Urbanisation has increased the worlds' cities populations and influenced the living conditions within these cities. Temperatures rise, the air becomes more polluted and noise levels increase. It has been proven that types of vegetation such as plants and trees can reduce the negative effects of urbanisation by for instance cooling cities, filtering the air or damping out noise. Due to the limited space in urban areas, placing vegetation on building façades and roofs can be a practical solution to gain the benefits of natural elements without the need for large pieces of land. A total of seven benefits provided by greenery systems can be distinguished which were researched intensively, however it is unknown how these benefits compare to the downsides of adding extra loads to a structure, which come in the form of extra material use and lead to an increased environmental impact for the building. In this research these benefits and downsides were compared to determine whether the application of greenery systems actually makes the building more sustainable or not. In this research the effect of six horizontal greenery systems (also known as green roofs) and eight vertical greenery systems (also known as green façades) on the sustainability of the building was assessed.
The effects of the benefits of the greenery systems on the sustainability of the building were determined using three different certification methods: BREEAM, LEED and WELL. In these certification methods credits related to one of the seven benefits can award the building a preset number of points, thereby increasing the overall amount of points awarded to the building. The impact of extra material use was determined using the environmental cost indicator (ECI), after determining the needed element sizes. The percentage increase of the sustainability certification score and the ECI were compared to determine which of the two has a higher percentage increase. When the increase in the sustainability certification score is larger than the increase in ECI, the greenery system receives a 'positive score' meaning the building has become more sustainable. If this is the other way around, the greenery system has a 'negative score' meaning application of the greenery system has made the building less sustainable. When both are equal the system has a 'neutral score'.
This research has shown that it is currently not possible to value all aspects of greenery systems in the certification methods used. Nonetheless, greenery systems lead to an increased sustainability of a building in 52% of the tested cases. The nature roof always receives a positive score and application of a direct green façade can result in a positive or neutral score but never a negative score. These two systems can thus always be applied to a building without having a negative effect on the building's sustainability. There is potential for modification of the existing certification methods so they can score all benefits provided by the greenery systems properly, giving more insight into the impact of these greenery systems on a building's sustainability and potentially affecting the number of cases with a positive score.