Thermally insulated roofing device

One subject of the present invention is a roofing device ( 1) comprising an area support (2) made up of panels of wood particles on which a vapor barrier first layer (3)， an insulating second layer (4) and a third layer (5) that is impermeable to liquid water are laid.Said device ( 1) is one wherein the second layer (4) is a composite layer formed by the superposition of two distinct homogeneous elementary layers (6 and 6′)， namely a lower elementary layer (6) of wood fiber and an upper elementary layer (6′) made up of a material that is at least partially bio-sourced， that has hygroscopic， antifungal and thermal-insulation properties and that has a low resistance to the diffusion of water vapor.