Extended Roof Life
A green roof system will protect the waterproofing membrane from the vagaries of the weather, damaging ultra violet light and mechanical damage. The life expectancy of the roof is almost doubled! Therefore you can expect a good quality root resisting waterproofing system to last up to 60 years rather than the usual 30 years. This cost benefit alone far outweighs the cost of installing and maintaining a green roof system.
Green roofs offer significant thermal insulation benefits through their ability to cool buildings in the summer and insulate them during the winter.Studies have shown that green roofs can contribute to savings in heating costs. An industrial plant in Frankfurt , which had a green roof installed, recovered the cost of the green roof in 2-3 years through the savings in both heating and cooling costs including the costs associated with maintaining / replacing the required heating and cooling equipment.A conversation with a building services manager in London happened to uncover that the application of a retrofitted green roof on a building had reduced the need for cooling / heating of industrial plant in the floor beneath. Since the green roof has been installed cooling and heating fans have not been used. It was estimated that about 25.9 MW per year was being saved. Based on electricity rates current at that time, the saving amounted to approximately £4,300 per annum.
Surface water drainage capacity can be significantly reduced
Green roof installation could reduce the number of drainage outlets – a potential saving for developers. It has been pointed out that these benefits are unlikely to factor in as roof a drainage costs are traditionally costed separately.
However, depending on the size of the roof and the height of the building, the potential to reduce the number of drainage outlets at both roof level and ground level could significantly off set the cost of a green roof.
Reduce the noise level by up to 50 dB. 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 in a green roof will help to block lower sound frequencies whilst 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.
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Reduce the likelihood of local flooding
Green roofs store rainwater in the plants and growing mediums and evaporate water into the atmosphere. The amount of water that is stored on a green roof and subsequently evaporates is dependent on the growing medium, its depth and the type of plants used. In summer green roofs can retain 70 – 80% of rainfall and in winter they retain between 25 – 40%. Green roofs, therefore, reduce the impact of run off on the storm water drainage system, and reduce the likelihood of local flooding.