Extensive roof planting
The objective of extensive planting is to have lightweight natural vegetation requiring minimal maintenance. Sedum species are commonly used as stock plants. Supplemented with drought-resistant herbs, sedum/herb plant communities can also be established.(kopie 1)
A standard multi-layer design for extensive plantings has become established, involving separate layers for different functions: supporting vegetation, filtering and drainage. The vegetation supporting layer is a substrate with a mineral composition and only a small proportion of organic matter. The substrate must be capable of storing water and nutrients and of providing plants with sufficient root space
Excess water that cannot be taken up by the plants should be reliably removed. A drainage layer, which may combine the functions of water storage and drainage, is incorporated for this purpose. Between the substrate and the drainage layer is a filter fleece for retaining fine particles from the substrate, thereby ensuring that the drainage system will continue to function in the long term.
(kopie 2)
The weight of the system is essentially determined by the substrate. The weight of the standard mineral substrates is approx. 10 to 13 kg/m² per cm layer thickness in a water-saturated state. For a sedum planting, a substrate depth of at least 6 cm is recommended. When the vegetation and the filter and drainage layers are included, the weight will amount to around 70 to 100 kg/m². Sedum/herb plantings with a minimum of 8 cm of root space weigh upwards of 90 to 130 kg/m².
Using a special lightweight green roof system for roof structures with a lower load-bearing capacity, the total weight can be kept to below 70 kg/m². However, the vegetation will then have only limited root space. Extensive plantings are low-maintenance, but not maintenance-free. Regular weeding and fertilisation of the substrate when necessary are the most important maintenance tasks.
Watering - at least with established extensive roof plantings - is not necessary. Only with new plantings, some emergency watering may become necessary in dry periods. Until the desired vegetation has established itself as a total cover of the entire roof area after one or two seasons, a little more maintenance may be necessary Thereafter, two maintenance visits per year should suffice, ideally one in early spring and one in the autumn.