Green Roofs: Urban Environmental Transformation

World population which is 6. 7 billion now is expected to reach 9 billion in another 40 years time. In the mean time it is also expected with the standard of living improving every where the increase in population will cause the demand for energy to grow by a factor of two. Hence the search for new sources of fuel to meet these needs is already on. The area that needs our attention is improving the efficiency of energy usage.

There is a need to use available technology to improve crop yields, to improve process efficiencies for producing manufactured goods at lower costs and also to provide better insulation for buildings to reduce energy losses.

A focused approach in improving energy efficiency can give long lasting benefit in energy conservation which can reduce the pressure on additional energy needs. A focused approach can yield results has been demonstrated by Germany where the green house emissions have reduced by 18 percent during the 15 year period from 1990 to 2005 while it has gone up by 16 percent in the same period in the United States .

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Germany has more than 13 million square meters of green roof systems as of 2002 and Tokyo has already mandated in 2001 that at least 20 percent of the roof area that is larger than 1000 square meters should be cultivated . Chicago and Washington DC are the leading cities in United States that have gone for green roofs in a big way. Now Toronto is the latest city to join this trend. Green roof and its advantages Green roof is an option that is considered while we think of energy efficiency in buildings.

It is proposed to use green roof in place of the traditional roof.

Green roof is a living system consisting of soil along with compost and vegetation. It can act as an effective insulation that can lower the inside temperature in summer months and at the same time help in retaining the essential heat in winter months. It will be quite effective in reducing the energy consumption of the building by 25 percent on a conservative estimate. As more buildings get covered with green roofs the peak period cooling required in summer can get reduced and in turn this can reduce the CO2 emissions from power plants . It provides protection from UV light degrading the roof top.

The fluctuations in day-night temperatures are also reduced. In a study it has been shown that the temperature fluctuations that are as much as 50 degrees C has been reduced to 3 degrees C. The normal life span of a black roof that is 10 years can be increased to as much as 30 years by going for a green roof. There are reports from Germany that there are green roofs that have completed 50 years. It has other benefits too. It can relieve the pressure on storm water drain pipes. It is capable of retaining as much as 50 percent of the rain water that falls on it. In addition it can slow down the remaining rain water.

This happens because the media has to get saturated before the excess water is released. The green roof can delay this process by 95 min to 4 hours . Such an environmental approach for storm water drain can reduce the size of the drain pipe that is needed otherwise . In summer months all the rain water is expected to be absorbed by the green roof while in winter it may be restricted to 20 percent only. The effect of the heat island that is experienced in all major cities due to the impermeable surfaces such as buildings, roads and parking lots can get reduced due to the cooling effect provided by the vegetation on building tops.

Such heat islands are known to increase the temperature in business districts by as much as 10 degree Fahrenheit above the surrounding land. If all the building in the city are converted to green roofs, it will be possible to eliminate this temperature difference. It has the capability to re-oxygenate the air and improve air quality by filtering dust and smog particles. In urban centers where green space is negligible the introduction of green roofs can provide psychological benefit to the urban population as human beings are known to be more comfortable with natural settings.

Such an environmental change can help workers to concentrate on their jobs leading to job satisfaction and improved productivity . Green roof provides new opportunities in design of architecture. The green roof can help in the building to merge in the landscape and provide aesthetic improvement. It can provide shelter to butterflies and birds and help in habitat preservation. The Ducks Unlimited living roof in north of Winnipeg, Canada has become indistinguishable from the surrounding marshes when one looks down from the air. It was built in 1992.

Many species of insects along with birds and ducks have made their home in this green roof . Green roof has the advantage of reducing noise levels. It reduces sound reflection and also improves sound insulation. It can help in reducing the noise levels inside buildings that are closer to airports and industrial parks. A green roof substrate of 12mm thickness is capable of providing noise reduction of 40 db . It is learnt that nearly 30 percent of nitrogen and phosphorus that gets released in streams is from building roof tops where they are accumulated. Green roof can act as a bio-filter and reduce this water contamination.

Hence it can improve water quality . Green roofs are being used for growing agricultural products. People are growing vegetables in roof gardens. It can provide fresh vegetables for home use or for commercial use too. A bar owner in Washington DC has plans to grow tomatoes and chilies on the roof top for his use in the bar, this summer . Green roof systems The soil content, the growth medium and the types of plants used differ in the system of green roof whether it is intensive, semi-intensive or extensive. Among the three systems extensive system is the least dense.

The soil and the growth medium used here are less than 6 inches in thickness. Mosses and small shrubs that can withstand harsh weather conditions of high winds and drought find a place in this system. The need for weeding once a year is considered during designing such a system. These are generally low weight bearing. It is self sustaining and requires very little maintenance. The intensive system requires 10 inches or more in soil and growth material which consists of several layers. A full garden with several trees and plants can be accommodated in such a system. This can have more plant variety.

As the plant density is going to be high the need for watering and monitoring for stray seedlings is going to be equally high. It is intensive because it is labor intensive due to the requirement of irrigation and other maintenance needs. The semi-intensive system utilizes soil and growth medium that is with in 6 to 10 inches in thickness. As the name suggests, this system is less complex than the intensive system but at the same time more intense than the extensive system. The types of vegetation that are used in such a system are some evergreens, small shrubs and also grasses .

It is recommended to choose mature vegetation which covers 95 percent of the soil because it needs very little maintenance. The plants are to chosen in such a way that they get acclimatized easily to the environment. Green roof by-law A green roof by-law was passed in the city of Toronto in May 2008 where it has become mandatory to have green roof on all new buildings. A new building where the floor space is going to be more than 2000 square meters has to make provision for 20 to 60 percent of the roof to have vegetation. This by-law is applicable to both commercial as well as residential buildings.

Toronto is the first North American city that has passed such a law . A Green roof construction standard has been published which lists the minimum requirements to meet the Ontario building code needs. It covers all issues associated with the green roof. The structural standards required for green roofs are more stringent. It may not be possible to accommodate the green roof on some of the old buildings due to weight load factor. The green roof also requires better water proofing of the roof to avoid leakages. There is a possibility of plant roots getting through the waterproof membrane. Available technology

The green roof systems are available in three forms • Complete system – Different components that are part of the system are integrated and are available as a composite system. • Modular system – This consists of a tray of vegetation which is grown off site. The trays can be placed on the roof to cover the whole area. The trays have different depths growing medium starting from 3 inches to 12 inches. This has the advantage of removing the trays easily in case of any problem associated with roofing substance. • Blankets of pre-cultivated vegetation to be rolled on the roof along with the drainage mats.

This has a thickness that is less than 2 inches. Conclusions The urban environment has degraded over the years. Population explosion and migration to urban centers have caused ecological imbalance and irreparable damage. Green roof tops can have a positive impact on the overall life of the citizen. There is a need to educate the people and make them willing partners in green roof for its success. The lack of technical information on green roofs and how to build them is coming in the way of faster implementation of this technology in many places.

Many cities all over the world are providing incentives to builders to include green roofs in their building plans so that individuals as well as society at large can enjoy the benefits from its implementation. Even though the initial costs are high in comparison with the conventional roofs, once implemented it can provide long term cost benefits in energy costs alone leaving aside all other indirect benefits. It is high time that people living in other countries realize the importance of environmental conservation lessons learnt in Germany and implement them and enjoy the long term benefits from them.

It can also help in addressing food security issues.

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