• Longer lifespan of roof weather proofing thanks to protection from UV rays, extreme temperatures, hail and residue build-up
• Rainwater retention (approximately 30-99% of the annual precipitation, according to region and green roof type)
• Reduction of municipal wastewater costs (implemented in some communities, to be implemented in others)
• Minimization of runoff points
• Improved heat and cold insulation
• Ecological equaliser according to the interference-compensation scheme with the creation of living space for plants and animals
• Acknowledged "unsealing measures" of many communities in the wake of ecological rainwater management
• Improvement of the (local) environment through evaporation and transpiration facilitation
• Filtering of dust and other air pollutants
• Improvement of human living and working environments, especially through visible and physically-accessible green roofing
• Large-surface design elements for urban and landscape planners
• Wind protection to ensure security of roof weather proofing
• Improvement in sound insulation over the overall surface thanks to good acoustic absorption of the vegetation
• Reduction in electric smog

In Germany, two legal requirements are important to green roofing: the interference-compensation provisions of the Federal Nature Conservation Act (§ 19) and the development of divided municipal wastewater costs, which will be collected in all provinces through a split municipal wastewater fee. In practice, this means that many roofs must be “greened” due to construction and conservation obligations. Green roofing is also becoming more popular as it saves on rainwater storage costs.
 
At this time, green roofing construction does not meet the terms of thermal insulation regulation as currently defined. The reason given for this is that the structure is regularly soaked, which can lead to cold spots. However research by KOLB (1988), KÖHLER (2006) and MINKE (2009) has shown that green roofing has heat insulating properties which offer significant thermal insulation. In any case, there is still a need for research and action in this area, as well as in the fields of “sound insulation” and “dust filtering”.

Sustainability of Green Roofing

The sustainability of buildings is defined above all in economic, ecological and social terms. How does green roofing measure up?  

Economy
In this section, all of the economic effects of green roofing are considered, including both the direct and indirect financial savings it facilitates. These serve as the basis for various cost-benefit considerations. Previous cost-benefit analyses conducted by HÄMMERLE (1995 and 2002), KOLB (1997), MANSCHEK (1997), LIETCKE (1998), HOFFMANN (1999), KRUPKA (2001) and MANN (2003) are impossible to compare directly because of their different results. The first to complete a detailed analysis, HÄMMERLE led the way with his 1995 publication, which many authors later turned to as a guide. Ultimately the research of these authors agrees upon one point: green roofing pays off.

• Roof weather proofing is protected from extreme temperatures in summer and winter, and against wind, storms, hail, and ultraviolet radiation. This gives green roofing a longer lifespan than conventional roofing. Experts suggest that green roofing can go twice as long without repairs or total refurbishing than conventional roofing. Although concrete numeric data is not yet available, green roofing’s heat insulation properties in winter and heat shield abilities in summer undoubtedly contribute to energy conservation. Combining solar and green roofing also increases efficiency of photovoltaic systems.
• Rainwater retention: Depending on type of greenery, 30-99% of annual precipitation can be saved and runoff reduced up to 100%. This potentially saves on wastewater drainage costs, and on related costs like pipe and duct sizing. Economized rainwater storage may decrease costs in cities under the divided waste water statute.  

Ecology
Following are the points relating to ecological and environmental concerns.

• Ecological compensation is achieved through replacement habitats for animals. Approved mitigation measures are recognized by the intervention-compensation scheme. Depending on the type of greenery, it is possible to develop permanent habitats with high degrees of biodiversity in flora and fauna (MANN 1998).
• Selected green roof systems with ecological balance and a decentralized substrate may minimize transport distances.

 
Social
This area focuses on those points which can be seen as relating to “quality of life”, and which the greening of rooftops affects either directly or indirectly.
 

• Evaporation of stored water improves the surrounding climate through the resulting effects of cooling and increased humidity.
• Improvement of sound insulation due to the greater vibration frequency of the total surface. Good acoustic absorption resulting from properly-structured vegetation.
• Filtering of air pollutants and particle matter, and reduction of electric smog.
• Improvement of human living and working environments, especially through visible and physically-accessible green roofing, as well as residential living and otherwise usable areas.

 
There is a noticeable tendency to combine intensive greening with leisure activities and high-traffic areas. Department stores, shops, malls, hotels, schools, day-care centres, parking garages, and more are no longer created as simple “living spaces” for humans. They serve as sport fields and play areas, places to rest and retreat, and areas where old and young come together.
What is so appealing to investors is the fact that the land where these useful areas are built is free. It has already been paid for and can serve as the building base for a “secondary purpose”. What’s more, the costs of the intensive green roofing as described are far less than the costs of a new building. A simple glance at the price of land tracts in major towns is proof enough. There is also the fact that free building lots are difficult to find in major urban centres.