Green Roof
From Swikipedia
Introduction
Green Roofs have become a very important component of sustainable urban development within the last 30 years. Growing environmental awareness and the striking economical and ecological advantages are the driving forces for this great success.
A green roof is a roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane. This does not refer to roofs which are merely colored green, as with green roof shingles. It may also include additional layers such as a root barrier and drainage and irrigation systems.
Brief Description
Benefits of Green Roofs:
Green roofs are used to:
• Grow fruits, vegetables, and flowers
• Reduce heating (by adding mass and thermal resistance value) and cooling (by evaporative cooling) loads on a building — 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
• Increase roof life span
• Reduce stormwater run off
• Filter pollutants and carbon dioxide out of the air
• The soil and plants on green roofs help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies.
• Filter pollutants and heavy metals out of rainwater
• Increase wildlife habitat in built-up areas
Disadvantages:
Green roofs have more demanding structural standards. Some existing buildings cannot be retrofitted with a green roof because of the weight load of the soil and vegetation. Depending on what kind of roof it is, the maintenance costs could be higher. 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. Installing adequate waterproofing systems and root barriers can increase the cost of the roof.
Types:
Two types of green roof exist: intensive and extensive. Intensive green roofs are essentially elevated parks. They can sustain shrubs, trees, walkways and benches with their complex structural support, irrigation, drainage and root protection layers. The foot or more of growing medium needed for an intensive green roof creates a load of 80-150 pounds (36-68 kilograms) per square foot. Extensive green roofs are relatively light at 15-50 pounds (7-23 kilograms) per square foot. They support hearty native ground cover that requires little maintenance. Extensive green roofs usually exist solely for their environmental benefits and don't function as accessible rooftop gardens.
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