A thermal insulating door or window, especially roof hatch, including a fixed casing and a casement rotatably connected to the frame via hinges around a rotation axis between an open position and a closed position, where parts of the door or window facing an external environment in a use position are thermally separated from parts of the door or window facing an interior space in the use position, and the fixed casing and the casement are thermal insulated, and a thermal insulation is arranged between the fixed casing and the casement, the fixed casing and the casement are equipped with a locking mechanism consisting of cooperating lock parts (13, 14) that secure the casement in its closed position when folded over the fixed casing, characterized in that the the fixed casing comprises a peripheral base frame part and a peripheral linked frame part connected to the base frame part, the casement comprises a cover facing the external environment, a thermal insulating cover insert connected to an inner side of the cover and a casement frame connected to the cover and surrounding the thermal insulating cover insert, the linked frame part connected to the base frame part is formed by a prefabricated plastic door and window fixed casing, and the casement frame connected to the cover and surrounding the thermal insulating cover insert is formed by a prefabricated plastic door and window casement that cooperates with said prefabricated plastic door anc window fixed casing, the thermal insulation arranged between the fixed casing and the casement is formed as at least one elastic insulation arranged between a surface of the casement frame folded over the linked frame part facing the linked frame part and a connecting surface of the linked frame part, running along the entire length of the casement frame, the hinges enabling the casement frame to rotate relative to the fixed casing comprise a first hinge part attached to the fixed casing and a second hinge part attached to the casement frame ensuring separation and connection of the casement from and to the fixed casing in a direction perpendicular to the axis of rotation when opened at an angle of at least 110° relative to the fixed casing. where parts of the door or window facing an external environment in a use position are thermally separated from parts of the door or window facing an interior space in the use position, and the fixed casing and the casement are thermal insulated, and a thermal insulation is arranged between the fixed casing and the casement, the fixed casing and the casement are equipped with a locking mechanism consisting of cooperating lock parts (13, 14) that secure the casement in its closed position when folded over the fixed casing, characterized in that the the fixed casing comprises a peripheral base frame part and a peripheral linked frame part connected to the base frame part, the casement comprises a cover facing the external environment, a thermal insulating cover insert connected to an inner side of the cover and a casement frame connected to the cover and surrounding the thermal insulating cover insert, the linked frame part connected to the base frame part is formed by a prefabricated plastic door and window fixed casing, and the casement frame connected to the cover and surrounding the thermal insulating cover insert is formed by a prefabricated plastic door and window casement that cooperates with said prefabricated plastic door anc window fixed casing, the thermal insulation arranged between the fixed casing and the casement is formed as at least one elastic insulation arranged between a surface of the casement frame folded over the linked frame part facing the linked frame part and a connecting surface of the linked frame part, running along the entire length of the casement frame, the hinges enabling the casement frame to rotate relative to the fixed casing comprise a first hinge part attached to the fixed casing and a second hinge part attached to the casement frame ensuring separation and connection of the casement from and to the fixed casing in a direction perpendicular to the axis of rotation when opened at an angle of at least 110° relative to the fixed casing.