Paper Title
THERMAL PERFORMANCE OF ULTRA-THIN WETLAND GREEN ROOF IN SUBTROPICAL WINTER CLIMATE

Abstract
Under extreme climate, increasing maintenance in volume and frequency of irrigation under severe drought and increasing odds of drowned plants during intensified rainstorms lead to unstable plant growth in the terrestrial extensive green roof system which in turn jeopardized its thermal performance. An innovative kind of extensive green roof system with high resiliency toward extreme climate is in need. The research purpose is to investigate and compare the thermal performance of the ultra-thin wetland green roof and the traditional extensive terrestrial green roof during daytime and nighttime in humid subtropical climate. Wetland plants, that naturally grow in swamps or river bands can withstand constant fluctuation in water level, are excellent resilient plant materials in combating extreme climate. The effect of type and depth of growth substrate and type of wetland plants on thermal performance of the extensive wetland green roof are investigated, and then compared with the conventional extensive terrestrial green roofs and normal extensive wetland green roofs. The research adopts one three-stage field experiment conducted on the flat rooftop of one concrete building in Taichung, Taiwan. Results from the first stage demonstrated that the extensive field soil wetland roof without plant slightly outperformed the extensive coconut fiber and rock wool wetland roofs without plant in terms of the thermal performance during both daytime and nighttime. Results from the second stage showed that not only the extensive 10cm field soil wetland roof without plant has very similar thermal performance to that of a 20cm field soil wetland roof without plant, but also the extensive 10cm field soil wetland roof can significantly reduce the weight load of a building than the extensive 20cm field soil wetland roof. Results from the third stage demonstrated that ultra-thin 10cm field soil wetland roof with roundleaf rotala is beneficial for reducing the average temperature of bare rooftop by 8.790C, from 32.87 to 24.080C, during daytime, and increasing the average temperature of bare rooftop by 2.480C, from 22.03 to 24.510C, during nighttime. Using growth medium of same depth, thermal performance of roundleaf rotala outperformed water celery, tall scouring rush and waterhyssop due to its relatively weaker passive cooling effects by 0.32-1.910C during daytime, and relatively stronger thermal insulation effects by 0.70-2.260C during nighttime. Moreover, the thermal performance of the ultra-thin 10cm field soil wetland roof with roundleaf rotala was very similar to that of conventional terrestrial green roof containing 20cm lightweight soil and roundleaf rotala, and normal extensive wetland green roofs with 20cm wetland growth medium and roundleaf rotala. In sum, the thermal performance of the innovative ultra-thin wetland green roof with roundleaf rotala outperforms the conventional terrestrial green roof with only 50% depth of growth medium which, in turn, significantly lessen the weight load of the building. Keywords - Ultra-thin Wetland Green Roofs, Resilient Green Roof, Extreme Climate Adaption, Thermal Performance, Wetland Plant