Vegetable roofs, also known as green roofs, are those cover surfaces, totally or partially occupied by vegetation.
They were born thousands of years ago, and among the most famous are the Hanging Gardens of Babylon, considered one of the seven wonders of the ancient world, in which trees and plants were planted on the blocks and stone walls waterproofed with reeds and pitch.
Hanging Gardens of Babylon
Centuries later, a practice began in Iceland in the construction of houses in which the roofs were covered with grass and the thick walls were interspersed grass blades between the layers of stone. With this method thermal insulation was achieved, making the houses warm in winter and cool in summer. This system became popular throughout Scandinavia.
The same technique has also been used in warm countries such as Tanzania, in this case, to protect houses from heat.
Vidimyri church, Iceland. Built in 1834.
Modern green roofs have their origin in Germany, where they have been installed since the 1960s and constitute, in general, an important architectural element.
Other countries that have been implementing this technique are the United States, the United Kingdom, Switzerland, Austria, Japan, etc. There are even government regulations or financial aid to favor development in some of them.
The Waldspirale Darmstadt Germany.
Without going any further, last September, the city of Copenhagen (Denmark), characteristic of being a pioneer in eco-sustainable issues, decided to implement a law whereby the owners of new roofs must have some type of vegetation in them. This law is intended to improve the habitat and reduce energy consumption. There are also plans to cover the old roofs of the city with vegetation in order to become carbon neutral in 2025.
It is the second city in the world with such legislation, since in Toronto (Canada), it was approved by the City Council in 2009 and is being applied since the beginning of 2010 in all new buildings whose surface area exceeds 2,000 m2 and whose use is residential, commercial or institutional. As of 2012 it is also applied in industrial constructions.
The great success of plant coverings lies in the wide variety of benefits they provide.
They extend the life of the roof, acting as a protective layer. As the substrate and plants absorb in rainwater the runoff is reduced, and thus the risk of flooding. They filter air pollutants, carbon dioxide, heavy metals and water pollutants. Improve the energy efficiency of the building. The roof withstands large thermal fluctuations and solar radiation, and the last floors of the building are subject to higher temperatures, in hot times, and at lower temperatures, in winter, than the rest of the building. The plant cover offers protection against solar radiation and, thanks to the thermal inertia of the earth, it has a damping effect on the temperature, thus reducing the entry and exit of energy through the plant cover. This effect produces an increase in comfort conditions and, in the long term, energy savings by air conditioning. They suppose an acoustic barrier, since the substrate isolates the low frequency sounds, and the vegetal tapestry the high frequency sounds. They can become a recreation and cultivation space for fruits, vegetables, flowers, etc. They improve the aesthetics of the building. They can be a passage zone or habitat for birds and microfauna, thus enriching and protecting the biodiversity of urban areas, improving their environmental conditions and generating a naturalized space.
Rooftop Garden Restaurant. Nueva York.
Generalmente las cubiertas vegetales se clasifican en dos categorías.
Extensivas. Son cubiertas que requieren un mantenimiento mínimo. La capa de sustrato es poco profunda y las especies vegetales utilizadas son musgos, herbáceas y crasas tipo Sedum, resistentes a condiciones climáticas duras.
Generan poca biomasa, así que se pueden instalar en edificios rehabilitados, ya que no suponen una carga adicional importante para la estructura.
Extensive cover at Nanyang Technological University. Singapore.
Intensive They are covered in which large plants are grown, and even small trees, being able to constitute true gardens on the terraces of the buildings. They require regular maintenance, fertilization, irrigation, pruning, etc. As they require a substrate of great thickness (minimum 152 mm), they are usually made in new buildings, whose structure has been designed to support the weight of all elements.
Brooklyn grange. NY.
A vegetative cover is formed by several layers of different materials, each of which is placed for a specific purpose. The following components are placed from the roof slab facing up.
Waterproofing membrane. It can be made from bituminous materials, with a certain recycled content, such as products made from polyethylene or EPDM synthetic rubber.
Sometimes, the waterproof membrane incorporates an anti-root treatment, especially in the case of intensive covers, where radical systems are more aggressive. This treatment can consist of a high density polyethylene or modified asphalt membrane reinforced with polyester and ceramic granules, it can also consist of copper or arsenic additives in the waterproofing membrane.
