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Home / Garden Roof / Green Roof Benefits/Facts

While there are similarities among green roofs, each installation is unique, and benefits will vary by region, climate, building, and green roof type and design. National Roofing Company’s team of professional estimators and certified garden roof installers can offer expert advice when deciding whether to incorporate a Garden Roof in your new construction or re-roof build. The following benefits however can be achieved with virtually all green roof infrastructure systems

A green roof system protects the waterproofing membrane from climatic extremes, UV light & mechanical damage and in so doing almost doubles its life expectancy. Therefore, by installing a good quality waterproofing system, a normal 30 year life expectancy can to last up to 60 years, thus saving the client the cost of re-waterproofing during the average building’s expected lifetime.

Green roofs have a positive effect in terms of thermal insulation through their ability to cool buildings and insulate them during the winter [dependent on daily conductance of the green roof]. A London study revealed that the application of a retrofitted green roof on a building had reduced the need for cooling/heating of theindustrial plant in the floor beneath. Since the green roof has been installed, cooling and heating fans have not been used, resulting in an estimated savings of 25.9 MW per year, which at current rates is approximately a £4,300 ($6,700 USD) saving per year. If the green roof had been installed as part of the original design of the building and the ability of the green roof to reduce cooling and heating requirements had been known, there would have been a potential saving of £10,000 ($15,500 USD) due to reduction in the need to replace heating and cooling equipment in the floor in question.

Research from the Tyndall Centre for Climate Change suggests we need a 10% increase in green space in our cities to combat climate change. This is particularly relevant to the reduction in the Urban Heat Island [UHIE]. Green roofs are recognized to have a positive effect on reducing the UHIE. A modeling scenario undertaken in New York by the New York Heat Island Initiative determined that providing 50% green roof cover within the metropolitan area would lead to an average 0.1- 0.80C reduction in surface temperatures. For every degree reduction in the UHIE roughly 495million KWh of energy could be saved.

Green roofs can provide important refuges for wildlife in urban areas. Research in Switzerland and the UK has demonstrated that green roofs can provide important refuges for rare invertebrate populations. While garden like in character, semi-intensive and intensive garden roofs provide a significant resource for local biodiversity with good planting schemes, which include native and flowering plants that attract butterflies and bees. Additionally, inclusion of water features, dead logs and nest boxes can increase the potential for such roofs to act as a resource for local wildlife and migrating birds.

Green roofs can significantly reduce the surface run off volumes and rates of rainfall leaving roofs. As a source control mechanism in the sustainable urban drainage system, green roofs can help reduce flash floods as a consequence of intense rainfall events. This will become increasingly important as a consequence of climate change. Green roofs also improve the quality of water, and although the amount of water is reduced, it is possible to harvest rainfall from roofs that have been greened.

Green roofs cannot be given a U-value at present. However they have been shown to significantly reduce the need for air conditioning in summer and can provide a degree of insulation in winter. The use of a green roof compared to conventional roofing surfaces can have a significant impact on the energy balance within a given building and on the immediate environment. This is particularly relevant if a building has poor insulation and poor ventilation, which can lead to increased use of air conditioning and therefore increased energy use. Studies have shown that the membrane temperature beneath a green roof can be significantly lower than where the membrane is exposed.

The combination of soil, plants and trapped layers of air within green roof systems can act as a sound insulation barrier. Sound waves are absorbed, reflected or deflected. The growing medium tends to block lower sound frequencies while the plants block higher frequencies. The amount of sound insulation is dependent on the system used and the substrate depth. A green roof with a 12 cm substrate layer can reduce sound by 40dB and one of 20 cm by 46-50dB; yet even limited coverage can help with sound insulation. This could be particularly important in areas of high noise pollution ,such as airport landing zones, to airports, as these levels are sufficient to provide noise insulation to buildings under aircraft flight paths.

The original green roofs in Germany stem from covering wet bitumen with 6cm of sand, which became vegetated. This covering was to protect the wet bitumen from fire. Green roofs have now been shown to double if not triple the life of waterproofing membranes beneath the green roof.

In dense urban environments there is often a lack of green space for residents. Roof Gardens and roof top parks provide important green spaces to improve the quality of life for urban residents. The Urban Green Spaces Taskforce (Green Spaces, Better Places, 2002) demonstrated the various benefits that green spaces provide, such as ecological function, visually softening the built environment, supporting biodiversity, aiding peoples' mental and physical health, and providing a communal focus and sense of place.