In a green roof system, the roof is covered with a waterproofing membrane, above which plants are grown. The waterproof membrane protects the building from water seepage, which can cause damage to the structure. Apart from the waterproofing membrane, this system requires additional layers, for drainage and irrigation. A layer that acts as a root barrier, is also required. This system helps to absorb rainwater, lowers the temperature in cities, provides insulation, and also offers a habitat for birds. A green roof, is also known as living roof, eco-roof, vegetated roof, or oikosteges.
Types of Green Roof
Green roofing system is classified into two types - intensive and extensive. This categorization is based on the amount of irrigation required, depth of planting medium, and the amount of maintenance required. Intensive ones require a good depth of soil to accommodate the growth of large plants and lawn grass. Such green roofs need more labor, power, irrigation, maintenance, and plant food. They can house any plant, from small trees to shrubs; and are easily accessible, like a park. Extensive ones are not meant for access, except for maintenance. Such a roof requires very less maintenance, usually once a year, for weeding or for fertilization. Normally, a thin layer of soil is sufficient for an extensive green roof top. A green roof system can also be differentiated as pitched and flat. Flat ones require more care with regard to waterproofing and drainage, as compared to pitched ones, which have slanting roof surfaces.
Tips for Building a Green Roof
- The first and foremost task is to obtain the permit to build a green roof in your building, from the concerned authority. Normally, this is issued by the Department of Construction and Permits. The laws may vary from one place to another. In some regions, incentives are offered for building a green roof.
- Do some research regarding the designs, and select one which is suitable for your building. You can even take the help of professionals for this purpose. Choose the type of green roofing (extensive or intensive) and the type of vegetation. It is very important to check whether your building is capable of bearing the load of the additional fixtures. It is observed that some old constructions are not well-equipped to accommodate a green roofing.
- If you are through with the first two steps, the next one is waterproofing the roof. Use a waterproof membrane to protect your building. There is a wide range of materials available for this purpose. You can use asphalt sheeting or specialized rubber sheets which are made for this purpose. Always make sure that the edges are covered.
- After waterproofing, install the root barrier. You can go for concrete or cellular glass, which is good for insulation.
- Next is the drainage layer. It helps in carrying the excess water to gutters, and prevents water retention on the roof. Normally, the drainage layer consists of gravel and pumice.
- Buy some good filter fabric, which allows the flow of water to the drainage layer, but prevent the movement of soil or growing medium to the lower layer. Usually, polyester or polypropylene is used for this purpose.
- The next layer is the growing medium. You can use cleaned top soil mixed with sand, or crushed clay and humus. Local soil is also good, but it has a possibility of growing weeds and pathogens. The ideal soil depth is said to be three inches.
- Drip irrigation is considered the best, at least for the first year of installation. This irrigation system is advantageous in saving water and your time, and is also useful in adding fertilizer.
- Select those plants, which are suitable for the local climate and environment. Give preference to those plants which are tolerant of sun, wind, frost, and drought.