Green roofs » or « rooftops garden » have existed for many years. They are designed as a set of elements covering a roof (flat or sloping) of a house or the top of a building. This design makes it possible to create a green space in various forms, from a simple green carpet to a real garden (depending on the thickness of the substrate). Unfortunately forgotten, they were rediscovered in the second half of the 20th century. Today, many people are aware of the degradation of nature. As a result, they are adopting more eco-responsible gestures such as green roofing, making this concept a new trend. We are going to look more specifically at green roofs in urban areas.
A green roof in Brussels?
First of all, it is necessary to bear in mind that the City of Brussels has no less than 350 roofs. This is therefore a potential that can be exploited in various ways. Ideas abound:
- installing photovoltaic or thermal solar panels;
- putting wind turbines on roofs ;
- to install green roofs that are favourable to biodiversity;
- to set up a vegetable garden ;
- open these spaces to the public by creating a roof terrace;
- paint the roofs in white to fight against the summer heat
- …
In urban centres, roofs and concrete surfaces such as storage areas, roads and car parks take up most of the territory. Mostly mineralised, made of non-living matter, these spaces leave no room for vegetation. Vegetation is a real gamble on the future for the well-being of humans and the environment. Indeed, green roofs have ecological virtues and are therefore part of a sustainable development approach. Therefore, against a backdrop of climate change, what could be more logical than using roofs as a growing area? It is becoming imperative to rebalance plant and mineral resources in cities. Moreover, in addition to the ecological aspect, green roofing is an alternative to tiles or slates covering your roof.
There are three types of green roofing: extensive, semi-intensive and intensive green roofing. The choice is made according to needs, budget, type of roofing and the structure of the building. Each type of roofing requires different preparation and consideration.
In addition, a subsidy is granted to residents of the city of Brussels (postal codes: 1000, 1020, 1120, 1130 Brussels) for the installation of a green roof on a building located in this territory. However, the roof must meet a series of technical criteria.
Green roofs in urban areas real added value
In a concrete urban environment, green roofs offer a green space with many environmental, economic and social benefits. This is why WAO has decided to start installing a vegetable garden roof. The interest is to make the roof a participating place, with its specific features that contribute to the environmental and health well-being of coworkers. Indeed, urban agriculture is a place of sharing and conviviality. It will enable coworkers to forge links. Moreover, using the roof as a vegetable garden provides an opening to the outside within the closed work spaces. It also provides an opportunity to « go out to the garden ». In addition to the social contribution of the vegetable garden, it is a source of (local) food and freshness. What could be better than going there to fetch a tomato for your sandwich at lunchtime?
The advantages of a ggreen roofs in urban areas
As you can see, a green roof in an urban environment has many advantages:
- It promotes biodiversity in the city
The green roofs are a refuge for the fauna in the city (insects, spiders, birds…) and participate in the « green network ».
- It offers a more pleasant urban landscape
In addition to the ecological benefits, the green roof improves the aesthetic appearance of the roof.
- It improves air quality
By absorbing dust, pollen and certain pollutants, it improves the quality of the air we breathe in cities. Thus, by bringing greenery into the urban environment, we improve the quality of the environment.
- It promotes thermal and sound insulation
It increases the thermal and acoustic protection of the house. In fact, it acts as an additional insulating layer. Therefore, the thickness of the crop reduces noise pollution.
- It allows rainwater to be retained
Vegetated roofs retain rainwater and release it more slowly, thus preventing flooding.
- It improves the microclimate
Indeed, it regulates air humidity (hygrometry) and reduces urban overheating (thus reducing heat islands in summer).
- It increases the longevity of the roof.
Green roofs have a longer lifespan because they are protected from ultraviolet radiation and extreme temperature variations. And it is these last ones that tend to deteriorate roof coverings.
- It is an alternative to gardens in a dense conurbation.
Depending on the city, roofs represent between 15 and 30% of the horizontal surface. This is an opportunity to develop green spaces, which are less and less numerous in cities. The idea is to give back to nature a small place.
Disadvantages of a vegetated roof
However, although this project seems ideal, it still has some drawbacks or challenges.
- Requires regular maintenance
It may even be weighed down by weeds that may grow. Furthermore, the installation of a watering system is necessary in some cases.
- It can represent a large monetary investment at the outset
However, costs vary greatly depending on the project.
- Roof access must be provided
- The waterproof layer does not last forever.
- In case of a leak, it is more difficult to locate and repair them.
Indeed, it will have to be changed after 30 or 50 years of use. To do so, the entire green roof will have to be removed.
In addition, there are other elements to take into account regarding the roof on which you intend to launch this project. A diagnosis of the state of the roof should be carried out beforehand.
What should be remembered about green roofs in an urban environment?
Despite the few drawbacks and challenges this initiative represents, it is a project that offers many advantages on different levels. Indeed, it meets the objectives of regulation, sustainable development in the city and much more. In addition to improving the urban landscape, it also has a positive impact on ecology. Indeed, it helps to preserve biodiversity by restoring a place for nature in the urban environment and rebalancing the plant and mineral resources. At a time when environmental problems are becoming more pressing, the green roof represents a boost to improve the situation and raise public awareness. We can all contribute to the well-being of our common host: the Earth. You can start by greening your roof.
