When creating an extensive green roof, vegetation should be chosen taking into account plants’ abilities for handling severe temperature changes, extreme weather conditions, drought and wind. Sedum is a genus belonging to the crassules (Crassulaceae) family with more than 500 species worldwide. These plants typically store water well and tolerate changing conditions. Another feature of Sedums – that makes them suitable for green roofs – is their shallow root system. Compared to other plants they need less nutrients and are easy to keep, drought-tolerant, infectious diseases are unusual to them, and they are neither susceptible to pests.
Covering roofs with vegetation is not a brand new idea. Flat roofs with hanging gardens appeared in ancient times as well. They indeed had traditions dating back hundreds of years, especially in areas with extreme climate conditions due to their temperature leverage effect. To date, traditions for building green roofs are kept in the Nordic countries, Iceland and Greenland. Because of their numerous beneficial features and effects, in several countries – just as in Hungary – more and more modern constructions take over this solution. A green roof neither requires intensive care nor maintenance. It performs a protective function against negative environmental impacts. It retains or decreases drainage flow rate when large quantity of rain falling rapidly, thereby, also reducing loads for ditches. In summer, it has a cooling effect, it also reduces the temperature of the slab and its immediate surroundings. In winter, it has insulating benefits. It provides protection for the roof, thus increasing its lifetime. Green roofs even have sound insulation properties, as well as dust- and pollen-binding nature. When installing a green roof, the primary concern is not the creation of a traditional garden function; rather, the goal is to transform an uninviting and empty surface into a living and breathing green space.