Isolation. It is usually made of extruded polystyrene, which in addition to its insulating properties has great resistance to water penetration. Water retention and drainage. It is a system designed to store water, for the supply of plants in times without rain, while ensuring good drainage and aeration, so that it ensures a good balance between water and air.
The system can be made with recycled polypropylene fibers or with recycled polyethylene panels. It can retain water and nutrients to be used later by the substrate located on it, which the roots of the plants reach by evaporation or by direct contact.
This layer has holes that allow air circulation, evaporation of moisture and ventilation of soil and roots.
In other systems, the drainage layer is formed by perforated polystyrene plates, some porous material or gravel, and its function is to improve drainage control, although it does not have the ability to retain water. If you want to store water, you can place raised slabs on supports. In the space that remains between the slabs and the waterproofing, rainwater that filters through the draining surface is stored. This system is known as cistern cover.
Filter. It prevents the substrate from falling on the drain and plugging it. It can be a geotextile polyester fiber material. Substratum. In addition to being the support of the vegetation on the entire surface of the roof, it is a growth medium designed to achieve optimum water retention, permeability, aeration capacity and erosion resistance. Plants. The plants chosen for the roof must be resistant to the climatic conditions of the place, act as upholsteries and do not need much maintenance, especially in extensive systems.
They should be perennial to keep the green cover all year. In general, annual or lively plants are not favorable, since, as they must reproduce each year, germination will condition the coverage, and for half a year nothing will grow on the cover.
In extensive systems, plants should have a shallow radical system. Succulents are usually planted such as those of the Sedum genus, mosses, lichens, native herbaceous plants and plants of dry climates.
In intensive systems there are not so many limitations, and vegetation of all kinds can be included: different herbaceous plants, grass, vines, shrubs and small evergreens.
Components of a vegetation cover.
It should be noted that, since plant coverings began to be installed, numerous representative buildings in various cities around the world today have their own green roofs, many of which contain indigenous plants declared vulnerable or endangered, then serving these roofs as a biodiversity reservoir.
In Switzerland there is one of the oldest green roofs in Europe, it is in the water purification plant of Lake Moos, near Zurich, which was built in 1913. During the first summer the plant was operational, temperatures were very high, and the water contained in the tanks was contaminated with bacteria. To solve the problem of contamination, it was concluded that the tanks had to be cooled during the summer season, therefore, a layer of soil from the surrounding meadows was spread on the deck and under this, another gravel to enable drainage. This land contained seeds of native flowers and herbs, which germinated and made the cover one of the largest green roofs in Europe. It currently contains 175 species of higher plants, many of which are rare and are endangered locally and nationally.
Water purification plant of Lake Moos. Switzerland.
In France there is a huge green roof of 8,000 m2 that has been incorporated into the new L’Historial de la Vendée museum that opened in June 2006 in Les Lucs-sur-Boulogne. The museum’s roof consists of triangular facets whose angles are large enough in relation to the building to maintain an expressiveness that distinguishes it from the natural terrain. The triangulated relief of the green roof and its large overhangs protect the exhibition halls from the sun, improving the conservation of the exposed materials.
L’Historial de la Vendé Museum, France.
The new building of the Renzo Piano California Academy of Sciences, located in the Golden Gate Park of San Francisco, has a green roof of one hectare of native vegetation, designed to protect some local endangered species. It is covered with 1.7 million native plants and with the undulating shape simulating that of the San Francisco hills. This “living roof” fulfills the function of keeping the interior of the building cool and at the same time collecting about 13 million liters of water per year that is largely reused for museum use.
California Academy of Sciences. San Francisco.
The Leed Platinum Vancouver Convention Center, opened in 1986 and expanded in 2010 for the Winter Olympics, has the largest green roof in Canada. It has a cover of 5 acres (20,234 m2) landscaped with more than 400,000 native plants, providing a natural habitat for birds, small mammals and insects in the area.
Vancouver Convention Center Canada.
The greatest demand for specialty products for the creation of roof and roof gardens has been and is a trend in gardening in recent times, since in large cities it is sometimes difficult to have new spaces for gardening. Therefore, the possibility of landscaping on terraces, covered with buildings, patios and roofs is an option that favors the increase of urban green areas.
The numerous advantages of green roofs make them a growing preference, and the planning and creation of this type of green space is increasingly in the minds of a large group of professionals in the field of gardening, landscaping, the architecture and the environment, constituting an interesting job opportunity and with a future.
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