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Maintenance of extensive green roofs

Extensive green roofs need to work as an eco-system in their own right, which has the advantage of reducing the amount of maintenance needed on the vegetation. However, this minimum amount of maintenance remains absolutely indispensable to control the development of the plants.

The aim of the maintenance is to achieve or preserve vegetation cover of 80% or more, to control the development of weed species, to ensure the sustained development of the plants chosen. It usually consists of cleaning the rainwater inlets, removing detritus deposited by the wind, putting the growing medium back into place if it has been moved by the wind, manual weeding, replanting any areas where there is no vegetation and adding fertiliser if it is deemed necessary after inspecting the roof. In the specific case of grass-based green roofs, it will also be necessary to mow the surface. For roofs equipped with an automatic irrigation system (where recommended by the designer of the green roof system in certain geographical areas), it will also need to be maintained and drained in winter.

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After installing the system, according to the CSFE Professional Rules there are 2 maintenance periods for green roofs, which are:

1- Establishment period: period of maintenance necessary after installation of the system on the roof to obtain at least 80% coverage. This varies according to how the vegetation is installed (see table below - extract from the Professional Rules).

Type of green roof

Pre-grown

mats

Planted,

micro plugs,

pots

Sown

Length of establishment period

3 to 6 months

1 to 2 years

1 to 3 years

Minimum frequency of maintenance

Once - twice a  year

3 to 4 times a year

3 to 4 times a year

* if the roof is shaded

2- Routine maintenance period: this follows the establishment period and the aim is to maintain a coverage rate over 80%. The minimum frequency will be two visits a year.