Green RoofWhy have a green roof?

Installing a green roof goes a small way to replacing the nature destroyed by building. However, there are plenty of good reasons to incorporate a green roof into the design of a building or to install one on an existing building.

– Reduced energy consumption

Climate change means that it is essential that we vastly reduce the impact of building in terms of energy consumption and therefore carbon emissions into the environment. Since green roofs have significant insulation properties, providing warmth in the winter and cooling in the summer, they can have a huge effect on the way a building performs and should be incorporated into any package aiming to achieve zero or low carbon targets.

– Extended life of the waterproofing

The waterproofing under a green roof system is protected from the effects of ultraviolet light, extremes of temperature and weather. As a result the life of waterproofing is prolonged. Some planted roofs in the USA and Europe have extended the life of the waterproofing to 70 years or more!

– Noise reduction

Adding mass to the roof structure by planting enhances acoustic performance of the roof. Acoustic performance will vary with the water content of the plant system but sound transmission through an aluminium standing seam roof for example can be reduced by up to 40 percent. This benefit increases as the plants grow and mass increases.

– Stormwater management

In many cities around the world it has been recognized that the most significant ecological advantage of roof planting is in stormwater management. Development results in permeable ground being replaced by impermeable artificial surfaces through which rainwater can not permeate. The result is that drainage systems in developed areas are unable to cope with the instant changes in flow rate and volume of stormwater resulting in flooding and water course contamination.

Since it is difficult to install water containment measures within urban areas where space is at such a premium and ground based storage is expensive, keeping the water on the roof and returning it to the atmosphere is a cost effective solution. Rainwater retained on green roofs in the substrate and drainage layers is taken up by the plants and transported from the root to the leaf where it is lost through the leaf surface- a process known as transpiration. Water is evaporated from the substrate and plants by the sun. Both processes are accelerated by wind disruption. Any water that is not retained on the roof is released much more slowly into the drainage system preventing flooding.

– Maintenance

Intensive green roofs require regular maintenance. Simple intensive green roofs, like lawns, might require mowing and weeding on a weekly or fortnightly basis during the growing season. Extensive green roofs would normally only require annual visits to remove rubbish, check fire breaks and drains and in some cases remove unwanted colonising plants. The first three years of roof maintenance are usually the responsibility of the green roof manufacturer. Some ‘wildflower meadows’ on extensive green roofs may require annual mowing with cuttings removed.

– Benefits of Green Roofs

Even today the opportunities of Green Roofs are still underestimated. The “natural look” is only one obvious credit within the broad range of arguments for Green Roofs. Further benefits of Green Roofs include the protection of waterproofing, water retention, thermal insulation, improvement of the climatic environment as well as new natural habitats for flora and fauna. No other architectural style provides such a wide range of positive effects for buildings, inhabitants, and the environment. Thus, Green Roofs meet one of the essential conditions of sustainable development, the reconciliation between economy and ecology. It is very difficult to find positive arguments for bare or gravel led roofs. Lower building costs for “Non-Green Roofs” in comparison to a Green Roof, are weak arguments considering it is only a short term calculation. Long term costs of maintenance and repairs of ‘naked roofs’ are much higher than that of Green Roofs. It has to be considered that roofs belong to the most strained parts of a building; if no precautions are taken and product qualities lack, problems arise quickly.