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Green roof
From Ekopedia
The green roof (vegetable roof, or vegetalized roof) is a roof made with a covering of topsoil on which plants are grown.
Historically, the construction of green roofs is done in a traditional way in several Scandinavian and European countries. The mixture of ground and plants rooted on the roofs made it possible to carry out roofs insulated relatively well, tight to the air and water, resistant to the wind and fire. The whole being done with materials easily available.
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[edit] Around the world
- In Germany, during the 10 last years, 10% of the roofs created were of this nature. A system of points grants a reduction of environmental tax to the property developers who use the green roofs. In Berlin for example, the city takes responsibility for its 60% expenditure related on the vegetalized roofs and the installation of water treatment of rain.
- In Japan, the city of Tokyo requires that any construction occupying more than 10.000 square feet (929m2) of ground be covered with plants on 20% of its surface.
- In the USA, the green roofs were associated a long time marginal concepts of bioclimatic architecture, hidden and covered with ground. This architecture of fallout shelter did not know a great popularity. The arrival of new lighter farming systems and the new environmental stakes started again the interest for these roofs. One speaks now about durable roofs which add a quality of life to the urban residential buildings.
- In Canada, the commercial and residential projects including green roofs are still very few (a score in Quebec), but the products and the expertise are now available and of many babies-boomers start to dream of roof-gardens and meadows flowered for their condo or their apartment of city.
- In France, the concept is almost unknown. An Austrian architect in New Zealand, Hundertwasser, developed this idea in some of his constructions.
[edit] Advantages
[edit] Environmental
By absorbing heat, the green roofs reduce the load of the apparatuses of cooling of the buildings, in addition to filtering the ambient air, eliminating the suspended particles in the air and carbon dioxide. During the episodes of strong rains, the cities have often evil to evacuate water. A sufficient surface of hanging gardens increases considerably the absorption of rainwater, which would relieve the sewerage system. Moreover, on a city scale, these green roofs can reduce the effect of small island thermal, reducing considerably the temperature of the city in summer.
[edit] Economic
A simple reduction in 1°C of the temperature of surface removes 5% of the demand for electricity for air-conditioning and the refrigeration. According to the European experiment, the green roofs last twice longer than the ordinary roofs. They can be also used for agricultural ends. Thus, the hotel Fairmount Waterfront (Toronto, Canada) cultivates grasses, flowers and vegetables on its roof garden and saves thus approximately 30.000$ EDGE per annum in purchases of food products. The implementation is rather simple as a whole, and maintenance varies according to plantations'. These vegetalized roofs play the part of insulator.
[edit] Social
The green roofs offer a good soundproofing as well as an oasis of greenery. Technology offers also possibilities of agriculture in urban environment which one could exploit to help to nourish more strapped families.
[edit] Considerations
A lot of people mixes the concept of ground roof with the green roof. The ground roof “literally” is covered with ground and generally with grass and shrubs. A ground roof it is heavy. From 75 to 100 pounds with the cubic foot (of 1150 to 1500 kg with the m3), which comes down to saying that a roof of 1200 pi2 (111m2) of surface with a covering of 12 inches (30 cm) of ground (in general one puts of them at least 6 inches and to several feet) would weigh from 45 to 60 tons! A ground roof must consequently be carried by a very powerful set of structures and cover of a solid and tight roof. It is not question of traditional structures for such a weight. Do not forget to think of the additional weight of snow (to 60 books with the square foot; 300Kg with the m2)! The ground roof must be insulated (under the ground) and a detailed attention must be brought to the drainage, because such a roof, already heavy, could not tolerate an overload of water or ice. Some of these houses will be straightforwardly under the line of ground in their entity, whereas others are embanked in north to the roof leaving the Southern half of the house open to the light. The underground house is a phenomenon generally associated the arid or semi-arid areas. Generally, more one goes up towards North, more one must forsake the house under ground and more one only goes towards the house equipped with a ground roof.
The green roof, or alive, is a Scandinavian variation of the ground roof. Attention, because the ground is not really an insulator, it protects by its mass, but does not insulate. The green roof, by its lightness and the air which is there, is, as for him, more insulator. Instead of the ground, one generally uses, one compost light whose principal element is bark, hay or straw mixed with compost and/or poor ground. That reduces the weight of the roof by 80% in comparison with a roof of ground and the poverty of the compost prevents the growth of plants other than very resistant (which die in the 1st dryness).
[edit] Techniques
[edit] Old methods
In the beginning, the green roofs was born from a simple practical question. One extended from the ground or the turfs on the bark of birch posed on the roof. The bark held the role of impermeable barrier while the purpose of the ground was only only to retain this bark.
[edit] Contemporary techniques
A green or vegetable roof is composed primarily of four components. On the basis of the support of roof, one finds:
- a seal : bituminous, rubber, polyolefin/TPO/FPO (cartouche ethylene propylene + polypropylene) PVC or EPDM.
- a layer of drainage and filtration : aggregates of clay expanded, stones, gravels, alveolate and ribbed plates of polystyrene.
- a substrate of growth : foam of sphaigne, compost, black cotton soil, compost.
- a vegetable layer : To privilege hardy perennials and indigenous very resistant to the extreme temperatures and which will be established quickly to cover surfaces of ground in order to reduce its draining by the sun and the wind. The floor coverings have also the advantage of leaving little place with bad grasses and of reducing maintenance.
[edit] The extensive type
Particularly adapted to the buildings of large surfaces, tilted roofs or already existing dwellings, for their low thickness of substrate (3 to approximately 15 cm), their weight of overload ranging between 30 and 100 kg/m ² (with maximum water capacity), their restricted maintenance (watering only in the event of prolonged dryness) and their colonizing and very resistant vegetation (foams and sédums, graminaceous, fatty plants). The height of these plants does not exceed 25 cm maximum and the mixing of several varieties gives them a multicoloured aspect varying with the liking of the seasons. Only disadvantage, this type of roof is not practicable (can neither be cultivated nor trampled).
[edit] The intensive type
- intensive or “semi type the “- intensive” (also called hanging garden). Recommended for the small ones and average surfaces. The thickness of the substrate is more important (15 to approximately 30 cm) for a weight of overload ranging between 120 and 350 kg/m ² (with maximum water capacity). Allowing to accomodate a vegetation with strong development racinaire and air of horticultural type such as graminaceous, grasses, hardy perennials or shrubs. A moderate maintenance and a regular watering are necessary. Comparable with the ordinary gardens, it is possible to sow or cultivate any kind of plants. Because of its important load, construction must be adapted. It is preferable to be addressed to professionals to check the capacity of the structures of the building before any intervention.
[edit] A new method
a flexible solution has been just marketed which can be installed on an existing terrace or a flat roof without realization of preliminary work. It consists in buying vats in the shape of truncated pyramid out of stainless steel which also assume the role of support of floor. These vats are sold already planted with extended an enough variety of trees and shrubs.
[edit] See also
[edit] Internal links
[edit] External links
- Independent green roof organisation in the UK
- leading website for self build in the UK
- G-Sky Inc. The world's leading Green Wall and Roof providers, Design, Installation, Plants, etc
- http://www.treehugger.com/files/2005/09/green_roofs_a_p.php
- May your roof be green
