PURPOSE: To improve waterproof property of the bent part of a roof by providing a second waste plate part in draining material lower than the joint line of upper and lower sheathing roof boards between a roofing tile at the joint line and another roofing tile fixed on the upper face.

CONSTITUTION: Draining material 7 is extendingly provided along the joint line 6 of an upper sheathing roof board 1 and a lower sheathing roof board which are different in gradient. The first waste plate part 9 in the draining material 7 positioned upper than the joint line 6 is provided between the upper sheathing roof board 1 and roofing tiles 5, 5 arranged on the upper face. The second waste plate part 10 in the draining material 7 positioned lower than the joint line 6 is provided between the roofing tile 5 arranged at the joint line 6 on the upper face of the lower sheathing roof board 2 and the other roofing tile 13 fixed on the upper face of this roofing tile 5. Further, it is favorable to form a multiple folding back part 12 having a pair of bent parts 11, 11 in parallel, between the first waste plate part 9 and the second waste plate part 10 in the draining material 7.