osmosis between landscape and architecture. Some traditional houses, known as "Norwegian chalets", even have double-sloped roofs supporting a thick layer of vegetation.

In other traditional societies, whether in Turkey, Mongolia or among certain Amerindian peoples, the desired or accepted presence of plants on roofs is normal, as they help to cool interior spaces in summer.

In twentieth-century architecture, the garden terrace has gradually become...