Maintenance
Classification green roofs
Green roofs can be classified in different ways. The German Forschungsgesellschaft Landschaftentwicklung Landschaftsbau (FLL) organisation distinguishes three types of green roofs.
This non-profit organisation was founded in 1975 by eight professional bodies. The FLL gives advice on the technical and the practical aspects on green roofs.
The FLL uses the follwoing criteria:
- intended use
- construction
- level of maintenance
Intensive green roofs
- is comparable to that of a normal garden, hence the name ‘rooftop garden’
- easily accessible and possibility for recreational use
- widespread choice of vegetation : choice between lawn/hedges/bushes/trees
- it provides an appropriate drainage for a sufficient water retention and a high substrate thickness with a possibility for footpaths
- requires a lot of maintenance: irrigation, fertilization, mowing, ...
- greatest structural requirements
- the most expensive solution, both for construction costs as for maintenance
Simple – intensive green roofs
- less accessible and has rather a aesthetical purpose
- widespread choice of vegetation : choice between grasses/herbs/shrubs
- lower mainenance requirements nevertheless irrigation, fertilization and mowing are needed
- lower structural requirements than those of an intensive green roof
- cheaper than intensive roofs, but more expensive than extensive ones
Extensive green roofs
- acces usually restricted to maintenance only
- less choice of vegetation: only moss/sedum/herbs
- requires only minimal maintenance. No additional irrigation necessaryn only after installation
- lowest structural demands because of it’s light-weight
- the cheapest solution : the percentage of the installation cost for the green roof compared to the total investment will decrease when the size of the green roof increases
- easiliy designed
The existence of mixed types makes them sometimes difficult to dinstinguish.
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Extensive green roofs - inspection and maintenance
Reminder: an extensive vegetation does support regular entry! It’ isn’t the right place for children to play or to take a sunbath!
All types of green roofs require maintenance. Unlike other types, extensive green roofs require very little maintenance. This does not mean that no maintenance is required at all. In its first year, extensive landscaping should preferably be inspected every three months. Thereafter one inspection per year is sufficient.
The following points should be performed :
- removing parasitic plants by the root
- sowing bare areas strinking cuttings
- checking erosion formation in the substrate
- removing general pollution, including heaps of dead leaves
- replacing plants mats who may have shifted position
- checking all roof details
During Summer, most parasitic plants die away due to the dry conditions.
After installation the pre-cultivated vegetation mat may shrink a few centimeters in hot and dry conditions, which is inevitably. Fortunatelly the vegetation will colonize these formed joints.
The drought influences the color of the sedum vegetation, it varies from green to dark red. Their flowers may vary from white (sedum “album”) to yellow (sedum “acre”) or pink (sedum “spurium”).
By using Chives a touch of blue-purple can be added, a Cheddar pink provides pink flowers.
Long periods of intens frost provoke a less dense sedum vegetation, the already present mosses colonise these bare areas during Winter. Severe frost can evoke a mortality up to 30%. Next spring the mosses will be repeld by the vigorous sedums.
Insects instantly populate the vegetation mat, therefore the green roof is a perfect habitat for birds.
Extensive green roofs don't need irrigation under normal climatic conditions, irrigation does only makes the vegetation more vulnerable for an extended period of drought.
To preserve an abundant coverage we recommend an application of 100 g/m² organic fertilize Xeroflor XF116 during spring.
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Rooftop gardens
Rooftop garden appartain to the “intensive” types of green roofs, wich indicates differtent aspects:
- maintenance: during Summer rooftop gardens require regular irrigation, even up to three times a week with lawns. An intensive green roofs needs a variety a maintenance activities: pruning, mowing, ...
- roofload: rooftop gardens require 15 to 35cm substrate and more. This brings an extra load form 250kg to 600kg. This extra load makes the installation of intensive green roof on existing buildingnearly impossible because the building structure must be able to bear this weight. The installation of these gardens requires a large volume of material wich requires severe efforts.
- costs: one has to consider the investment at startup and the maintenance costs.
Nevertheless, intensive green roofs provide 2 benefits compared to extenisve green roofs:
- the architect (mostly a landscape architect) has a lot more possibilities to create an aesthetical design.
- if lawns are installed, these roofs can be used as it was a ‘real’ garden.
Traditional structural building:
- suited deck (mostly concrete)
- insulation (with a vapour barrier when needed)
- root resistant waterproofing (when non-root resisant waterproofing is applied, a PE-film is needed)
- protective layer (e.g. a thick geotextile) to portect the waterproofing from mechanical damage
- drainage layer
- substrate layer
- vegetation
Sometimes: an anchor layer of anchor system, iirgation system, ....
De Boer Green Solutions can provide you the geotextile, drainage layer and substrate.
Local nurseries provide the plants (chosen by the landscape architect) and our gardners will care for the planting.
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