Abstract
This paper discusses slab surface temperature characteristics of a planted roof. Experiments are carried out for the planted roof of 100mm thickness soil layers installed in the Polytechnic University in Sagamihara through the summertime of 2002. Two kinds of soils and two kinds of plants are employed for the comparison. Besides, wooden decks are installed next to the planted roof and their thermal performances are compared to the planted roofs. One surface is painted in white and the other is not. Thermocouples are set at the center of each layer of the planted roof for the temperature measurement. The measurement is carried out by a data logger and the data are recorded every minute on a computer. Thermal evaluations are given for a sunny day, a cloudy day and a rainy day by analyzing the sampling data statistically. As a result, it is observed that under the planted roof the slab surface temperatures are maintained constantly. The wooden decks avoid the influence of solar heat and under that the slab surface temperature is kept nearly equal to the outside air temperature. The bare surface temperature of the roof concrete slab increases nearly 60℃ in a sunny day and changes between 20℃ and 60℃. At 100mm below the soil surface, the temperature fluctuations are mitigated by the thin soil layer. It is more effective to employ a wooden deck for the decrease of a slab surface temperature than to employ a planted roof according to the time-averaged data. The soils store solar heat gain and do not decrease the slab temperatures as the outside air temperature decreases. However, a planted roof is more favorable to maintain the slab surface temperature constant according to the standard deviation of the data. The thermal effect by a planted roof does not depend on whether the soil is planted or not. A planted roof should be treated as a method to carry out the green policy for metropolitan areas, but the thermal properties should be appreciated to achieve a sustainable building.
