Study on rooftop outdoor thermal environment and slab insulation performance of grass planted roof

The benefits of rooftop greening are ascertained in thermal perspective. It effectively reduces the near surface ambient temperature and the reflected irradiation from the rooftop slab, thus increasing the thermal comfort environment above the lawn and reduces the heat transferred through the rooftop slab. The former effect enables the potential usage of the rooftop spaces for human activity and helps to alleviate the urban heat island effect while the latter is able to reduce the interior space cooling load especially in subtropical climate. A field experiment was carried out in the subtropical central Taiwan to quantify these two performances. Indices of Mean Radiant Temperature (MRT), Wet Bulb Globe Temperature (WBGT), and heat flux rate were used to explain and discuss the performance of thermal comfort and heat flux of the rooftop lawn. The results confirmed that rooftop lawn contributes benefits both on its outdoor surrounding environment and the indoor energy beneath.