Pros and Cons of a Green Roof: Computational Simulation of the Impact of Green Roofs in Urban Environment and Buildings on Brazilian Weather

Climate change presents itself as one of the main risks to urban environmental quality in this century. Therefore, mitigation and adaptation strategies to climate change must set a new agenda to public policies that conciliate development and natural preservation in cities across the globe. However, this comprehension requires actions in different scales and for diverse climate context. Facing these phenomena, the use of green roof (GR) is a fundamental strategy of mitigating and promote thermal comfort in cities. In this context, GR is vastly adopted as a solution for indoor and outdoor comfort. However, its impacts are hardly controversial. This paper presents the GR impact in the outdoor and indoor thermal comfort of a tropical weather context: Brasilia city. It is performed a study evaluating different GR parameters as soil thickness, plant height, leaf area density (LAD) with ENVI-met (v.4) software for urban thermal comfort and EnergyPlus software through the graphical user interface DesignBuilder (v.6) for the building thermal comfort. The complete neighborhood is analyzed for the urban scale, while for the building scale, only one typical building is assessed. The results show a maximum decrease of 2°C in outside temperature. However, closer to the lowest buildings, the benefits are more remarkable with a maximum reduction of 4°C. Higher LAD presents the most considerable improvement and is the only significant parameter according to statistical analysis. For the indoor thermal comfort, there is an overall improvement of 5% of the percentage of occupied hours in comfort (POC) according to adaptative comfort. However, on the upper floors, the advantage of the GR is more noticeable, with an average POC’s increase of 15%. The variation of soil thickness and LAD revel significant impact on the internal thermal comfort; Nevertheless, while soil thickness minimizes discomfort for cold, LAD reduces discomfort for overheating. In conclusion, the research shows that the impact of GR in thermal comfort is mainly localized, closer to the user, on the street and the upper floors. Also, the parametric study indicates that the GR parameter variation must be investigated to produce a more suitable solution to a specific condition, culture, and climate.