It is undoubtedly well known that the irrational development of the built environment, the illegal construction and the limitation of the available public city spaces and green spaces, have caused intolerable environmental conditions and aesthetic downgrading of the image of cities.
On the contrary, the meaning and the role of green spaces have been recognized and have become a research subject for many scientists who are engaged with the planning elements of a city. One of the scarce ways of intervention in order to restore the natural elements in cities today, is the creation of planted roofs.
It is well noted that installing a planted roof can offer beneficial environmental, energy, aesthetical, constructional and social effects, such as dust absorption, noise reduction, improvement of roof insulation value, improvement of the microclimate conditions, aesthetic improvement of space, reduction of energy costs for heating and cooling, as well as reduction of the urban heat island effect, provision of amenity space for users, management of storm water, increase of roof life span and provision of habitat for insects, animals and plants. On the other hand, some disadvantages in the use of planted roofs include the extra cost, the static burden of the structure, moisture, the difficulty in repairing any damages of the different layers of the construction and the need of continuous care of the roof garden.
Nowadays, there are three different categories of green roofs which are divided according to the depth of planting medium and the amount of maintenance that they need. The first one is the extensive type which is frequently being used on building roofs. It can be installed in various terraces and it can be designed to be self sustaining by using plants which are typically low growing ground cover and are sun and drought tolerant. The second one is the semi-intensive, which requires a reasonable depth of soil so that small plants can grow and the third one is the intensive type, which is characterized by the thick depth of soil and the heavy weights added to the structure. All kinds of plants, from small rockery type plants to shrubs and even trees, can thrive on these constructions.
The design factors that one must take into account before starting the construction of a green roof are the strength of the supporting structure, the climatic conditions, the location of the proposed garden (height, size, slope and orientation), the use and the aesthetic preferences.
In foreign countries many communal authorities offer motives in order to adopt the measure of developing the idea of the green roofs, not only for the aesthetic improvement of cities, but also for the confronting of different kinds of problems, such as floods and the pollution of the atmosphere. On the other hand, these constructions are not yet well known in Greece and the result is that there are thousands of square meters of roofs unexploited, abandoned and without any specific use. These roofs could, after a proper study, be converted to islets of green spaces and play a significant part in the improvement of the environment and the quality of life.
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