27 Mar 2019

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Green and passive roofs

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Green roofs: aesthetic and ecological benefits

Green roofs: aesthetic and ecological benefits

The construction of green roofs interests more and more planners ...

Green roofs are of interest to urban planners and building owners alike. The cost of the life cycle of the equipment reveals that the installation of a green roof is as or less expensive than that of a traditional roof. However, this investment has many social, environmental and economic benefits.

These benefits include energy efficiency (summer air conditioning and superior winter insulation), superior membrane life, sound insulation, and the ability to transform unused roofing into various types of airfields. relaxation for the occupants of a building. Green roofs filter particles out of the air, retain and clean rainwater and provide new opportunities for preserving biodiversity.

For the record, green roofs are not a new phenomenon. On the contrary, it is a standard construction method that many countries have adopted for hundreds and even thousands of years for the excellent insulating qualities of layers of soil and vegetation. In the cold climates of Iceland and Scandinavia, grass roofs help keep buildings warm, while in warmer climates like Tanzania, they help keep them cool.

On the other hand, the architects Le Corbusier and Frank Lloyd Wright were two ardent modern advocates of green roof technology, primarily because they appreciated their aesthetic qualities.

Extensive or intensive vegetation

There are two main types of green roof. The simplest to implement is the green roof covered with extensive vegetation. Extensive green roofs are rarely accessible on a daily basis. The substrate, usually a mineral soil composed of sand, gravel, crushed bricks, expanded clay pellets, peat, organic matter and a little soil, is placed on a very thin order of a few tens of millimeters. Since the substrate is shallow and many roofs reproduce the extreme conditions of the deserts, the plants must be of low height, native and rustic, from alpine or arid environments.

This type of roof does not require any water or fertilizer, and after the first year, maintenance consists of two annual visits to weed invasive species and conduct safety inspections of the insulating membrane. In summary, the four main features of this extensive facility are light weight, low capital cost, low vegetation diversity and minimal maintenance.

The other type is the roof-garden covered with intensive vegetation. It is a roof landscaped in green space, whose vegetation requires a specific and regular maintenance. This vegetation requires a special design of the roof and its supporting structure. It requires, in fact, to implement a thick layer of earth. Due to the higher soil depth (20 to 60 cm), the choice of plants is varied and may include trees and shrubs, hence the development of a more complex ecosystem. Often accessible, the intensive green roof allows various functions: recreation, green space, kitchen garden ... However, it requires more complex and costly implementation.

Thermal and acoustic insulation

We said it from the beginning, this type of installation, extensive or intensive, has many advantages. Thus, in some areas limited in green space, you can turn a view on a sealed surface into a view of a planted surface. Thanks to this type of roofing, the percentage of green spaces in the cities increases, with consequent positive effects on the air quality and the development of the animal and vegetable biotope.

During heavy rain or thunderstorms, water falling on a conventional flat roof is immediately evacuated to the drains and almost completely discharged to the sewers. In the case of a green roof, there is a buffer effect. Part of the water is consumed by plants and another is released into the atmosphere by evapotranspiration. This water does not reach the drainage network. Above all, the green roof offers a significant increase in thermal and acoustic comfort for the occupants of the building. While a roof membrane can reach a surface temperature of 65 ° C, the same membrane covered with plants remains at a temperature of 15 to 20 ° C. The vegetated earth allows reductions in temperature variations up to 40% and is one of the best acoustic insulators.

Only downside, the green roof has the major drawback that in case of leak tightness is not accessible. The greatest care is therefore to be given to the realization of it to enjoy for many years a quality green roof.

toits verts toits végétaux toits végétalisés toit de gazon végétation extensive végétation intensive

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