Today, a roof can do more than just protect your home and family against the elements. A green roof can go so much further, such as help insulate, save energy, and prevent urban heat islands.
A green roof, sometimes called a garden roof, or eco roof, is a roofing system designed to grow maintenance free plants on top of a specially prepared roof. You may be seeing more of them lately since the technologies have been improved, making installations more common on residential structures.
A green roof can absorb over 25 percent of the rain that falls on it, thereby reducing oily runoff that can pollute nearby lakes, rivers and streams. In addition, they are estimated to last about twice as long as a conventional roof. These eco friendly roofs can also prevent storm drains from overflowing, help to purify the air, and keep a rooftop up to 20 degrees cooler in the summer and warmer in the winter. That means less energy usage, lowered energy bills, and less pollution.
Green roofs are not necessarily new. Early settlers of the Great Plains lived in sod houses, as did Germans and Icelanders of centuries past. They carved these sod covered homes into the hillsides and then found that the vegetation growing naturally on their rooftops provided much needed insulation.
As beneficial as green roofs are, there are some things that must be taken into consideration. First, green roofs are not meant to be installed by nonprofessionals. The next consideration may be their weight. When saturated, the weight of each tray in the modules used for green roofing systems can add up to 30 pounds per square foot. A traditional roof is usually built to support about 25 pounds per square foot. You may want to consult a structural engineer to tell you if your existing roof is able to support the weight of a green roof or if your roof needs to be reinforced. They can also help you choose which type of green roof system best suits your needs.
Over time, green roofs gained more popularity being installed on flat surfaces in cityscapes. More recently, however, they have seen more use on private homes. The newest mesh screen technology keeps the growing medium and plants in place on a sloped roof. Although these systems vary, they commonly consist of several layers, beginning with plywood, concrete, or steel as the bottom layer. Next will come foam insulation, then, a waterproof barrier, followed by a polypropylene root barrier, some type of drainage layer, and then the mesh fabric that will keep the plants and growing medium in place.
The trays of plants are usually about one foot by two feet, weighing about forty pounds each. These trays are generally moved by forklift to the rooftop. The trays contain interlocking edges, and are then placed in rows and snapped together. The plants used for these systems are usually lighter, low maintenance varieties, often hardy, perennials that can tolerate drought well, such as sedums and other succulents.
There are also more elaborate green roofs which are generally heavier and deeper, often more of a roof garden, even growing small trees and shrubs. These tend to need more roof maintenance, such as fertilizing, watering, or even mowing.
Some European countries now mandate that new buildings use green roofs. During the 1990’s the mayor of Chicago began looking for ways to reduce the city’s urban heat-island effect, which occurs when dark surfaces such as rooftops absorb heat, raising local air temperature and increasing smog. Eventually, a 21,000-square-foot green roof was added to the top of Chicago City Hall. The mayors of numerous other large cities have since followed suit, as have many of our largest corporations. While the U.S. has a ways to go to catch up with Europe, the trend continues to grow in these energy and environmentally conscious times.
Guest Blog Written By: Alan Monzon
Arizona Roof Rescue
6069 N. 57th Drive
Glendale, Arizona 85301
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