Green roofs naturally absorb storm water, reduce the amount of dust and withstand high temperatures. It doubles or triples lifespan of roof by protecting the surface from harmful UV rays and acid rain degradation. Reducing of the storm water quantity may contribute in significant cost savings in cities where fee for drain water is applicable. There is increasing support from municipalities for building of green roofs. They provide habitat for wildlife (birds and insects). Each green roof transforms dead space into garden space, returning to the nature what was taken of by building development. There are two major types of green roof: Intensive systems allow to design a park-like setting with paths and resting areas. In contrast, the Extensive system consists of low-growing plants (Sedum….) and requires low maintenance only.
- According to vegetation types: extensive
Extensive Green Roofs
The main objective for extensive green roof is to establish green vegetation with minimal weight and care requirements. Widely used plants are different types of Sedum. During one or two years the plants will cover the whole roof space. The required care is minimal, only from time to time pull weeds and fertilize the soil.
Intensive green roofs
Intensive green roof offers wider choice of design and structure. Intensive systems allow the designer to create park-like setting, they accommodate all types of plants including large shrubs and trees. With correct dimensioning of the vegetation carrier layer, sufficient irrigation and nutrient supply, the conditions for the growth of plants on the roof are almost as good as in the soil. Consideration should be given eg. The stability of species and the possible negative effects of the building, such as blazing facade. Designing intensive gardening and especially the choice of plants according to the object requires relevant expertise. Minimum soil depth for grass, flowering plants and herbs is 20 cm. For larger plants (shrubs, trees) use a simple formula: plant height/10=soil depth. Regular maintaining can be quite involved, irrigation system is highly recommended. Larger plants will also require regular pruning and have to be monitored for health.
- According to the load: light, moderate, heavy
Statics – roof load
Maximum roof load is one of the main objectives when planning the green roof. Intensive green roof weight from 300 kg/m2. Extensive green roof weight is approx. 150 kg/m2 when fully saturated with water, in case of use of soil. Modern methods offer lower weight – approx. 50 kg/m2 when MINERAL UNDERLAY is used. Possible snow cover weight must be added to these VALUES.
- According to roof slope: slight slope, sloping roofs, steep roofs
Modern methods can resolve almost any roof slope. However the steeper roof, the more complicated and more expensive solution exists. Ideal roof slope is up to 15’, in other cases the soil must be protected from landslide. The steeper roof, the more protection must be used, subject to individual consultancy.
- According to cost: economical, other
Each green roof project is individual and unique. The most common example for basic extensive roof with roof slope under 15’ is approximately:
- Complete soil cover, without hydro-isolation: 850 Kč/m2
- Hydro-isolation foil incl. metal flashings: 400 Kč/m2
- Drainage and water storage layer installation:: 150 Kč/m2
- Filtration and protection layer installation:: 100 Kč/m2
- Soil installation: 250 Kč/m2
- Planting: 350 Kč/m2
VAT and delivery cost not included. Planting includes Sedum plants (25pcs/m2). When using plant seeds, the cost can be less. Conversely, significantly more expensive option is the Sedum Carpet. There is a simpler single-layer composition omitting the drainage layer. If it is already on the roof waterproofing, but not resistant to the root penetration, it is possible to lay a special thin root membrane. As a waterproofing membrane we use as standard PVC foil welded, occasionally bonded EPDM membrane and asphalt foils.
- According to the complexity of maintenance
Green roof maintenance
The biggest benefit of extensive green roofs is that they require very little maintenance. To keep the plants in a good shape we recommend inspection at least once a year. Some weeding and soil fertilizing is welcome. Maintaining an intensive roof is the same as maintaining a garden or park. The more we care, the more attractive is the garden appearance.
Green Roof layers