Vegetation technology

Local conditions

For successful establishment and long lasting vegetation it is crucial to consider the local conditions. The vegetation layer and plant communities can be modified according to site conditions; whereas, the roof height and roof slope and the predominant climate are fixed. Additional considerations include: wind exposure, air pollution, variation of temperature as well as local light and moisture conditions. Even on one roof various microclimatic conditions can occur.

Desired Green Roof type

Extensive Green Roof, Semi Intensive Green Roof, Intensive Green Roof

Green Roof System build-upGreen Roof System build-up

A professional system build-up provides a growing environment on the roof which adequately compensates for the plant's natural environment. It ensures reliable technical and ecological functionality for decades. Green Roof system build-ups contain the following functional layers: root barrier, protection layer, drainage layer, filter layer, growing medium and plant level. In
cases of chemical incompatibility, separation or slip sheets are used to keep the waterproofing and Green Roof build-ups separated. Quality criteria and testing methods for the materials can be found in the German Standard "FLL-Green Roof Guideline".

Note: Multi-Layer Green Roof build-ups ensure ecological functions, such as, water retention, biological diversity and improvement of microclimate on a large scale. In special cases (e.g. on roofs with low load bearing capacities) single layer Green Roof build-ups with a height of at least 60 mm (2.5 in) can be installed. Further prerequisites for a single layer Green Roof build-up are: sufficient roof slope, system substrates with fewer small particles as well as drainage systems which prevent pooling water.

Plant Selection

The plant selection depends on the growing medium as well as local conditions, available maintenance and the desired appearance. Low maintenance, durable and drought resistant plants are used for Extensive Green Roofs, versus, a nearly limitless plant selection for Intensive Green Roofs.

Different types of plantingDifferent types of planting

There are four different ways of planting: seed sowing, cuttings (Sedum varieties), root ball plants and pre-cultivated vegetation mats. The German Standard "FLL Green Roof Guideline" specifies the amount of seeds, cuttings, plants or mats needed for the Green Roof. The recommended planting period is in early spring (April-June) and late summer (September). For planting during the summer it is important to provide enough water to compensate for periods of low precipitation. In late autumn cold days may lead to damage of the plants due to frost. Pre-cultivated plants should be stress resistant; if not, higher maintenance is required in terms of irrigation and fertilization.

Maintenance and supportMaintenance and support

To ensure the long term aesthetic and functionality of the Green Roof it is important to provide maintenance measures. There are three stages of maintenance concerning the vegetation:

Water retentionWater retention

Due to the high water retention capacity and the delay of water run-off, Green Roofs reduce the amount of water flowing into the sewerage system and sewage plants. The amount of water retained depends on the maximum water retention capacity, the permeability and the height of the Green Roof system build-up. The water run-off coefficient specifies the amount of water retained by the Green Roof in relation to the total amount of rainwater and the water run-off. The water run-off coefficient is important in the case of municipal subsidies and for the introduction of divided storm-water taxes.

Costs/ subsidies

The cost required for a Green Roof is dependent on various factors. The type of Green Roof (e.g. extensive vs. intensive), Green Roof system build-up and different types of planting are the main factors. The logistic aspects and transportation of materials as well as the roof slope and the entire roof size are also very important. Some communities support Green Roofs with financial subsidies.