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Green Roof Systems - What Exactly Are They?Green roof systems...we are hearing about them more and more. Whether it be for commercial uses or even residential design, green roof technology is speeding ahead. Green roofs can be installed on both flat and pitched roofs, although there is a maximum recommended slope for roofs that are pitched. Irrigation is not typically needed if the green roof construction is done correctly. However, if required, drip or spray systems should not be used. The plants should be watered at the roots, where it will not evaporate. There are a variety of plants that can be used. Sedums are extremely common due to their shallow root system. In addition, meadow grasses and perennials can be used. Trees, too, can be part of a green roof system. The types of plants utilized will depend on the type of green roof being installed. Full coverage will take about two years. Green roofs are also called eco-roofs or living roofs. If you were to look at a cross section of a green roof system, you would typically see the following layers:
However, not all green roof installations are done in the same way or contain the same layers. It can depend on many things. There are lightweight systems for shallow plants and there are also heavier systems for plants with deeper roots....even trees. A green roof can do many positive things for our environment. Green Roofs and Storm Water Management Benefits Green roofs control stormwater runoff by allowing the water to seep into the plant roots and soil. With the standard roof, water from the roof must be channeled to an acceptable area. If not done correctly erosion can occur, along with pollution. A typical green roof system can retain up to 50 percent of a one-inch rainfall, thus greatly reducing the water runoff. Any water which is released is done so at a slower rate having a much less severe impact on the environment. Roof Life is Extended Tremendously Studies in Germany have shown green roofs can extend the life of the roof by at least two time and sometimes longer. It protects it from wind-blown debris and shields it from UV radiation. By buffering temperature extremes (see below), the stress of expansion and contraction is minimized. Urban Heat Island Effects are Greatly Improved Most roofs are made of a dark color and can reach temperatures of 150 to 190 degrees. In urban areas, temperatures can be 2 to 10 degrees hotter than those in rural areas. So how do green roofs help this situation?There are a few different ways: Evapotranspiration (not that complicated...read on!) Moisture is retained in the roots of the plants. The plants then absorb this water, which then evaporates through the leaves. This cools the air above th roof surface. Thermal Mass Effect Large amounts of heat can be absorbed and stored by a green roof. While normally, heat from the roof is transposed to the building interior, with green roofs, the heat can be absorbed and stored there. The heat is released once the air cools down. This eliminates building temperature extremes, reducing cooling demands. Shading Plant foliage can actually provide shade, which also helps to cool the roof. Additional Advantages of Green Roofs
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