25.11.10

Green Roof and its advatages


Since the previous post brought up the green roof, I thought it would be appropriate to develop and explain a little bit more about the green roofing system and all its advantages. 

A green roof is a living surface of plants growing in a soil layer on top of the roof. It is constructed of many different layer on top of each other, to both protect the roof and to give a nurturing layer of soil for the plants to grow on. See here in the diagram how it could be built up:
 

 

There is 2 different basic versions of a green roof:
- Extensive on based on a very thin layer of soil which mean not alot of plants can grow here but it also means that very little maintenance is necessary.
- Intensive on the other hand has a much thicker layer of soil and can look like an ordinary garden, with trees and many different plants. But just like a garden, it needs more maintenance. This version can also only be constructed on a roof that can bear the heavy load.

This way of using vegetation on the roofs are, as you might know, not a modern invention. This a long traditional way of building in many places. But this green roofs you see in modern buildings today are very different from the traditional ones seen in the country side. This is mainly due to the different purposes and materials available nowadays. The main objective in the traditional green roofing was to use the turf as insulation and also to stop the waterproofing layer (which was mostly birch bark) from blowing away. Today the objectives are mainly environmental, economical and to improve storm water management, health and aesthetics in the community.

Advantages of Green Roofs:
Energy and economy

Cooling effects - a normal black roof can easily reach temperatures of up to80 degrees Celsius in the summer. When a soil layer and the shading plants protect the roof, the surface temperature usually doesn't rise above the surrounding air temperature.
- plants and soil evaporate water, creating a cooling effect and a moister air

Insulation and reduced wind chill
- in the winter the soil layer provides additional insulation, especially the intensive version of green roofs.

Life expectancy of the roof membrane
- The green rood protects the waterproofing layer on the roof from both the uv-light and the temperature extremes, increasing the life expectancy of the membrane from about 25 years to at least 60 years. So we save materials, energy and money and produce less waste, by using less then half of the amount of roofing materials.


Solar energy- there is no need to choose one or the other, there seems to be a postive effect both on the efficiency of the photovoltaics and on the biodiversity when roof vegitation and solar panels share the same roof. Bio diversity benefits from the patches of shade and sun provided by the panels, creating a mosaic of different mricoclimates. The photovoltaics, on the other hand, seem to benefit from the lower surrounding temperetures over the vegetation, as opposed to the normal black roof.

Storm water

Green roofs - One of the most important effects of green roofs in the cities is their potential for retaining and delaying rainwater during storms. The gutters and sewers in the city have to be big enough to cope with the amounts of water that falls during extreme storm events. As more and more surfaces in the built up areas are made hard and impermeable, less water can percolate naturally into the soil. This means that the sewers and treatment plants get higher and higher loads.
On average, an extensive green roof of 5 cm thickness, has been shown to take up 50% of the annual rainfall and evaporate it to the air.


Health and the Environment

The Heat Island Effect - the heat island effect, which makes the average temperature higher than in the country side, is becoming a big problem for peoples health and also an economic issue. All the concrete and stone and asphalt in a city absorbers the heat during day time and releases the heat during the night. The warm air also rise over the city, so that cooler air is being sucked in from the outer areas towards the center. Unfortunately, the outer areas of a city is usually filled with motorways and industrial areas, which means that the cooler air getting sucked in is very polluted.
The green roof can help to avoid this problem, with stopping the hard surfaces from absorbing so much heat by shade and also by transpire moisture into the air, which helps to cool the air down. All plants added to the city will help to improve the local climate.


Noise - the constant traffic noise echo against everything hard, like buildings and paved surfaces which leads to the noise echoing back and forth and never getting absorbed. A soft surface, like a green roof or a vertical garden mutes the noise instead of reflecting it back and forth.

Dust, pollution and the increased greenhouse effect -  dust particles, including heavy metals and other pollutants that circulate in the air to some extent get trapped in the green roofs and stays there in the substrate rather than disturbing our respiration or getting washed into the ground water.
The biggest global climate issue of our time is the increased greenhouse effect. This is the global warming that is caused by carbon dioxide (CO2) and some other gasses, such as ozone (O3), that when they reach the upper layers of the atmosphere traps the heat from the sun, keeping the earth warm. Human activities have in the past 150 years or so increased the amount of CO2 in the atmosphere, with negative effects on our entire global climate.
Green roof vegetation, as well as other vegetations, use CO2 for their respiration, and therefore reduce the negative effects of pollution. This is not a method that can be used as an only solution to the problems of pollution and global warming, but together with all the other beneficial effects of green roofs, it is a small step in the right direction.


Ecology 
- a green roof are also to a great importance to the animal life in the cities. The green roofs can contribute to a greater biodiversity and habitats like ruderal land can quiet easily be replicated on roofs together with its often endangered invertebrates as well as some bird life. 

angered invertebrates as well as some bird life.

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