PURPOSE: To conduct ventilation smoothly by installing a permeable board body capable of performing ventilation from a lower section to an upper section onto the external.surface of a roof beam, abutting the upper end section of a facing material against the external surface of the board body and communicating a permeable layer on the inside of the facing material with a section between a roof and a ceiling through the board body.

CONSTITUTION: A permeable board body 2 is mounted on the external surface of a roof beam 1 by bonding. The upper end section of a wall 3, in which a heat-insulating material 33 made of glass wool is set up between an interior finish material 31 and a facing material 32 and a permeable layer 34 is fitted between the heat-insulating material 33 and the facing material 32, is abutted against the external surface of the permeable board body 2. The upper end,$ surface of the wall 3 is stuck on the surface of the board body 2. Accordingly, air is flowed through a section 41 between a roof and a ceiling through the ventilation holes of the permeable board body 2 from the permeable layer 34 of the wall 3, thus air is ventilated.