A roof window for installation in a roof structure of a building, wherein the roof window comprises a sash and a fixation frame, wherein the sash is connected to the fixation frame by means of a first hinge arrangement allowing the sash to be moved relative to the fixation frame between a closed sash position and an open sash position, wherein the sash comprises side members (8a, 8b), a top member and a bottom member which together encircles a sash opening, and wherein an insulated glass unit is installed in and connected to the sash, wherein the insulated glass unit comprises multiple glass sheets and a sealed inert gas or vacuum in an insulating space between the glass sheets, wherein the insulated glass unit comprises an inwardly facing major surface for facing the interior of the building and an outwardly facing major surface for facing away from interior of the building, wherein an outer weather shield is connected to the sash, wherein the outer weather shield is transparent to at least visible light and comprises an interior major surface and an exterior major surface, wherein the outer weather shield is configured to cover the sash opening and wherein an air gap is provided between the interior major surface of the weather shield and the outwardly facing major surface of the insulated glass unit, wherein the outer weather shield is connected to the sash so as to move together with the sash and the insulated glass unit when the sash is moved between the closed sash position and the open sash position, wherein the weather shield is further movably connected to the sash by means of a further hinge arrangement allowing the weather shield to be moved relative to the sash and the insulated glass unit between a closed weather shield position and an open weather shield position, wherein the exterior of the fixation frame defines an exterior frame plane defined by the outermost surfaces of the fixation frame, and wherein the exterior frame plane extends across and over the frame opening which is encircled by frame members (3a-3c) of the frame, characterized in that at least a part of the insulated glass unit is configured to move from a position above the exterior frame plane and into the frame opening when the sash is moved from the open to the closed sash position, so that the outwardly facing major surface of the insulated glass unit is placed in the frame opening below the exterior frame plane with a distance to the exterior frame plane when the sash is in the closed sash position. wherein the sash comprises side members (8a, 8b), a top member and a bottom member which together encircles a sash opening, and wherein an insulated glass unit is installed in and connected to the sash, wherein the insulated glass unit comprises multiple glass sheets and a sealed inert gas or vacuum in an insulating space between the glass sheets, wherein the insulated glass unit comprises an inwardly facing major surface for facing the interior of the building and an outwardly facing major surface for facing away from interior of the building, wherein an outer weather shield is connected to the sash, wherein the outer weather shield is transparent to at least visible light and comprises an interior major surface and an exterior major surface, wherein the outer weather shield is configured to cover the sash opening and wherein an air gap is provided between the interior major surface of the weather shield and the outwardly facing major surface of the insulated glass unit, wherein the outer weather shield is connected to the sash so as to move together with the sash and the insulated glass unit when the sash is moved between the closed sash position and the open sash position, wherein the weather shield is further movably connected to the sash by means of a further hinge arrangement allowing the weather shield to be moved relative to the sash and the insulated glass unit between a closed weather shield position and an open weather shield position, wherein the exterior of the fixation frame defines an exterior frame plane defined by the outermost surfaces of the fixation frame, and wherein the exterior frame plane extends across and over the frame opening which is encircled by frame members (3a-3c) of the frame, characterized in that at least a part of the insulated glass unit is configured to move from a position above the exterior frame plane and into the frame opening when the sash is moved from the open to the closed sash position, so that the outwardly facing major surface of the insulated glass unit is placed in the frame opening below the exterior frame plane with a distance to the exterior frame plane when the sash is in the closed sash position.