PURPOSE: To improve heat insulating performance during the summer period and the dehumidifying performance during the winter period and to improve the efficiency of construction and the yield rate of a material by providing an air passage communicating in both directions of the long side and the short side of a sheathing roof board panel for heat insulation and ventilation between the sheathing roof board and a heat insulation layer.

CONSTITUTION: A sheathing roof board 1 is integrated with a heat insulation layer 2 through spacers 3 disposed like an island under the sheathing roof board 1. An air passage 4 is formed by the spacers 3, the sheathing roof board 1 and the heat insulation layer 2. Thus, the air is let flow in the directions of the long side and the short side as shown by an arrow 5. Thus, dew condensation is hard to occur, and the durability of a building can be improved remarkably.