Success in simplicity
An extensive Green Roof is home for plants with special adaption to extreme site conditions and high regeneration capacity. Additionally, it is characterized by moos, succulent (Sedum), and small herbaceous plants including drought tolerant grasses. Thus extensive Green Roof require low maintenance and have no permanent installed irrigation system, because it would defeat the purpose.
Typically, the system depth for an extensive Green Roofs rages from 4 to 6 inches (10 cm to 15 cm). Although there are shallower extensive Green Roof systems on the market, they are only resilient in specific climate zones. E.g. temperate climate zones with Gulf Stream influence, like northern Europe. Because of the shallow profile, extensive Green Roofs also add less weight to a structure than deeper system.
In general, the weight of any Green Roof system is not a quality criteria. In fact, plants do not care about the weight. After all, plants care about the porosity of materials, Air-to-Water Ratio, and nutrient exchange capacity to name a few. Since all Green Roofs are supposed to retain water (for the plants), the weight of a system mainly depends and varies on the amount of water within the system. The specific weight of water is the same around worldwide.
Vegetation
The vegetation on extensive green roofs is subject to natural reshuffling. Plant species migrate or new plants species settle. If there is the desire to retain or keep a certain vegetation palette, a specific vegetation pattern or a regular full-scale flowering of its vegetation, additional maintenance efforts are necessary with an appropriate supply of nutrients. Sedum-only extensive green roofs require 50-80% more maintenance than a divers extensive greening with natural vegetation dynamic.
Over all, the natural vegetation dynamic creates biodiversity and makes extensive Green Roofs more resilient to Climate Change.
