Green roof Technology

What is Green roof?

A green roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and drainage and irrigation systems. (The use of “green” refers to the growing trend of environmentalism and does not refer to roofs which are merely colored green, as with green roof tiles or roof shingles.)

Environmental Benefits:

Green roofs are used to:

• Reduce heating (by adding mass and thermal resistance value)
• A 2005 study by Brad Bass of the University of Toronto’s showed that green roofs can also reduce heat loss and energy consumption in winter conditions.
• Reduce cooling (by evaporative cooling) loads on a building by fifty to ninety percent.
• especially if it is glassed in so as to act as a terrarium and passive solar heat reservoir — a concentration of green roofs in an urban area can even reduce the city's average temperatures during the summer
• Reduce storm water run off — see water-wise gardening
• Natural Habitat Creation  — see urban wilderness
• Filter pollutants and carbon dioxide out of the air which helps lower disease rates such as asthma — see living wall
• Filter pollutants and heavy metals out of rainwater
• Help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies
• If installed correctly many living roofs can contribute to LEED points
• Agricultural space.

Financial Benefits:

• Increase roof life span dramatically
• Increase Real Estate Value
  

A green roof is often a key component of an autonomous building.

Several studies have been carried out in Germany since the 1970s. Berlin is one of the most important centers of green roof research in Germany. Particularly in the last 10 years, much more research has begun. About ten green roof research centers exists in the USA and activities exist in about 40 countries. In a recent study on the impacts of green infrastructure, in particular green roofs in the Greater Manchester area, researchers found that adding green roofs can help keep temperatures down, particularly in urban areas: “adding green roofs to all buildings can have a dramatic effect on maximum surface temperatures, keeping temperatures below the 1961-1990 current form case for all time periods and emissions scenarios. Roof greening makes the biggest difference…where the building proportion is high and the evaporative fraction is low. Thus, the largest difference was made in the town centers.”

Types:

Green roofs can be categorized as intensive, "semi-intensive", or extensive, depending on the depth of planting medium and the amount of maintenance they need. Traditional roof gardens, which require a reasonable depth of soil to grow large plants or conventional lawns, are considered "intensive" because they are lab our-intensive, requiring irrigation, feeding and other maintenance. Intensive roofs are more park-like with easy access and may include anything from kitchen herbs to shrubs and small trees.

"Extensive" green roofs, by contrast, are designed to be virtually self-sustaining and should require only a minimum of maintenance, perhaps a once-yearly weeding or an application of slow-release fertilizer to boost growth. Extensive roofs are usually only accessed for maintenance. They can be established on a very thin layer of "soil" (most use specially formulated composts): even a thin layer of rock wool laid directly onto a watertight roof can support a planting of Sedum species and mosses.

Another important distinction is between pitched green roofs and flat green roofs. Pitched sod roofs, a traditional feature of many Scandinavian buildings, tend to be of a simpler design than flat green roofs. This is because the pitch of the roof reduces the risk of water penetrating through the roof structure, allowing the use of fewer waterproofing and drainage layers.

History:

Green Roofs have a long history starting back centuries ago.

Modern green roofs, which are made of a system of manufactured layers deliberately placed over roofs to support growing medium and vegetation, are a relatively new phenomenon. However, green roofs or sod roofs in Northern Scandinavia have been around for centuries.

A number of European Countries have very active associations promoting green roofs, including Germany, Switzerland, the Netherlands, Italy, Austria, Hungary, Sweden, the UK and Greece.

Many green roofs are installed to comply with local regulations and government fees, often regarding storm water runoff management.

In areas with combined sewer-storm water systems, heavy storms can overload the wastewater system and cause it to flood, dumping raw sewage into the local waterways. Green roofs decrease the total amount of runoff and slow the rate of runoff from the roof. It has been found that they can retain up to 75% of rainwater, gradually releasing it back into the atmosphere via condensation and transpiration, while retaining pollutants in their soil.

Canada

The city of Toronto approved a by-law in May 2009, mandating green roofs on residential and industrial buildings. There is criticism from that the new laws are not stringent enough, since they will only apply to residential building that are a minimum of six store’s high. By 31 January 2011, industrial buildings will be required to render 10% or 2,000m² of their roofs green

Costs

A properly designed and installed green roof system can cost 5 to 10 dollars per square foot. In Europe a well-designed and professionally installed fully integrated green roof can cost anywhere between 100 to 200 euros per square meter. The cost depends on what kind of roof it is, the structure of the building, and what plants can grow on the material that is on top of the roof. In the Spring 2007 issue of the Green Roof Infrastructure Monitor (Green Roofs for Healthy Cities web site), Jorge Braining reflects the wind and fire loads of green roofs and how German insurance companies handle extensive green roofs

DIS-ADVANTAGES:

The main disadvantage of green roofs is the higher initial cost. Some types of green roofs do have more demanding structural standards especially in seismic regions of the world. Some existing buildings cannot be retrofitted with certain kinds of green roof because of the weight load of the substrate and vegetation exceeds permitted static loading. Depending on what kind of green roof it is, the maintenance costs could be higher, but some types of green roof have little or no ongoing cost. Some kinds of green roofs also place higher demands on the waterproofing system of the structure both because water is retained on the roof and due to the possibility of roots penetrating the waterproof membrane.

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