There are two main utilization options for Green Roofs: one, as a wonderful roof garden with a pleasant view for the owner; the other, an undisturbed habitat for flora and fauna within grey city centres. Both variations provide a broad range of private and public benefits. Deciding on which utilization to focus is crucial and has to be considered as early as the planning stage. In addition, the maximum load bearing capacity, maintenance, plant selection, substrates and the expense budgeting must correspond with the desired Green Roof type.
The following criteria can be used to characterize three different forms of Green Roofs:
|Extensive Green Roof||Semi-Intensive Green Roof||Intensive Green Roof|
|Plant communities||Moss-Sedum-Herbs and Grasses||Grass-Herbs and Shrubs||Lawn or Perennials, Shrubs and Trees|
|System build-up height||60 - 200 mm||120 - 250 mm||150 - 400 mm on underground garages > 1000 mm|
|Weight|| 60 - 150 kg/m2
13 -30 lb/sqft
| 120 - 200 kg/m2
25 - 40 lb/sqft
| 180 - 500 kg/m2
35 - 100 lb/sqft
|Use||Ecological protection layer||Designed Green Roof||Park like garden|
Extensive Green Roofs are well suited to roofs with little load bearing capacity and sites which are not meant to be used as roof gardens. The costs are lower than Simple Intensive or Intensive Green Roofs. The mineral substrate layer, containing little nutrients, is not very deep but suitable for less demanding and low growing plant communities.
Sun, wind and drought are additional stress factors for plants on buildings. Drought-tolerant plant communities, such as, those found in dry mountain environments, coasts, semi-deserts or dry meadows, are visibly adapted to the natural extremes of the local conditions and are preferred species. Mixtures of mosses, succulents, herbs and grasses create pleasant plant communities.
Semi-Intensive Green Roofs in terms of requirements fall in between Extensive and Intensive Green Roof systems. More maintenance, higher costs and more weight are the characteristics for the intermediate Green Roof type compared to that of the Extensive Green Roof.
A deeper substrate level allows more possibilities for the design; various grasses, herbaceous perennials and shrubs such as lavender can be planted while tall growing bushes and trees are still missing.
Lawn, perennials, bushes and trees are possible on Intensive Green Roofs. Walkways, benches, playgrounds or even ponds can be established as additional features on the roof. There are no limitations in design and individuality, but a few things have to be considered.
The Intensive Green Roof system build-up and the selected plant communities have to be harmonious with one another. In addition, the amount of maintenance of Intensive Green Roofs is higher than on Extensive Green Roofs and permanent irrigation and fertilization have to be ensured.