Greenhouse gas emission and sustainability of green roofs and storm water system on a district level : Comparisons with a lifecycle perspective

To reach the climate targets in the future, it is important to verify that materials and technologies used for constructions are sustainable and have a minimal environmental impact. The goal of the project was to add a broad life cycle perspective for quantify energy and greenhouse gas emission, from upstream flow of the construction process and the operational phase by including buildings and storm water system on a district level. The hypothesis was that green roof might have a higher impact on the greenhouse gas emission as more material is needed compare to a standard roof. But in return green roofs reduce and retain stormwater which may reduce the risk for hydraulic overloading in connected stormwater systems. This may lead to reduced greenhouse gas emission if an upgrade of existing systems is not necessary. To evaluate this complex issue a framework was developed combining construction modelling, energy simulation, water system modelling and life cycle assessment. The result of this theoretical study indicates that green roofs reduce and retain stormwater, but in most cases not sufficient to reduce the risk for hydraulic overloading in connected stormwater systems. Furthermore, the energy benefits of the green roof compare to conventional roof on a high isolated roof in the Nordic climate are negligible. The results demonstrated that green roofs should be not solely implemented for reduce and retain of stormwater and for energy reduction in the Nordic climate. Moreover, green roofs should be implemented by considering other sustainable benefit, such as urban air quality, water run off quality, reducing urban heat island effects and preventing noise pollution