Greenhouse gas emissions and sustainability of green roofs and stormwater systems at a district level – comparisons with a life cycle perspective

¹ RISE -Research Institutes of Sweden, Department Built Environment, 50115 Borås, Sweden
² Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, 97187 Luleå, Sweden
³ RISE -Research Institutes of Sweden, Department Built Environment, 41258 Göteborg, Sweden
⁴ RISE-Reserach Institutes of Sweden, Department Built Environment, 11428 Stockholm Sweden

^* Corresponding author: jutta.schade@ri.se

Abstract

To reach future climate targets, it is important to verify that materials and technologies used for construction are sustainable and have a minimal environmental impact. The goal of this project was to add a broad life cycle perspective for quantifying energy and greenhouse gas emission, from the upstream flow of the construction process and the operational phase by including buildings and stormwater systems at a district level. The hypothesis was that green roofs might have a higher impact on greenhouse gas emissions as more material is needed compared to a standard roof. In return, green roofs reduce and retain stormwater, which may reduce the risk of hydraulic overloading in connected stormwater systems. This may lead to reduced CO₂ emission if an upgrade of existing systems is not necessary. To evaluate this complex issue, a framework was developed combining construction modelling, energy simulation, stormwater system modelling, and life cycle assessment. The result of this theoretical study indicates that green roofs reduce and retain stormwater but are in most cases not sufficient to reduce the risk of hydraulic overloading in connected stormwater systems. The results demonstrated that green roofs should be not solely implemented to reduce and retain stormwater in the Nordic climate.