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A short guide to green roofs

The benefits of green roofs

There is much today that is in favour of a green roof. The benefits of a properly constructed green roof are obvious.
A green roof is not only attractive, but also provides environmental, social and financial advantages.

The benefits of a green roof in overview:
(No claim is made that the following is exhaustive!)

 Benefits of green roofs       Comments
  • Compensation for the loss of
    green space
  With the increasing construction of buildings in urban and now even rural areas, we are gradually losing the free green space required to maintain the environment. The construction of green roofs or planting on built-up areas means that the loss of green space can be - at least partially- compensated for and the impact on nature reduced to a minimum.

  • Retention of water and 
    rain water run-off attenuation
  There is no doubt of the ability of the roof fabric and the vegetation of a green roof to store and retain rain water. This temporary storage and attenuation of run-off helps prevent local drainage systems from overflowing during times of persistent or heavy rainfall.

  • Reduced roof surface 
    temperature on exposure to the sun
  The layer of vegetation on a green roof prevents overheating of the roof and thermal reflection. As the surface temperature of a green roof is cooled, this also inhibits overheating of the rooms immediately below and the immediate surroundings are no longer exposed to reflected heat.

  • Evaporation of stored water
  The moisture stored in the fabric and vegetation of a green roof is returned to the environment by natural evaporation. This also has a positive effect on humidity. The cooling effect associated with evaporation reduces the surrounding temperature and provides a beneficial microclimate. The quantity of water run-off into the local drains system is also reduced due to this water evaporation, cutting down on system overload.

  • Protection of the roof fabric
  One important function of a green roof is to provide effective protection of the roof structure. The green roof preserves the bearing, insulating and impervious characteristics of the roof itself against the influences of the environment and the weather, and also against mechanical effects, thus extending roof life.

  • Reduction of temperature variation
    of the roof fabric and thus reduced
    roof fabric temperature
  Extreme temperatures can sometimes develop on a "standard" roof during the various seasons. These can range from near -20°C to as much as +80°C. A green roof - depending on build-up height - protects the whole roof fabric from the effects of these extreme temperatures and temperature variations. This slows down material ageing and wear.

  • Improved insulation due
    to higher temperatures
    on the roof surface
  A green roof not only prevents overheating of rooms immediately below the roof at times of powerful solar thermal radiation, but also provides added insulation during winter. Thanks to the insulating effect of a green roof, loss of heat from the roof is reduced, and the rooms below stay warmer.

  • Protection against ultraviolet radiation
  Depending on build-up height, a green roof can also protect the roof fabric against the effects of ultraviolet and ultrared radiation. This also slows down material ageing and wear in the roof structure.

  • Increased noise insulation
  A green roof, depending on build-up height, also reduces noise emission and immission. This effect of a green roof thus can bring about a considerable improvement to noise pollution in buildings and their surroundings. This aspect is important in both the private and commercial spheres.

  • Extends roof life
  A green roof provides the roof fabric with protection against all external influences. This is particularly important with respect to the damage to the impervious qualities of a roof that can be caused by the environment, the weather and mechanical effects. Assuming that initial roof integrity is provided, a green roof will provide the best possible protection against ageing and mechanical damage.

  • The vegetation absorbs  
    dust and airborne contaminants
  The leaves of the vegetation on a green roof have a particularly high urface area and thus have an excellent filtering effect with regard to dust and airborne pollutants. Particularly when moist, roof vegetation can absorb up to 20% of the dust and pollution in the air. This results in an apparent increase in the oxygen content of local air, which promotes a sensation of well-being.

  • Substitute habitat for plants and animals
  Green roofs can provide a habitat for plants and animals even in built-up urban areas. The extreme situation on the roof means that flora and fauna can find a home in places in which their natural habitat has already been lost - e.g. plants unable to grow underfoot and ground-nesting birds. A green roof can thus provide a "foothold" biotope.

  • Cost reductions

Many local authorities and communities encourage the construction of green roofs by, for example, providing financial incentives. However, there are differences between the various regions, so that there is currently no standard policy in this respect. The various local bodies (planning authority, parks authority, environmental agency) should be able to provide the required information. In addition to financial subsidies, a reduction in water rates may also be possible in some regions. Other cost-saving effects of a green roof are the reduction in the expense of heating and air-conditioning, in building maintenance and the fact that an extra dedicated green space and the additional expensive of its upkeep are no longer required.

  • Improvement of the working
    and living environment

Green roofs in residential and commercial locations offer several advantages all at once. The advantages associated with building regulations should not be ignored. In industrial zones, green roofs provide a substitute for the area lost to building. A green roof can count towards the green spaces required by the local building regulations, and can also provide a utilisable green area. On various floor levels of the building, the land used for construction can be reused, as it were, without having to extend the building - as garden terraces, for example, to provide an inviting rest area for employees. Green roofs provide a pleasant contrast to the general drabness of an industrial landscape. Green roofs in residential areas are also attractive and utilisable free spaces, which do not require their owner to purchase additional building land. These spaces can be multifunctional, and if used as a roof or terrace garden, offer many recreational possibilities.

Most green roofs are not only suntraps, but, depending on the vegetation used, can also provide seclusion from the enquiring gaze of the neighbourhood, so that a family can relax in private on its own rooftop, frequently with a magnificent view over the surroundings.

  • Improvement to the appearance
    of the urban landscape

In recent decades, the building developments in high-density municipal and even rural areas have made a lasting impression on the landscape. Although these developments were essential, they are frequently anything but attractive and in many cases can been viewed as a form of visual environmental pollution. One way to counteract this is to develop green spaces and recreational areas. The modern green roof systems can provide a contribution towards this. Green spaces can thus be created in areas where it would otherwise be impossible to plant vegetation. In the densely built-up urban areas, where every square metre is covered in concrete or asphalt, construction of green roofs considerably increases the proportion of green space. Buildings are made more attractive, and can be even better integrated in the rural environment.

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