The green roof market in Belgium

The greening of a roof or Horizontal Planted Complex Wall (HPCW) can be defined as the installation of a set of materials and plants composing a microflora with a water drainage system The installation of green roofs must be compatible with the existing roof structure (slab...) and the existing materials (concrete, wood...). The technique was developed in architecture in the 1970s, mainly in Scandinavian countries, Germany, Switzerland and more recently in France and Belgium in the 1990s and 2000s.

The composition of the different layers of substrate, filtration and drainage that make up the green roofs are essential. A layer of special EPDM plastic sheeting (with anti-root felt if necessary) or non-metallic welded or glued waterproofing elements separate the supporting roof structure from the substrate and drainage layer of the green roof.

There are several types of PCVH (intensive, extensive, semi-extensive...) and several installation systems: pre-vegetated sedum mats, pre-vegetated nesting sedum boxes, automatic watering systems...

In general, the installation of green roofs is more suitable for new buildings, but the greening of existing roofs is possible. As far as the maintenance and upkeep costs of green roofs are very low, especially for extensive roofs (low layer thickness and permanent vegetation cover) Green roofs are said to be much more waterproof than traditional roofs, thus increasing the durability of the roof. But the installation of environmental roofs, if poorly planned or executed, can lead to overloading of the building structure and cause damage up to the collapse of the roof.

In spite of a rather low penetration rate today, green roofs produce interesting effects (heat reduction, water filtration, pollution control, etc.), particularly in tropical areas, and could experience a stronger growth in these regions (South America, South-East Asia, Equatorial Africa). Brazil, Malaysia, Indonesia, India and China could also drive the global growth of green roofs. In particular, the Asian region will be one of the most demanded regions for green roofs by 2026, especially to curb pollution and environmental problems in large cities.

Thus, the current limitation of green roofs is that to achieve a significant environmental impact they must have a much higher penetration rate than at present and cover large areas.

The Belgian market is still very underdeveloped compared to some of its European neighbours, but it is not lacking in potential, due to a high urban concentration on its territory and growing support from governmental and municipal entities.