General info of Green Roofs

Why install a green roof?

Installing a green roof has multiple advanteges, such as advantages for the community (e.g. water management, air & water purification, habitat development etc.) but, naturally, also advantages for the roof owner (e.g. loger lifespan of roofing, thermal insulation of the roof, sound isolation, visual benefits & financial benefits)

Source: brochure from Agentschap Natuur en Bos (Nature and Forest Agency, www.natuurenbos.be)

A. Advantages for the community

• Water management
  Because more and more surfaces are being paved, precipitation can often barely penetrate into the soil, and even relatively minor showers overload local sewer systems, resulting in local flooding. The solution: to immediately drain all precipitation (= enhance the retention of rainwater) for instance by constructing rainwater reservoirs or green roofs. Green roofs reduce the drainage of precipitation, meaning that peak flows are lower, the sewer system is not (or less) overloaded, and no (or less) serious flooding occurs.
• Air and water purification
  Green roofs not only absorb harmful substances such as CO₂, benzene, and dust particles, they also break them down. As such, green roofs contribute to a better environment through air purification. Also, green roofs provide water purification, as polluted precipitation first flows through a green roof filtering out part of the pollution before flowing into the waterways.
• Habitat development
  Green roofs may serve as a temporary habitat (as a stepping stone and as a temporary place of refuge), but also a replacement habitat and as a basic habitat. Blooming sedum plants are a major draw for butterflies and other insects that feed on nectar. Green roofs can therefore also make a contribution to the enhancement of biodiversity.

B. Benefits for the roof owner

• Longer lifespan for roofing
  A green roof lasts longer than regular roofing (even twice as long compared to a flat roof with bitumen covering). The presence of the layered construction protects the roofing from: UV radiation, heat, frost, and temperature fluctuations affecting the roofing surface, uneven heating of the different roof layers and against mechanical damage.
• Thermal insulation of the roof
  Green roofs mitigate temperature fluctuations, so the roof waterproofing is not only subject to a more moderate temperature regime, this also reduced heating costs in winter and cooling requirements in summer.
• Sound insulation
  The green roof absorbs sound.
• Visual benefits
  A view of greenery has a positive effect on a person’s mood, and therefore on a person’s physical health. Furthermore, the look of a green roof changes with the seasons, resulting in a pleasant variation of the view.
• Environmentally friendly image
  By creating a green roof, businesses will develop a more environmentally friendly image. Working in a green environment also has a positive psychological effect and may contribute to increased job satisfaction and thus a higher productivity.
• Financial benefits
  Most people assume that a green roof is more expensive than a traditional roof. This is true only if one compares the cost of purchasing a green roof to that of purchasing a traditional roof, but the longer lifespan enjoyed by green roofs ensures that the price difference in the long term is minute or non-existent.