Many people don’t know what green roof is. So, what it is? A green roof is not a surface painted green, it is a living surface of plants growing in a soil layer on top of the roof. A thinner or thicker soil layer is spread over the roof membrane itself, sometimes with a protective root barrier, often with a drainage layer underneath. On the substrate, draught-tolerant species of plants are grown. Roof vegetation like this one doesn’t at all damage the waterproofing membrane of the roof. In fact it protects it from the uv-light which does damage the membrane over time. There are two types of green roofs: extensive and intensive. There are some differences of its. An extensive roof has very thin soil layers, draught tolerant plants and requires little or almost no maintenance. The limitation here is in the choice of plants. Extensive roof can be established on a very thin layer of soil. An intensive roof garden has much thicker soil layers, and can look like an ordinary garden, with trees and shrubs. Intensive roofs are more park-like with easy access and may include anything from kitchen herbs to shrubs and small trees. This of course needs as much maintenance as a garden does, and can only be constructed on a roof that can bear heavy loads. (http://en.wikipedia.org/wiki/Green_roof)
It doesn’t matter what type roof is, but construction is a similar. Construction includes drainage materials, plant materials and establishment methods. For each green roof project, different site conditions and your aims and motives will govern the choice of materials and establishment methods. Therefore, if you are planning to build a green roof, consider the following two sections carefully. There are some roof sections which are important. First is a waterproofing. The membrane is made waterproof, and it will stay waterproof unless it gets physically damaged or aged. What ages a bitumen membrane is mainly uv-light and temperature extremes. Unless the roof membrane is damaged while laying the green roof, the soil and vegetation cover protects the membrane from these types of injuries later. (http://www.greenroof.se/?pid=32&sub=19)
Second section is root barrier. The asphalt waterproofing itself is not classified as root resistant and had to be reinforced with a root barrier. This barrier consists of rubberized asphalt enforced with polyester and treated eight a root-repelling agent. There are also synthetic waterproofing membranes (like PVC liners) available that are root resistant and do not require an additional root barrier. Different countries have different building practices and rules for green roofs - and many countries have no rules at all yet. In Germany, for example, a root barrier is always laid under a green roof. This is to ensure that no roots can damage the waterproofing. A root barrier is sometimes incorporated in the drainage layer. It can be chemical and poisonous to plants, or it can be a thin copper sheet, or rubber sealed so as to avoid seams. If your motive for having a green roof is sustainability and ecological consciousness, it’s a good idea to ask your contractor about the method. In Sweden, the usual practice is that under extensive roof vegetation (2 - 5 cm soil), where only sedums and moss can survive, an extra root barrier is not considered necessary, since the sedums used have weak roots, and moss has no roots at all. When the soil layer is thicker, and therefore can hold more water, other plants grow there, and there is a risk of getting weeds with more penetrative roots. Second layer is insulation. Insulation boards can be made from extruded polystyrene which has high water resistance and compressive strength. The main difference from the old roof is that the insulation layer must be places above the waterproofing membrane, but on the new roofs insulation must be located below the waterproofing. Second, but not less important, is drainage. The main reason for using a drainage layer is that if a lot of...
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