Green roofs are a relatively new concept in the landscaping domain – they are related to transforming the terraces of buildings in urban regions into mini landscapes that would help add more green cover in the concrete jungle. One of the challenges with this concept is that the older buildings are not designed to support the additional weight that the green roofs would add to the structure. Over the past decade, the concept of green roofs has evolved to a state where today you can build new structures that support full-fledged gardens and alternative create gardens that can be placed on top of existing structures.
The green gardens can be classified into three categories:
Intensive gardens are the original green roof concepts where a proper garden is constructed on the roof top. These gardens have a deep soil cover going as deep as 20 cms or greater. These structures require a specially designed roof that has a solid block of concrete followed by water proofing membrane, root barrier and an effective drainage layer. On top of these layers ample soil and growing medium is poured for the plats to grow. Intensive gardens can have anything from small shrubs to large trees on the roof tops.
Given their features, the intensive gardens are typically expensive to construct and require special structural design that can support the additional weight. It is obvious that intensive gardens are not ideal for existing building that were not designed for the weight on the roof tops, in other words these gardens cannot be retrofitted.
Another aspect about the intensive roof gardens is that they are proper landscapes and hence require a lot of maintenance. The need regular irrigation, weeding and other maintenance works. As a result, these gardens are not only expensive to build but expensive to maintain.
Extensive gardens are really the other alternative to intensive ones that have been scaled down to be retrofitted on older buildings. The depth of the growing medium is 5-20 cms only. These can be added on top of existing buildings or alternately new building can be designed to support such gardens too. Given the shallow depth of the growing medium, the types of plants that can be planted in such gardens are very limited. Typically vegetables and small shrubs that do not do not grow their roots deep into the soil are the only ones that can be used here.
The extensive gardens are ideal for retrofitting on old buildings. They are comparatively economical and hence favoured by many of the already constructed building that cannot risk or afford intensive gardens.
In a start contrast to the intensive gardens, the extensive gardens are ideally suited for buildings that do not want to invest in maintenance. The extensive gardens are designed to be self-sustaining. They just need to be laid of retrofitted with the necessary support system like the draining and irrigation systems. These gardens can survive with nearly 0% maintenance for years.
These are a trade-off between the low maintenance of extensive gardens and the greater plantation variety of intensive ones. These gardens typically have a much deeper growing medium than the extensive gardens – this allows a wider range of plants to be placed in these gardens giving a much better aesthetic appeal. At the same time, these gardens are designed to survive with minimal maintenance like the extensive gardens.