Vegetated Roofs Habitat, Advantages, Disadvantages
In France, the vegetated roof is only beginning to appear in particular in the High Environmental Quality buildings.
It is an ecological, technical solution with very interesting thermal and acoustic performances, even for individual houses and additional advantages: they offer beautiful aesthetic qualities.
- History of Vegetated Roofs
Vegetated roofs are alternatives to traditional roofs and are truly ecological processes. The construction of vegetable roofs has characterized the popular architecture of many parts of the globe for centuries. The herbage roofing principle used for millennia in the Palearctic is still part of the North American Indian tradition. Even military architecture borrowed these techniques in a camouflage role by using land and vegetation to cover buildings deemed strategic.
Many European countries have adopted. Vegetated roofs are found mainly in Switzerland, North America, the Netherlands, the Scandinavian countries, and Japan. In these various countries, these vegetated roofs are widespread and even encouraged in Germany*.
* In Germany, 13 million square meters of the vegetated roof is laid each year. In France, according to the CSTB, 200,000 square meters are installed per year. The market is expected to grow by 15-20% per year as a result of the proliferation of HQE projects.
A mixture of soil and rooted herbaceous plants made it possible to build relatively well-insulated roofs made from materials readily available locally. These roofs were air and watertight, resistant to wind and fire. These heavy roofs required strong frames and the addition of a protective layer placed between the vegetated part and the frame so that the latter did not rot. Wood tiles or unworn birch bark plates were generally used. The current construction uses special plastic tarpaulins (with Root felt) or sealed thermo-welded or bonded non-metallic elements.
There are three types of vegetated roofs: extensive, semi-intensive, and intensive. Picbleu Photo.
- The Three Types of Vegetated Roofs
Many rooftops in terraces, canopies, or garages shelters are left bare and barren while they could easily be vegetated and transformed into gardens, for our greatest pleasure and the greatest good of the planet. If intensive vegetation requires the intervention of professionals, the so-called extensive vegetation, of more natural type, is available to all.
Private individuals can vegetate themselves small roofs in Terrace or slightly inclined. The different techniques, the choice of substrates and plants, as well as the maintenance questions, are discussed in detail. Recent technical developments, lower installation costs, and low maintenance requirements now allow a strong development of legalization to be envisaged.
Depending on the substrate thickness and the type of vegetation used, there are three types of vegetated roofs: extensive, semi-intensive, and intensive.
- The extensive greening
Extensive revegetation consists in creating an ecosystem on a low-thickness cultivated complex (3 to 7 cm approximately), allowing the realization of a permanent vegetation cover. This thinness prevents the appearance of water-intensive grasses, which would stifle seams. In addition to the low roof weight (30 to 100 kg/m2 with water saturation), its main advantage is that it does not require maintenance or watering except in case of prolonged dryness. It is well suited to large areas, inclined roofs, and existing homes. The only drawback is that these roofs cannot be cultivated or trampled. The investment is modest (from 30 to 50 € HT / m2 depending on the method of cultivation).
- Semi-intensive vegetation
The semi-intensive vegetalization uses an elaborate Culture Complex, of medium thickness (15 cm). With a decorative purpose and reduced maintenance, it will require regular watering (usually a drip). This type of cultivation can mix curfews, plants with flowers or foliage, vegetables, and even small shrubs or vines such as the Virgin vine or honeysuckle. The substrate of a semi-extensive culture is usually composed of about 50% porous aggregates.
- Intensive revegetation
The intensive legalization is a veritable roof terrace garden, recommended for small and medium areas. Cultivation takes place in bins up to 1 or 2 meters deep. As the substrate is thicker (about 15 to 30 cm thick), it is possible to plant grasses, grass, perennials or ornamental shrubs. The volume of aggregates is often reduced to 40% to make room for more nutrients.
The necessary condition for this type of revegetation is the requirement to have a roof capable of supporting an overload weight of 120 to 350 kg/m2 when it is saturated with water during periods of intense precipitation.
In the case of actual hanging gardens, the load weight must be carefully calculated by a design office to guard against the risk of structural collapse. Maintenance for this type of roof with intensive vegetation is more demanding (mowing and pruning, manure, regular watering). A huge advantage is that of the pleasure garden; it is possible to walk there. The initial investment is much higher.
These characteristics make it possible to predict a good future in France of the vegetated roof.