Success in simplicity = Extensive Green Roof
Plant selection: 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 Roofs 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 system profile, extensive Green Roofs add less weight to a structure than deeper system.
In general, the weight of any Green Roof type and 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. As plants don't care about weight of a Green Roof, but plants care about the amount of plastic elements within a Green Roof. Actually the higher the amount of plastic in a Green Roof solution the higher the costs (and waste) and the lesser preferred growing conditions for the plants. This is simple a fact but we also know that these plastics might not last as long as the structure below. Tip: (Plastic-Eating Microbes)
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.
