Green roof system is classified as intensive greening, extensive greening or mix of intensive-extensive greening. Recently, light-weigh green roof has been performed actively, because buildings have been considered loads, design and maintenance. This study was conducted to design soil depth for light-vegetation block with using bottom-ash. As a result, it was found that growth of plant had no direct effect on soil depth even it was less than 10cm. Soil depth having under 5cm could be integration of plant roots and vegetation blocks. It was also possible to grow organic vegetables through the experiment of planting. According to this experiment, as light-vegetation block with bottom-ash was used for planting, it makes design shallow soil depth. The results will help install green roof system conveniently not only new buildings but also used buildings.