Is it necessary to set a blind ditch when the planting roof is equipped with a drainage board?

The traditional drainage method is to use masonry tiles as the filter layer, and use more pebbles or gravel as the filter layer to discharge the water to the designated place. The use of pebbles, gravel, ceramsite and other filtering materials makes the structural layer thicker and the load is larger. Rainstorm drainage in rainy season is slow, especially after a long time, the roots of plants fill the cracks in the stones, which can't be drained at all, and at the same time, it also encourages the overgrowth of arbor plants, thus greatly increasing the load of the structural layer and reducing the original safety number of the floor, which has quite high security risks. At present, it is time-saving, labor-saving, energy-saving, investment-saving and building load-reducing to use the drainage plate instead of the cobblestone filter layer for drainage.