Today, green roofs and living walls are becoming more and more popular in our cities, where green spaces are now less common and atmospheric pollution is on the increase.
Types of green roofs
Generally speaking, there are three types of green roof.
• Extensive green roofs, which can be established on a very thin layer of substrate and require only a minimum amount of maintenance since they consist of plants selected for their tolerance such as hardy succulents, or drought-resistant perennials and grasses.
• Intensive green roofs resemble traditional gardens and consist of a wider variety of plants, such as shrubs and trees. They can even include walkways, benches, lighting and ponds. The load-bearing capacity of the roof is very important.
• Semi-intensive green roofs seek to be both aesthetic and accessible. The primary objective is a visual effect with watering required for selected plants during periods of drought, and they require fertilizer application and regular maintenance.
Installation
A green roof system can be installed on roofs that are flat or slightly pitched For pitches of more than 30%, precise methods have to be used to ensure that erosion does not occur. Such a system usually consists of a waterproofing membrane, a drainage board or layer, a root barrier and the substrate. A capillary mat, which increases water retention in the substrate, and layers of insulation, can also be added to these components. Several types of materials can be used in the growing medium: lava and pumice, slag, expanded slate and clay, peat, perlite, sand and recycled materials. The depth of the substrate can vary between 5 and 50 cm, according to the type of green roof, local climatic conditions, plant species and the load-bearing capacity of the roof.
Irrigation
• Sprinkler irrigation: not recommended, because this technology is too restrictive on a roof (pressure and flow rates too high, throw, losses, run-off, required depth...).
• Surface drip irrigation: possible on extensive and intensive systems.
• Subsurface drip irrigation: possible on intensive systems. Only possible with an irrigation mat (CoverNet style).
